1 files changed, 5604 insertions, 0 deletions

diff --git a/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
new file mode 100644
index 000000000000..67343d11d333
--- /dev/null
+++ b/contrib/llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -0,0 +1,5604 @@
+//===--- SemaTemplateInstantiateDecl.cpp - C++ Template Decl Instantiation ===/
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//===----------------------------------------------------------------------===/
+//
+//  This file implements C++ template instantiation for declarations.
+//
+//===----------------------------------------------------------------------===/
+#include "clang/Sema/SemaInternal.h"
+#include "clang/AST/ASTConsumer.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/ASTMutationListener.h"
+#include "clang/AST/DeclTemplate.h"
+#include "clang/AST/DeclVisitor.h"
+#include "clang/AST/DependentDiagnostic.h"
+#include "clang/AST/Expr.h"
+#include "clang/AST/ExprCXX.h"
+#include "clang/AST/PrettyDeclStackTrace.h"
+#include "clang/AST/TypeLoc.h"
+#include "clang/Sema/Initialization.h"
+#include "clang/Sema/Lookup.h"
+#include "clang/Sema/Template.h"
+#include "clang/Sema/TemplateInstCallback.h"
+#include "llvm/Support/TimeProfiler.h"
+
+using namespace clang;
+
+static bool isDeclWithinFunction(const Decl *D) {
+  const DeclContext *DC = D->getDeclContext();
+  if (DC->isFunctionOrMethod())
+    return true;
+
+  if (DC->isRecord())
+    return cast<CXXRecordDecl>(DC)->isLocalClass();
+
+  return false;
+}
+
+template<typename DeclT>
+static bool SubstQualifier(Sema &SemaRef, const DeclT *OldDecl, DeclT *NewDecl,
+                           const MultiLevelTemplateArgumentList &TemplateArgs) {
+  if (!OldDecl->getQualifierLoc())
+    return false;
+
+  assert((NewDecl->getFriendObjectKind() ||
+          !OldDecl->getLexicalDeclContext()->isDependentContext()) &&
+         "non-friend with qualified name defined in dependent context");
+  Sema::ContextRAII SavedContext(
+      SemaRef,
+      const_cast<DeclContext *>(NewDecl->getFriendObjectKind()
+                                    ? NewDecl->getLexicalDeclContext()
+                                    : OldDecl->getLexicalDeclContext()));
+
+  NestedNameSpecifierLoc NewQualifierLoc
+      = SemaRef.SubstNestedNameSpecifierLoc(OldDecl->getQualifierLoc(),
+                                            TemplateArgs);
+
+  if (!NewQualifierLoc)
+    return true;
+
+  NewDecl->setQualifierInfo(NewQualifierLoc);
+  return false;
+}
+
+bool TemplateDeclInstantiator::SubstQualifier(const DeclaratorDecl *OldDecl,
+                                              DeclaratorDecl *NewDecl) {
+  return ::SubstQualifier(SemaRef, OldDecl, NewDecl, TemplateArgs);
+}
+
+bool TemplateDeclInstantiator::SubstQualifier(const TagDecl *OldDecl,
+                                              TagDecl *NewDecl) {
+  return ::SubstQualifier(SemaRef, OldDecl, NewDecl, TemplateArgs);
+}
+
+// Include attribute instantiation code.
+#include "clang/Sema/AttrTemplateInstantiate.inc"
+
+static void instantiateDependentAlignedAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const AlignedAttr *Aligned, Decl *New, bool IsPackExpansion) {
+  if (Aligned->isAlignmentExpr()) {
+    // The alignment expression is a constant expression.
+    EnterExpressionEvaluationContext Unevaluated(
+        S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+    ExprResult Result = S.SubstExpr(Aligned->getAlignmentExpr(), TemplateArgs);
+    if (!Result.isInvalid())
+      S.AddAlignedAttr(Aligned->getLocation(), New, Result.getAs<Expr>(),
+                       Aligned->getSpellingListIndex(), IsPackExpansion);
+  } else {
+    TypeSourceInfo *Result = S.SubstType(Aligned->getAlignmentType(),
+                                         TemplateArgs, Aligned->getLocation(),
+                                         DeclarationName());
+    if (Result)
+      S.AddAlignedAttr(Aligned->getLocation(), New, Result,
+                       Aligned->getSpellingListIndex(), IsPackExpansion);
+  }
+}
+
+static void instantiateDependentAlignedAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const AlignedAttr *Aligned, Decl *New) {
+  if (!Aligned->isPackExpansion()) {
+    instantiateDependentAlignedAttr(S, TemplateArgs, Aligned, New, false);
+    return;
+  }
+
+  SmallVector<UnexpandedParameterPack, 2> Unexpanded;
+  if (Aligned->isAlignmentExpr())
+    S.collectUnexpandedParameterPacks(Aligned->getAlignmentExpr(),
+                                      Unexpanded);
+  else
+    S.collectUnexpandedParameterPacks(Aligned->getAlignmentType()->getTypeLoc(),
+                                      Unexpanded);
+  assert(!Unexpanded.empty() && "Pack expansion without parameter packs?");
+
+  // Determine whether we can expand this attribute pack yet.
+  bool Expand = true, RetainExpansion = false;
+  Optional<unsigned> NumExpansions;
+  // FIXME: Use the actual location of the ellipsis.
+  SourceLocation EllipsisLoc = Aligned->getLocation();
+  if (S.CheckParameterPacksForExpansion(EllipsisLoc, Aligned->getRange(),
+                                        Unexpanded, TemplateArgs, Expand,
+                                        RetainExpansion, NumExpansions))
+    return;
+
+  if (!Expand) {
+    Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(S, -1);
+    instantiateDependentAlignedAttr(S, TemplateArgs, Aligned, New, true);
+  } else {
+    for (unsigned I = 0; I != *NumExpansions; ++I) {
+      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(S, I);
+      instantiateDependentAlignedAttr(S, TemplateArgs, Aligned, New, false);
+    }
+  }
+}
+
+static void instantiateDependentAssumeAlignedAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const AssumeAlignedAttr *Aligned, Decl *New) {
+  // The alignment expression is a constant expression.
+  EnterExpressionEvaluationContext Unevaluated(
+      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+
+  Expr *E, *OE = nullptr;
+  ExprResult Result = S.SubstExpr(Aligned->getAlignment(), TemplateArgs);
+  if (Result.isInvalid())
+    return;
+  E = Result.getAs<Expr>();
+
+  if (Aligned->getOffset()) {
+    Result = S.SubstExpr(Aligned->getOffset(), TemplateArgs);
+    if (Result.isInvalid())
+      return;
+    OE = Result.getAs<Expr>();
+  }
+
+  S.AddAssumeAlignedAttr(Aligned->getLocation(), New, E, OE,
+                         Aligned->getSpellingListIndex());
+}
+
+static void instantiateDependentAlignValueAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const AlignValueAttr *Aligned, Decl *New) {
+  // The alignment expression is a constant expression.
+  EnterExpressionEvaluationContext Unevaluated(
+      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+  ExprResult Result = S.SubstExpr(Aligned->getAlignment(), TemplateArgs);
+  if (!Result.isInvalid())
+    S.AddAlignValueAttr(Aligned->getLocation(), New, Result.getAs<Expr>(),
+                        Aligned->getSpellingListIndex());
+}
+
+static void instantiateDependentAllocAlignAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const AllocAlignAttr *Align, Decl *New) {
+  Expr *Param = IntegerLiteral::Create(
+      S.getASTContext(),
+      llvm::APInt(64, Align->getParamIndex().getSourceIndex()),
+      S.getASTContext().UnsignedLongLongTy, Align->getLocation());
+  S.AddAllocAlignAttr(Align->getLocation(), New, Param,
+                      Align->getSpellingListIndex());
+}
+
+static Expr *instantiateDependentFunctionAttrCondition(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const Attr *A, Expr *OldCond, const Decl *Tmpl, FunctionDecl *New) {
+  Expr *Cond = nullptr;
+  {
+    Sema::ContextRAII SwitchContext(S, New);
+    EnterExpressionEvaluationContext Unevaluated(
+        S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+    ExprResult Result = S.SubstExpr(OldCond, TemplateArgs);
+    if (Result.isInvalid())
+      return nullptr;
+    Cond = Result.getAs<Expr>();
+  }
+  if (!Cond->isTypeDependent()) {
+    ExprResult Converted = S.PerformContextuallyConvertToBool(Cond);
+    if (Converted.isInvalid())
+      return nullptr;
+    Cond = Converted.get();
+  }
+
+  SmallVector<PartialDiagnosticAt, 8> Diags;
+  if (OldCond->isValueDependent() && !Cond->isValueDependent() &&
+      !Expr::isPotentialConstantExprUnevaluated(Cond, New, Diags)) {
+    S.Diag(A->getLocation(), diag::err_attr_cond_never_constant_expr) << A;
+    for (const auto &P : Diags)
+      S.Diag(P.first, P.second);
+    return nullptr;
+  }
+  return Cond;
+}
+
+static void instantiateDependentEnableIfAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const EnableIfAttr *EIA, const Decl *Tmpl, FunctionDecl *New) {
+  Expr *Cond = instantiateDependentFunctionAttrCondition(
+      S, TemplateArgs, EIA, EIA->getCond(), Tmpl, New);
+
+  if (Cond)
+    New->addAttr(new (S.getASTContext()) EnableIfAttr(
+        EIA->getLocation(), S.getASTContext(), Cond, EIA->getMessage(),
+        EIA->getSpellingListIndex()));
+}
+
+static void instantiateDependentDiagnoseIfAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const DiagnoseIfAttr *DIA, const Decl *Tmpl, FunctionDecl *New) {
+  Expr *Cond = instantiateDependentFunctionAttrCondition(
+      S, TemplateArgs, DIA, DIA->getCond(), Tmpl, New);
+
+  if (Cond)
+    New->addAttr(new (S.getASTContext()) DiagnoseIfAttr(
+        DIA->getLocation(), S.getASTContext(), Cond, DIA->getMessage(),
+        DIA->getDiagnosticType(), DIA->getArgDependent(), New,
+        DIA->getSpellingListIndex()));
+}
+
+// Constructs and adds to New a new instance of CUDALaunchBoundsAttr using
+// template A as the base and arguments from TemplateArgs.
+static void instantiateDependentCUDALaunchBoundsAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const CUDALaunchBoundsAttr &Attr, Decl *New) {
+  // The alignment expression is a constant expression.
+  EnterExpressionEvaluationContext Unevaluated(
+      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+
+  ExprResult Result = S.SubstExpr(Attr.getMaxThreads(), TemplateArgs);
+  if (Result.isInvalid())
+    return;
+  Expr *MaxThreads = Result.getAs<Expr>();
+
+  Expr *MinBlocks = nullptr;
+  if (Attr.getMinBlocks()) {
+    Result = S.SubstExpr(Attr.getMinBlocks(), TemplateArgs);
+    if (Result.isInvalid())
+      return;
+    MinBlocks = Result.getAs<Expr>();
+  }
+
+  S.AddLaunchBoundsAttr(Attr.getLocation(), New, MaxThreads, MinBlocks,
+                        Attr.getSpellingListIndex());
+}
+
+static void
+instantiateDependentModeAttr(Sema &S,
+                             const MultiLevelTemplateArgumentList &TemplateArgs,
+                             const ModeAttr &Attr, Decl *New) {
+  S.AddModeAttr(Attr.getRange(), New, Attr.getMode(),
+                Attr.getSpellingListIndex(), /*InInstantiation=*/true);
+}
+
+/// Instantiation of 'declare simd' attribute and its arguments.
+static void instantiateOMPDeclareSimdDeclAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const OMPDeclareSimdDeclAttr &Attr, Decl *New) {
+  // Allow 'this' in clauses with varlists.
+  if (auto *FTD = dyn_cast<FunctionTemplateDecl>(New))
+    New = FTD->getTemplatedDecl();
+  auto *FD = cast<FunctionDecl>(New);
+  auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(FD->getDeclContext());
+  SmallVector<Expr *, 4> Uniforms, Aligneds, Alignments, Linears, Steps;
+  SmallVector<unsigned, 4> LinModifiers;
+
+  auto SubstExpr = [&](Expr *E) -> ExprResult {
+    if (auto *DRE = dyn_cast<DeclRefExpr>(E->IgnoreParenImpCasts()))
+      if (auto *PVD = dyn_cast<ParmVarDecl>(DRE->getDecl())) {
+        Sema::ContextRAII SavedContext(S, FD);
+        LocalInstantiationScope Local(S);
+        if (FD->getNumParams() > PVD->getFunctionScopeIndex())
+          Local.InstantiatedLocal(
+              PVD, FD->getParamDecl(PVD->getFunctionScopeIndex()));
+        return S.SubstExpr(E, TemplateArgs);
+      }
+    Sema::CXXThisScopeRAII ThisScope(S, ThisContext, Qualifiers(),
+                                     FD->isCXXInstanceMember());
+    return S.SubstExpr(E, TemplateArgs);
+  };
+
+  // Substitute a single OpenMP clause, which is a potentially-evaluated
+  // full-expression.
+  auto Subst = [&](Expr *E) -> ExprResult {
+    EnterExpressionEvaluationContext Evaluated(
+        S, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
+    ExprResult Res = SubstExpr(E);
+    if (Res.isInvalid())
+      return Res;
+    return S.ActOnFinishFullExpr(Res.get(), false);
+  };
+
+  ExprResult Simdlen;
+  if (auto *E = Attr.getSimdlen())
+    Simdlen = Subst(E);
+
+  if (Attr.uniforms_size() > 0) {
+    for(auto *E : Attr.uniforms()) {
+      ExprResult Inst = Subst(E);
+      if (Inst.isInvalid())
+        continue;
+      Uniforms.push_back(Inst.get());
+    }
+  }
+
+  auto AI = Attr.alignments_begin();
+  for (auto *E : Attr.aligneds()) {
+    ExprResult Inst = Subst(E);
+    if (Inst.isInvalid())
+      continue;
+    Aligneds.push_back(Inst.get());
+    Inst = ExprEmpty();
+    if (*AI)
+      Inst = S.SubstExpr(*AI, TemplateArgs);
+    Alignments.push_back(Inst.get());
+    ++AI;
+  }
+
+  auto SI = Attr.steps_begin();
+  for (auto *E : Attr.linears()) {
+    ExprResult Inst = Subst(E);
+    if (Inst.isInvalid())
+      continue;
+    Linears.push_back(Inst.get());
+    Inst = ExprEmpty();
+    if (*SI)
+      Inst = S.SubstExpr(*SI, TemplateArgs);
+    Steps.push_back(Inst.get());
+    ++SI;
+  }
+  LinModifiers.append(Attr.modifiers_begin(), Attr.modifiers_end());
+  (void)S.ActOnOpenMPDeclareSimdDirective(
+      S.ConvertDeclToDeclGroup(New), Attr.getBranchState(), Simdlen.get(),
+      Uniforms, Aligneds, Alignments, Linears, LinModifiers, Steps,
+      Attr.getRange());
+}
+
+static void instantiateDependentAMDGPUFlatWorkGroupSizeAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const AMDGPUFlatWorkGroupSizeAttr &Attr, Decl *New) {
+  // Both min and max expression are constant expressions.
+  EnterExpressionEvaluationContext Unevaluated(
+      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+
+  ExprResult Result = S.SubstExpr(Attr.getMin(), TemplateArgs);
+  if (Result.isInvalid())
+    return;
+  Expr *MinExpr = Result.getAs<Expr>();
+
+  Result = S.SubstExpr(Attr.getMax(), TemplateArgs);
+  if (Result.isInvalid())
+    return;
+  Expr *MaxExpr = Result.getAs<Expr>();
+
+  S.addAMDGPUFlatWorkGroupSizeAttr(Attr.getLocation(), New, MinExpr, MaxExpr,
+                                   Attr.getSpellingListIndex());
+}
+
+static ExplicitSpecifier
+instantiateExplicitSpecifier(Sema &S,
+                             const MultiLevelTemplateArgumentList &TemplateArgs,
+                             ExplicitSpecifier ES, FunctionDecl *New) {
+  if (!ES.getExpr())
+    return ES;
+  Expr *OldCond = ES.getExpr();
+  Expr *Cond = nullptr;
+  {
+    EnterExpressionEvaluationContext Unevaluated(
+        S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+    ExprResult SubstResult = S.SubstExpr(OldCond, TemplateArgs);
+    if (SubstResult.isInvalid()) {
+      return ExplicitSpecifier::Invalid();
+    }
+    Cond = SubstResult.get();
+  }
+  ExplicitSpecifier Result(Cond, ES.getKind());
+  if (!Cond->isTypeDependent())
+    S.tryResolveExplicitSpecifier(Result);
+  return Result;
+}
+
+static void instantiateDependentAMDGPUWavesPerEUAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const AMDGPUWavesPerEUAttr &Attr, Decl *New) {
+  // Both min and max expression are constant expressions.
+  EnterExpressionEvaluationContext Unevaluated(
+      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+
+  ExprResult Result = S.SubstExpr(Attr.getMin(), TemplateArgs);
+  if (Result.isInvalid())
+    return;
+  Expr *MinExpr = Result.getAs<Expr>();
+
+  Expr *MaxExpr = nullptr;
+  if (auto Max = Attr.getMax()) {
+    Result = S.SubstExpr(Max, TemplateArgs);
+    if (Result.isInvalid())
+      return;
+    MaxExpr = Result.getAs<Expr>();
+  }
+
+  S.addAMDGPUWavesPerEUAttr(Attr.getLocation(), New, MinExpr, MaxExpr,
+                            Attr.getSpellingListIndex());
+}
+
+void Sema::InstantiateAttrsForDecl(
+    const MultiLevelTemplateArgumentList &TemplateArgs, const Decl *Tmpl,
+    Decl *New, LateInstantiatedAttrVec *LateAttrs,
+    LocalInstantiationScope *OuterMostScope) {
+  if (NamedDecl *ND = dyn_cast<NamedDecl>(New)) {
+    for (const auto *TmplAttr : Tmpl->attrs()) {
+      // FIXME: If any of the special case versions from InstantiateAttrs become
+      // applicable to template declaration, we'll need to add them here.
+      CXXThisScopeRAII ThisScope(
+          *this, dyn_cast_or_null<CXXRecordDecl>(ND->getDeclContext()),
+          Qualifiers(), ND->isCXXInstanceMember());
+
+      Attr *NewAttr = sema::instantiateTemplateAttributeForDecl(
+          TmplAttr, Context, *this, TemplateArgs);
+      if (NewAttr)
+        New->addAttr(NewAttr);
+    }
+  }
+}
+
+static Sema::RetainOwnershipKind
+attrToRetainOwnershipKind(const Attr *A) {
+  switch (A->getKind()) {
+  case clang::attr::CFConsumed:
+    return Sema::RetainOwnershipKind::CF;
+  case clang::attr::OSConsumed:
+    return Sema::RetainOwnershipKind::OS;
+  case clang::attr::NSConsumed:
+    return Sema::RetainOwnershipKind::NS;
+  default:
+    llvm_unreachable("Wrong argument supplied");
+  }
+}
+
+void Sema::InstantiateAttrs(const MultiLevelTemplateArgumentList &TemplateArgs,
+                            const Decl *Tmpl, Decl *New,
+                            LateInstantiatedAttrVec *LateAttrs,
+                            LocalInstantiationScope *OuterMostScope) {
+  for (const auto *TmplAttr : Tmpl->attrs()) {
+    // FIXME: This should be generalized to more than just the AlignedAttr.
+    const AlignedAttr *Aligned = dyn_cast<AlignedAttr>(TmplAttr);
+    if (Aligned && Aligned->isAlignmentDependent()) {
+      instantiateDependentAlignedAttr(*this, TemplateArgs, Aligned, New);
+      continue;
+    }
+
+    const AssumeAlignedAttr *AssumeAligned = dyn_cast<AssumeAlignedAttr>(TmplAttr);
+    if (AssumeAligned) {
+      instantiateDependentAssumeAlignedAttr(*this, TemplateArgs, AssumeAligned, New);
+      continue;
+    }
+
+    const AlignValueAttr *AlignValue = dyn_cast<AlignValueAttr>(TmplAttr);
+    if (AlignValue) {
+      instantiateDependentAlignValueAttr(*this, TemplateArgs, AlignValue, New);
+      continue;
+    }
+
+    if (const auto *AllocAlign = dyn_cast<AllocAlignAttr>(TmplAttr)) {
+      instantiateDependentAllocAlignAttr(*this, TemplateArgs, AllocAlign, New);
+      continue;
+    }
+
+
+    if (const auto *EnableIf = dyn_cast<EnableIfAttr>(TmplAttr)) {
+      instantiateDependentEnableIfAttr(*this, TemplateArgs, EnableIf, Tmpl,
+                                       cast<FunctionDecl>(New));
+      continue;
+    }
+
+    if (const auto *DiagnoseIf = dyn_cast<DiagnoseIfAttr>(TmplAttr)) {
+      instantiateDependentDiagnoseIfAttr(*this, TemplateArgs, DiagnoseIf, Tmpl,
+                                         cast<FunctionDecl>(New));
+      continue;
+    }
+
+    if (const CUDALaunchBoundsAttr *CUDALaunchBounds =
+            dyn_cast<CUDALaunchBoundsAttr>(TmplAttr)) {
+      instantiateDependentCUDALaunchBoundsAttr(*this, TemplateArgs,
+                                               *CUDALaunchBounds, New);
+      continue;
+    }
+
+    if (const ModeAttr *Mode = dyn_cast<ModeAttr>(TmplAttr)) {
+      instantiateDependentModeAttr(*this, TemplateArgs, *Mode, New);
+      continue;
+    }
+
+    if (const auto *OMPAttr = dyn_cast<OMPDeclareSimdDeclAttr>(TmplAttr)) {
+      instantiateOMPDeclareSimdDeclAttr(*this, TemplateArgs, *OMPAttr, New);
+      continue;
+    }
+
+    if (const AMDGPUFlatWorkGroupSizeAttr *AMDGPUFlatWorkGroupSize =
+            dyn_cast<AMDGPUFlatWorkGroupSizeAttr>(TmplAttr)) {
+      instantiateDependentAMDGPUFlatWorkGroupSizeAttr(
+          *this, TemplateArgs, *AMDGPUFlatWorkGroupSize, New);
+    }
+
+    if (const AMDGPUWavesPerEUAttr *AMDGPUFlatWorkGroupSize =
+            dyn_cast<AMDGPUWavesPerEUAttr>(TmplAttr)) {
+      instantiateDependentAMDGPUWavesPerEUAttr(*this, TemplateArgs,
+                                               *AMDGPUFlatWorkGroupSize, New);
+    }
+
+    // Existing DLL attribute on the instantiation takes precedence.
+    if (TmplAttr->getKind() == attr::DLLExport ||
+        TmplAttr->getKind() == attr::DLLImport) {
+      if (New->hasAttr<DLLExportAttr>() || New->hasAttr<DLLImportAttr>()) {
+        continue;
+      }
+    }
+
+    if (auto ABIAttr = dyn_cast<ParameterABIAttr>(TmplAttr)) {
+      AddParameterABIAttr(ABIAttr->getRange(), New, ABIAttr->getABI(),
+                          ABIAttr->getSpellingListIndex());
+      continue;
+    }
+
+    if (isa<NSConsumedAttr>(TmplAttr) || isa<OSConsumedAttr>(TmplAttr) ||
+        isa<CFConsumedAttr>(TmplAttr)) {
+      AddXConsumedAttr(New, TmplAttr->getRange(),
+                       TmplAttr->getSpellingListIndex(),
+                       attrToRetainOwnershipKind(TmplAttr),
+                       /*template instantiation=*/true);
+      continue;
+    }
+
+    assert(!TmplAttr->isPackExpansion());
+    if (TmplAttr->isLateParsed() && LateAttrs) {
+      // Late parsed attributes must be instantiated and attached after the
+      // enclosing class has been instantiated.  See Sema::InstantiateClass.
+      LocalInstantiationScope *Saved = nullptr;
+      if (CurrentInstantiationScope)
+        Saved = CurrentInstantiationScope->cloneScopes(OuterMostScope);
+      LateAttrs->push_back(LateInstantiatedAttribute(TmplAttr, Saved, New));
+    } else {
+      // Allow 'this' within late-parsed attributes.
+      NamedDecl *ND = dyn_cast<NamedDecl>(New);
+      CXXRecordDecl *ThisContext =
+          dyn_cast_or_null<CXXRecordDecl>(ND->getDeclContext());
+      CXXThisScopeRAII ThisScope(*this, ThisContext, Qualifiers(),
+                                 ND && ND->isCXXInstanceMember());
+
+      Attr *NewAttr = sema::instantiateTemplateAttribute(TmplAttr, Context,
+                                                         *this, TemplateArgs);
+      if (NewAttr)
+        New->addAttr(NewAttr);
+    }
+  }
+}
+
+/// Get the previous declaration of a declaration for the purposes of template
+/// instantiation. If this finds a previous declaration, then the previous
+/// declaration of the instantiation of D should be an instantiation of the
+/// result of this function.
+template<typename DeclT>
+static DeclT *getPreviousDeclForInstantiation(DeclT *D) {
+  DeclT *Result = D->getPreviousDecl();
+
+  // If the declaration is within a class, and the previous declaration was
+  // merged from a different definition of that class, then we don't have a
+  // previous declaration for the purpose of template instantiation.
+  if (Result && isa<CXXRecordDecl>(D->getDeclContext()) &&
+      D->getLexicalDeclContext() != Result->getLexicalDeclContext())
+    return nullptr;
+
+  return Result;
+}
+
+Decl *
+TemplateDeclInstantiator::VisitTranslationUnitDecl(TranslationUnitDecl *D) {
+  llvm_unreachable("Translation units cannot be instantiated");
+}
+
+Decl *
+TemplateDeclInstantiator::VisitPragmaCommentDecl(PragmaCommentDecl *D) {
+  llvm_unreachable("pragma comment cannot be instantiated");
+}
+
+Decl *TemplateDeclInstantiator::VisitPragmaDetectMismatchDecl(
+    PragmaDetectMismatchDecl *D) {
+  llvm_unreachable("pragma comment cannot be instantiated");
+}
+
+Decl *
+TemplateDeclInstantiator::VisitExternCContextDecl(ExternCContextDecl *D) {
+  llvm_unreachable("extern \"C\" context cannot be instantiated");
+}
+
+Decl *
+TemplateDeclInstantiator::VisitLabelDecl(LabelDecl *D) {
+  LabelDecl *Inst = LabelDecl::Create(SemaRef.Context, Owner, D->getLocation(),
+                                      D->getIdentifier());
+  Owner->addDecl(Inst);
+  return Inst;
+}
+
+Decl *
+TemplateDeclInstantiator::VisitNamespaceDecl(NamespaceDecl *D) {
+  llvm_unreachable("Namespaces cannot be instantiated");
+}
+
+Decl *
+TemplateDeclInstantiator::VisitNamespaceAliasDecl(NamespaceAliasDecl *D) {
+  NamespaceAliasDecl *Inst
+    = NamespaceAliasDecl::Create(SemaRef.Context, Owner,
+                                 D->getNamespaceLoc(),
+                                 D->getAliasLoc(),
+                                 D->getIdentifier(),
+                                 D->getQualifierLoc(),
+                                 D->getTargetNameLoc(),
+                                 D->getNamespace());
+  Owner->addDecl(Inst);
+  return Inst;
+}
+
+Decl *TemplateDeclInstantiator::InstantiateTypedefNameDecl(TypedefNameDecl *D,
+                                                           bool IsTypeAlias) {
+  bool Invalid = false;
+  TypeSourceInfo *DI = D->getTypeSourceInfo();
+  if (DI->getType()->isInstantiationDependentType() ||
+      DI->getType()->isVariablyModifiedType()) {
+    DI = SemaRef.SubstType(DI, TemplateArgs,
+                           D->getLocation(), D->getDeclName());
+    if (!DI) {
+      Invalid = true;
+      DI = SemaRef.Context.getTrivialTypeSourceInfo(SemaRef.Context.IntTy);
+    }
+  } else {
+    SemaRef.MarkDeclarationsReferencedInType(D->getLocation(), DI->getType());
+  }
+
+  // HACK: g++ has a bug where it gets the value kind of ?: wrong.
+  // libstdc++ relies upon this bug in its implementation of common_type.
+  // If we happen to be processing that implementation, fake up the g++ ?:
+  // semantics. See LWG issue 2141 for more information on the bug.
+  const DecltypeType *DT = DI->getType()->getAs<DecltypeType>();
+  CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D->getDeclContext());
+  if (DT && RD && isa<ConditionalOperator>(DT->getUnderlyingExpr()) &&
+      DT->isReferenceType() &&
+      RD->getEnclosingNamespaceContext() == SemaRef.getStdNamespace() &&
+      RD->getIdentifier() && RD->getIdentifier()->isStr("common_type") &&
+      D->getIdentifier() && D->getIdentifier()->isStr("type") &&
+      SemaRef.getSourceManager().isInSystemHeader(D->getBeginLoc()))
+    // Fold it to the (non-reference) type which g++ would have produced.
+    DI = SemaRef.Context.getTrivialTypeSourceInfo(
+      DI->getType().getNonReferenceType());
+
+  // Create the new typedef
+  TypedefNameDecl *Typedef;
+  if (IsTypeAlias)
+    Typedef = TypeAliasDecl::Create(SemaRef.Context, Owner, D->getBeginLoc(),
+                                    D->getLocation(), D->getIdentifier(), DI);
+  else
+    Typedef = TypedefDecl::Create(SemaRef.Context, Owner, D->getBeginLoc(),
+                                  D->getLocation(), D->getIdentifier(), DI);
+  if (Invalid)
+    Typedef->setInvalidDecl();
+
+  // If the old typedef was the name for linkage purposes of an anonymous
+  // tag decl, re-establish that relationship for the new typedef.
+  if (const TagType *oldTagType = D->getUnderlyingType()->getAs<TagType>()) {
+    TagDecl *oldTag = oldTagType->getDecl();
+    if (oldTag->getTypedefNameForAnonDecl() == D && !Invalid) {
+      TagDecl *newTag = DI->getType()->castAs<TagType>()->getDecl();
+      assert(!newTag->hasNameForLinkage());
+      newTag->setTypedefNameForAnonDecl(Typedef);
+    }
+  }
+
+  if (TypedefNameDecl *Prev = getPreviousDeclForInstantiation(D)) {
+    NamedDecl *InstPrev = SemaRef.FindInstantiatedDecl(D->getLocation(), Prev,
+                                                       TemplateArgs);
+    if (!InstPrev)
+      return nullptr;
+
+    TypedefNameDecl *InstPrevTypedef = cast<TypedefNameDecl>(InstPrev);
+
+    // If the typedef types are not identical, reject them.
+    SemaRef.isIncompatibleTypedef(InstPrevTypedef, Typedef);
+
+    Typedef->setPreviousDecl(InstPrevTypedef);
+  }
+
+  SemaRef.InstantiateAttrs(TemplateArgs, D, Typedef);
+
+  Typedef->setAccess(D->getAccess());
+
+  return Typedef;
+}
+
+Decl *TemplateDeclInstantiator::VisitTypedefDecl(TypedefDecl *D) {
+  Decl *Typedef = InstantiateTypedefNameDecl(D, /*IsTypeAlias=*/false);
+  if (Typedef)
+    Owner->addDecl(Typedef);
+  return Typedef;
+}
+
+Decl *TemplateDeclInstantiator::VisitTypeAliasDecl(TypeAliasDecl *D) {
+  Decl *Typedef = InstantiateTypedefNameDecl(D, /*IsTypeAlias=*/true);
+  if (Typedef)
+    Owner->addDecl(Typedef);
+  return Typedef;
+}
+
+Decl *
+TemplateDeclInstantiator::VisitTypeAliasTemplateDecl(TypeAliasTemplateDecl *D) {
+  // Create a local instantiation scope for this type alias template, which
+  // will contain the instantiations of the template parameters.
+  LocalInstantiationScope Scope(SemaRef);
+
+  TemplateParameterList *TempParams = D->getTemplateParameters();
+  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
+  if (!InstParams)
+    return nullptr;
+
+  TypeAliasDecl *Pattern = D->getTemplatedDecl();
+
+  TypeAliasTemplateDecl *PrevAliasTemplate = nullptr;
+  if (getPreviousDeclForInstantiation<TypedefNameDecl>(Pattern)) {
+    DeclContext::lookup_result Found = Owner->lookup(Pattern->getDeclName());
+    if (!Found.empty()) {
+      PrevAliasTemplate = dyn_cast<TypeAliasTemplateDecl>(Found.front());
+    }
+  }
+
+  TypeAliasDecl *AliasInst = cast_or_null<TypeAliasDecl>(
+    InstantiateTypedefNameDecl(Pattern, /*IsTypeAlias=*/true));
+  if (!AliasInst)
+    return nullptr;
+
+  TypeAliasTemplateDecl *Inst
+    = TypeAliasTemplateDecl::Create(SemaRef.Context, Owner, D->getLocation(),
+                                    D->getDeclName(), InstParams, AliasInst);
+  AliasInst->setDescribedAliasTemplate(Inst);
+  if (PrevAliasTemplate)
+    Inst->setPreviousDecl(PrevAliasTemplate);
+
+  Inst->setAccess(D->getAccess());
+
+  if (!PrevAliasTemplate)
+    Inst->setInstantiatedFromMemberTemplate(D);
+
+  Owner->addDecl(Inst);
+
+  return Inst;
+}
+
+Decl *TemplateDeclInstantiator::VisitBindingDecl(BindingDecl *D) {
+  auto *NewBD = BindingDecl::Create(SemaRef.Context, Owner, D->getLocation(),
+                                    D->getIdentifier());
+  NewBD->setReferenced(D->isReferenced());
+  SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewBD);
+  return NewBD;
+}
+
+Decl *TemplateDeclInstantiator::VisitDecompositionDecl(DecompositionDecl *D) {
+  // Transform the bindings first.
+  SmallVector<BindingDecl*, 16> NewBindings;
+  for (auto *OldBD : D->bindings())
+    NewBindings.push_back(cast<BindingDecl>(VisitBindingDecl(OldBD)));
+  ArrayRef<BindingDecl*> NewBindingArray = NewBindings;
+
+  auto *NewDD = cast_or_null<DecompositionDecl>(
+      VisitVarDecl(D, /*InstantiatingVarTemplate=*/false, &NewBindingArray));
+
+  if (!NewDD || NewDD->isInvalidDecl())
+    for (auto *NewBD : NewBindings)
+      NewBD->setInvalidDecl();
+
+  return NewDD;
+}
+
+Decl *TemplateDeclInstantiator::VisitVarDecl(VarDecl *D) {
+  return VisitVarDecl(D, /*InstantiatingVarTemplate=*/false);
+}
+
+Decl *TemplateDeclInstantiator::VisitVarDecl(VarDecl *D,
+                                             bool InstantiatingVarTemplate,
+                                             ArrayRef<BindingDecl*> *Bindings) {
+
+  // Do substitution on the type of the declaration
+  TypeSourceInfo *DI = SemaRef.SubstType(
+      D->getTypeSourceInfo(), TemplateArgs, D->getTypeSpecStartLoc(),
+      D->getDeclName(), /*AllowDeducedTST*/true);
+  if (!DI)
+    return nullptr;
+
+  if (DI->getType()->isFunctionType()) {
+    SemaRef.Diag(D->getLocation(), diag::err_variable_instantiates_to_function)
+      << D->isStaticDataMember() << DI->getType();
+    return nullptr;
+  }
+
+  DeclContext *DC = Owner;
+  if (D->isLocalExternDecl())
+    SemaRef.adjustContextForLocalExternDecl(DC);
+
+  // Build the instantiated declaration.
+  VarDecl *Var;
+  if (Bindings)
+    Var = DecompositionDecl::Create(SemaRef.Context, DC, D->getInnerLocStart(),
+                                    D->getLocation(), DI->getType(), DI,
+                                    D->getStorageClass(), *Bindings);
+  else
+    Var = VarDecl::Create(SemaRef.Context, DC, D->getInnerLocStart(),
+                          D->getLocation(), D->getIdentifier(), DI->getType(),
+                          DI, D->getStorageClass());
+
+  // In ARC, infer 'retaining' for variables of retainable type.
+  if (SemaRef.getLangOpts().ObjCAutoRefCount &&
+      SemaRef.inferObjCARCLifetime(Var))
+    Var->setInvalidDecl();
+
+  // Substitute the nested name specifier, if any.
+  if (SubstQualifier(D, Var))
+    return nullptr;
+
+  SemaRef.BuildVariableInstantiation(Var, D, TemplateArgs, LateAttrs, Owner,
+                                     StartingScope, InstantiatingVarTemplate);
+
+  if (D->isNRVOVariable()) {
+    QualType ReturnType = cast<FunctionDecl>(DC)->getReturnType();
+    if (SemaRef.isCopyElisionCandidate(ReturnType, Var, Sema::CES_Strict))
+      Var->setNRVOVariable(true);
+  }
+
+  Var->setImplicit(D->isImplicit());
+
+  if (Var->isStaticLocal())
+    SemaRef.CheckStaticLocalForDllExport(Var);
+
+  return Var;
+}
+
+Decl *TemplateDeclInstantiator::VisitAccessSpecDecl(AccessSpecDecl *D) {
+  AccessSpecDecl* AD
+    = AccessSpecDecl::Create(SemaRef.Context, D->getAccess(), Owner,
+                             D->getAccessSpecifierLoc(), D->getColonLoc());
+  Owner->addHiddenDecl(AD);
+  return AD;
+}
+
+Decl *TemplateDeclInstantiator::VisitFieldDecl(FieldDecl *D) {
+  bool Invalid = false;
+  TypeSourceInfo *DI = D->getTypeSourceInfo();
+  if (DI->getType()->isInstantiationDependentType() ||
+      DI->getType()->isVariablyModifiedType())  {
+    DI = SemaRef.SubstType(DI, TemplateArgs,
+                           D->getLocation(), D->getDeclName());
+    if (!DI) {
+      DI = D->getTypeSourceInfo();
+      Invalid = true;
+    } else if (DI->getType()->isFunctionType()) {
+      // C++ [temp.arg.type]p3:
+      //   If a declaration acquires a function type through a type
+      //   dependent on a template-parameter and this causes a
+      //   declaration that does not use the syntactic form of a
+      //   function declarator to have function type, the program is
+      //   ill-formed.
+      SemaRef.Diag(D->getLocation(), diag::err_field_instantiates_to_function)
+        << DI->getType();
+      Invalid = true;
+    }
+  } else {
+    SemaRef.MarkDeclarationsReferencedInType(D->getLocation(), DI->getType());
+  }
+
+  Expr *BitWidth = D->getBitWidth();
+  if (Invalid)
+    BitWidth = nullptr;
+  else if (BitWidth) {
+    // The bit-width expression is a constant expression.
+    EnterExpressionEvaluationContext Unevaluated(
+        SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+
+    ExprResult InstantiatedBitWidth
+      = SemaRef.SubstExpr(BitWidth, TemplateArgs);
+    if (InstantiatedBitWidth.isInvalid()) {
+      Invalid = true;
+      BitWidth = nullptr;
+    } else
+      BitWidth = InstantiatedBitWidth.getAs<Expr>();
+  }
+
+  FieldDecl *Field = SemaRef.CheckFieldDecl(D->getDeclName(),
+                                            DI->getType(), DI,
+                                            cast<RecordDecl>(Owner),
+                                            D->getLocation(),
+                                            D->isMutable(),
+                                            BitWidth,
+                                            D->getInClassInitStyle(),
+                                            D->getInnerLocStart(),
+                                            D->getAccess(),
+                                            nullptr);
+  if (!Field) {
+    cast<Decl>(Owner)->setInvalidDecl();
+    return nullptr;
+  }
+
+  SemaRef.InstantiateAttrs(TemplateArgs, D, Field, LateAttrs, StartingScope);
+
+  if (Field->hasAttrs())
+    SemaRef.CheckAlignasUnderalignment(Field);
+
+  if (Invalid)
+    Field->setInvalidDecl();
+
+  if (!Field->getDeclName()) {
+    // Keep track of where this decl came from.
+    SemaRef.Context.setInstantiatedFromUnnamedFieldDecl(Field, D);
+  }
+  if (CXXRecordDecl *Parent= dyn_cast<CXXRecordDecl>(Field->getDeclContext())) {
+    if (Parent->isAnonymousStructOrUnion() &&
+        Parent->getRedeclContext()->isFunctionOrMethod())
+      SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Field);
+  }
+
+  Field->setImplicit(D->isImplicit());
+  Field->setAccess(D->getAccess());
+  Owner->addDecl(Field);
+
+  return Field;
+}
+
+Decl *TemplateDeclInstantiator::VisitMSPropertyDecl(MSPropertyDecl *D) {
+  bool Invalid = false;
+  TypeSourceInfo *DI = D->getTypeSourceInfo();
+
+  if (DI->getType()->isVariablyModifiedType()) {
+    SemaRef.Diag(D->getLocation(), diag::err_property_is_variably_modified)
+      << D;
+    Invalid = true;
+  } else if (DI->getType()->isInstantiationDependentType())  {
+    DI = SemaRef.SubstType(DI, TemplateArgs,
+                           D->getLocation(), D->getDeclName());
+    if (!DI) {
+      DI = D->getTypeSourceInfo();
+      Invalid = true;
+    } else if (DI->getType()->isFunctionType()) {
+      // C++ [temp.arg.type]p3:
+      //   If a declaration acquires a function type through a type
+      //   dependent on a template-parameter and this causes a
+      //   declaration that does not use the syntactic form of a
+      //   function declarator to have function type, the program is
+      //   ill-formed.
+      SemaRef.Diag(D->getLocation(), diag::err_field_instantiates_to_function)
+      << DI->getType();
+      Invalid = true;
+    }
+  } else {
+    SemaRef.MarkDeclarationsReferencedInType(D->getLocation(), DI->getType());
+  }
+
+  MSPropertyDecl *Property = MSPropertyDecl::Create(
+      SemaRef.Context, Owner, D->getLocation(), D->getDeclName(), DI->getType(),
+      DI, D->getBeginLoc(), D->getGetterId(), D->getSetterId());
+
+  SemaRef.InstantiateAttrs(TemplateArgs, D, Property, LateAttrs,
+                           StartingScope);
+
+  if (Invalid)
+    Property->setInvalidDecl();
+
+  Property->setAccess(D->getAccess());
+  Owner->addDecl(Property);
+
+  return Property;
+}
+
+Decl *TemplateDeclInstantiator::VisitIndirectFieldDecl(IndirectFieldDecl *D) {
+  NamedDecl **NamedChain =
+    new (SemaRef.Context)NamedDecl*[D->getChainingSize()];
+
+  int i = 0;
+  for (auto *PI : D->chain()) {
+    NamedDecl *Next = SemaRef.FindInstantiatedDecl(D->getLocation(), PI,
+                                              TemplateArgs);
+    if (!Next)
+      return nullptr;
+
+    NamedChain[i++] = Next;
+  }
+
+  QualType T = cast<FieldDecl>(NamedChain[i-1])->getType();
+  IndirectFieldDecl *IndirectField = IndirectFieldDecl::Create(
+      SemaRef.Context, Owner, D->getLocation(), D->getIdentifier(), T,
+      {NamedChain, D->getChainingSize()});
+
+  for (const auto *Attr : D->attrs())
+    IndirectField->addAttr(Attr->clone(SemaRef.Context));
+
+  IndirectField->setImplicit(D->isImplicit());
+  IndirectField->setAccess(D->getAccess());
+  Owner->addDecl(IndirectField);
+  return IndirectField;
+}
+
+Decl *TemplateDeclInstantiator::VisitFriendDecl(FriendDecl *D) {
+  // Handle friend type expressions by simply substituting template
+  // parameters into the pattern type and checking the result.
+  if (TypeSourceInfo *Ty = D->getFriendType()) {
+    TypeSourceInfo *InstTy;
+    // If this is an unsupported friend, don't bother substituting template
+    // arguments into it. The actual type referred to won't be used by any
+    // parts of Clang, and may not be valid for instantiating. Just use the
+    // same info for the instantiated friend.
+    if (D->isUnsupportedFriend()) {
+      InstTy = Ty;
+    } else {
+      InstTy = SemaRef.SubstType(Ty, TemplateArgs,
+                                 D->getLocation(), DeclarationName());
+    }
+    if (!InstTy)
+      return nullptr;
+
+    FriendDecl *FD = SemaRef.CheckFriendTypeDecl(D->getBeginLoc(),
+                                                 D->getFriendLoc(), InstTy);
+    if (!FD)
+      return nullptr;
+
+    FD->setAccess(AS_public);
+    FD->setUnsupportedFriend(D->isUnsupportedFriend());
+    Owner->addDecl(FD);
+    return FD;
+  }
+
+  NamedDecl *ND = D->getFriendDecl();
+  assert(ND && "friend decl must be a decl or a type!");
+
+  // All of the Visit implementations for the various potential friend
+  // declarations have to be carefully written to work for friend
+  // objects, with the most important detail being that the target
+  // decl should almost certainly not be placed in Owner.
+  Decl *NewND = Visit(ND);
+  if (!NewND) return nullptr;
+
+  FriendDecl *FD =
+    FriendDecl::Create(SemaRef.Context, Owner, D->getLocation(),
+                       cast<NamedDecl>(NewND), D->getFriendLoc());
+  FD->setAccess(AS_public);
+  FD->setUnsupportedFriend(D->isUnsupportedFriend());
+  Owner->addDecl(FD);
+  return FD;
+}
+
+Decl *TemplateDeclInstantiator::VisitStaticAssertDecl(StaticAssertDecl *D) {
+  Expr *AssertExpr = D->getAssertExpr();
+
+  // The expression in a static assertion is a constant expression.
+  EnterExpressionEvaluationContext Unevaluated(
+      SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+
+  ExprResult InstantiatedAssertExpr
+    = SemaRef.SubstExpr(AssertExpr, TemplateArgs);
+  if (InstantiatedAssertExpr.isInvalid())
+    return nullptr;
+
+  return SemaRef.BuildStaticAssertDeclaration(D->getLocation(),
+                                              InstantiatedAssertExpr.get(),
+                                              D->getMessage(),
+                                              D->getRParenLoc(),
+                                              D->isFailed());
+}
+
+Decl *TemplateDeclInstantiator::VisitEnumDecl(EnumDecl *D) {
+  EnumDecl *PrevDecl = nullptr;
+  if (EnumDecl *PatternPrev = getPreviousDeclForInstantiation(D)) {
+    NamedDecl *Prev = SemaRef.FindInstantiatedDecl(D->getLocation(),
+                                                   PatternPrev,
+                                                   TemplateArgs);
+    if (!Prev) return nullptr;
+    PrevDecl = cast<EnumDecl>(Prev);
+  }
+
+  EnumDecl *Enum =
+      EnumDecl::Create(SemaRef.Context, Owner, D->getBeginLoc(),
+                       D->getLocation(), D->getIdentifier(), PrevDecl,
+                       D->isScoped(), D->isScopedUsingClassTag(), D->isFixed());
+  if (D->isFixed()) {
+    if (TypeSourceInfo *TI = D->getIntegerTypeSourceInfo()) {
+      // If we have type source information for the underlying type, it means it
+      // has been explicitly set by the user. Perform substitution on it before
+      // moving on.
+      SourceLocation UnderlyingLoc = TI->getTypeLoc().getBeginLoc();
+      TypeSourceInfo *NewTI = SemaRef.SubstType(TI, TemplateArgs, UnderlyingLoc,
+                                                DeclarationName());
+      if (!NewTI || SemaRef.CheckEnumUnderlyingType(NewTI))
+        Enum->setIntegerType(SemaRef.Context.IntTy);
+      else
+        Enum->setIntegerTypeSourceInfo(NewTI);
+    } else {
+      assert(!D->getIntegerType()->isDependentType()
+             && "Dependent type without type source info");
+      Enum->setIntegerType(D->getIntegerType());
+    }
+  }
+
+  SemaRef.InstantiateAttrs(TemplateArgs, D, Enum);
+
+  Enum->setInstantiationOfMemberEnum(D, TSK_ImplicitInstantiation);
+  Enum->setAccess(D->getAccess());
+  // Forward the mangling number from the template to the instantiated decl.
+  SemaRef.Context.setManglingNumber(Enum, SemaRef.Context.getManglingNumber(D));
+  // See if the old tag was defined along with a declarator.
+  // If it did, mark the new tag as being associated with that declarator.
+  if (DeclaratorDecl *DD = SemaRef.Context.getDeclaratorForUnnamedTagDecl(D))
+    SemaRef.Context.addDeclaratorForUnnamedTagDecl(Enum, DD);
+  // See if the old tag was defined along with a typedef.
+  // If it did, mark the new tag as being associated with that typedef.
+  if (TypedefNameDecl *TND = SemaRef.Context.getTypedefNameForUnnamedTagDecl(D))
+    SemaRef.Context.addTypedefNameForUnnamedTagDecl(Enum, TND);
+  if (SubstQualifier(D, Enum)) return nullptr;
+  Owner->addDecl(Enum);
+
+  EnumDecl *Def = D->getDefinition();
+  if (Def && Def != D) {
+    // If this is an out-of-line definition of an enum member template, check
+    // that the underlying types match in the instantiation of both
+    // declarations.
+    if (TypeSourceInfo *TI = Def->getIntegerTypeSourceInfo()) {
+      SourceLocation UnderlyingLoc = TI->getTypeLoc().getBeginLoc();
+      QualType DefnUnderlying =
+        SemaRef.SubstType(TI->getType(), TemplateArgs,
+                          UnderlyingLoc, DeclarationName());
+      SemaRef.CheckEnumRedeclaration(Def->getLocation(), Def->isScoped(),
+                                     DefnUnderlying, /*IsFixed=*/true, Enum);
+    }
+  }
+
+  // C++11 [temp.inst]p1: The implicit instantiation of a class template
+  // specialization causes the implicit instantiation of the declarations, but
+  // not the definitions of scoped member enumerations.
+  //
+  // DR1484 clarifies that enumeration definitions inside of a template
+  // declaration aren't considered entities that can be separately instantiated
+  // from the rest of the entity they are declared inside of.
+  if (isDeclWithinFunction(D) ? D == Def : Def && !Enum->isScoped()) {
+    SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Enum);
+    InstantiateEnumDefinition(Enum, Def);
+  }
+
+  return Enum;
+}
+
+void TemplateDeclInstantiator::InstantiateEnumDefinition(
+    EnumDecl *Enum, EnumDecl *Pattern) {
+  Enum->startDefinition();
+
+  // Update the location to refer to the definition.
+  Enum->setLocation(Pattern->getLocation());
+
+  SmallVector<Decl*, 4> Enumerators;
+
+  EnumConstantDecl *LastEnumConst = nullptr;
+  for (auto *EC : Pattern->enumerators()) {
+    // The specified value for the enumerator.
+    ExprResult Value((Expr *)nullptr);
+    if (Expr *UninstValue = EC->getInitExpr()) {
+      // The enumerator's value expression is a constant expression.
+      EnterExpressionEvaluationContext Unevaluated(
+          SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+
+      Value = SemaRef.SubstExpr(UninstValue, TemplateArgs);
+    }
+
+    // Drop the initial value and continue.
+    bool isInvalid = false;
+    if (Value.isInvalid()) {
+      Value = nullptr;
+      isInvalid = true;
+    }
+
+    EnumConstantDecl *EnumConst
+      = SemaRef.CheckEnumConstant(Enum, LastEnumConst,
+                                  EC->getLocation(), EC->getIdentifier(),
+                                  Value.get());
+
+    if (isInvalid) {
+      if (EnumConst)
+        EnumConst->setInvalidDecl();
+      Enum->setInvalidDecl();
+    }
+
+    if (EnumConst) {
+      SemaRef.InstantiateAttrs(TemplateArgs, EC, EnumConst);
+
+      EnumConst->setAccess(Enum->getAccess());
+      Enum->addDecl(EnumConst);
+      Enumerators.push_back(EnumConst);
+      LastEnumConst = EnumConst;
+
+      if (Pattern->getDeclContext()->isFunctionOrMethod() &&
+          !Enum->isScoped()) {
+        // If the enumeration is within a function or method, record the enum
+        // constant as a local.
+        SemaRef.CurrentInstantiationScope->InstantiatedLocal(EC, EnumConst);
+      }
+    }
+  }
+
+  SemaRef.ActOnEnumBody(Enum->getLocation(), Enum->getBraceRange(), Enum,
+                        Enumerators, nullptr, ParsedAttributesView());
+}
+
+Decl *TemplateDeclInstantiator::VisitEnumConstantDecl(EnumConstantDecl *D) {
+  llvm_unreachable("EnumConstantDecls can only occur within EnumDecls.");
+}
+
+Decl *
+TemplateDeclInstantiator::VisitBuiltinTemplateDecl(BuiltinTemplateDecl *D) {
+  llvm_unreachable("BuiltinTemplateDecls cannot be instantiated.");
+}
+
+Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
+  bool isFriend = (D->getFriendObjectKind() != Decl::FOK_None);
+
+  // Create a local instantiation scope for this class template, which
+  // will contain the instantiations of the template parameters.
+  LocalInstantiationScope Scope(SemaRef);
+  TemplateParameterList *TempParams = D->getTemplateParameters();
+  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
+  if (!InstParams)
+    return nullptr;
+
+  CXXRecordDecl *Pattern = D->getTemplatedDecl();
+
+  // Instantiate the qualifier.  We have to do this first in case
+  // we're a friend declaration, because if we are then we need to put
+  // the new declaration in the appropriate context.
+  NestedNameSpecifierLoc QualifierLoc = Pattern->getQualifierLoc();
+  if (QualifierLoc) {
+    QualifierLoc = SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc,
+                                                       TemplateArgs);
+    if (!QualifierLoc)
+      return nullptr;
+  }
+
+  CXXRecordDecl *PrevDecl = nullptr;
+  ClassTemplateDecl *PrevClassTemplate = nullptr;
+
+  if (!isFriend && getPreviousDeclForInstantiation(Pattern)) {
+    DeclContext::lookup_result Found = Owner->lookup(Pattern->getDeclName());
+    if (!Found.empty()) {
+      PrevClassTemplate = dyn_cast<ClassTemplateDecl>(Found.front());
+      if (PrevClassTemplate)
+        PrevDecl = PrevClassTemplate->getTemplatedDecl();
+    }
+  }
+
+  // If this isn't a friend, then it's a member template, in which
+  // case we just want to build the instantiation in the
+  // specialization.  If it is a friend, we want to build it in
+  // the appropriate context.
+  DeclContext *DC = Owner;
+  if (isFriend) {
+    if (QualifierLoc) {
+      CXXScopeSpec SS;
+      SS.Adopt(QualifierLoc);
+      DC = SemaRef.computeDeclContext(SS);
+      if (!DC) return nullptr;
+    } else {
+      DC = SemaRef.FindInstantiatedContext(Pattern->getLocation(),
+                                           Pattern->getDeclContext(),
+                                           TemplateArgs);
+    }
+
+    // Look for a previous declaration of the template in the owning
+    // context.
+    LookupResult R(SemaRef, Pattern->getDeclName(), Pattern->getLocation(),
+                   Sema::LookupOrdinaryName,
+                   SemaRef.forRedeclarationInCurContext());
+    SemaRef.LookupQualifiedName(R, DC);
+
+    if (R.isSingleResult()) {
+      PrevClassTemplate = R.getAsSingle<ClassTemplateDecl>();
+      if (PrevClassTemplate)
+        PrevDecl = PrevClassTemplate->getTemplatedDecl();
+    }
+
+    if (!PrevClassTemplate && QualifierLoc) {
+      SemaRef.Diag(Pattern->getLocation(), diag::err_not_tag_in_scope)
+        << D->getTemplatedDecl()->getTagKind() << Pattern->getDeclName() << DC
+        << QualifierLoc.getSourceRange();
+      return nullptr;
+    }
+
+    bool AdoptedPreviousTemplateParams = false;
+    if (PrevClassTemplate) {
+      bool Complain = true;
+
+      // HACK: libstdc++ 4.2.1 contains an ill-formed friend class
+      // template for struct std::tr1::__detail::_Map_base, where the
+      // template parameters of the friend declaration don't match the
+      // template parameters of the original declaration. In this one
+      // case, we don't complain about the ill-formed friend
+      // declaration.
+      if (isFriend && Pattern->getIdentifier() &&
+          Pattern->getIdentifier()->isStr("_Map_base") &&
+          DC->isNamespace() &&
+          cast<NamespaceDecl>(DC)->getIdentifier() &&
+          cast<NamespaceDecl>(DC)->getIdentifier()->isStr("__detail")) {
+        DeclContext *DCParent = DC->getParent();
+        if (DCParent->isNamespace() &&
+            cast<NamespaceDecl>(DCParent)->getIdentifier() &&
+            cast<NamespaceDecl>(DCParent)->getIdentifier()->isStr("tr1")) {
+          if (cast<Decl>(DCParent)->isInStdNamespace())
+            Complain = false;
+        }
+      }
+
+      TemplateParameterList *PrevParams
+        = PrevClassTemplate->getMostRecentDecl()->getTemplateParameters();
+
+      // Make sure the parameter lists match.
+      if (!SemaRef.TemplateParameterListsAreEqual(InstParams, PrevParams,
+                                                  Complain,
+                                                  Sema::TPL_TemplateMatch)) {
+        if (Complain)
+          return nullptr;
+
+        AdoptedPreviousTemplateParams = true;
+        InstParams = PrevParams;
+      }
+
+      // Do some additional validation, then merge default arguments
+      // from the existing declarations.
+      if (!AdoptedPreviousTemplateParams &&
+          SemaRef.CheckTemplateParameterList(InstParams, PrevParams,
+                                             Sema::TPC_ClassTemplate))
+        return nullptr;
+    }
+  }
+
+  CXXRecordDecl *RecordInst = CXXRecordDecl::Create(
+      SemaRef.Context, Pattern->getTagKind(), DC, Pattern->getBeginLoc(),
+      Pattern->getLocation(), Pattern->getIdentifier(), PrevDecl,
+      /*DelayTypeCreation=*/true);
+
+  if (QualifierLoc)
+    RecordInst->setQualifierInfo(QualifierLoc);
+
+  SemaRef.InstantiateAttrsForDecl(TemplateArgs, Pattern, RecordInst, LateAttrs,
+                                                              StartingScope);
+
+  ClassTemplateDecl *Inst
+    = ClassTemplateDecl::Create(SemaRef.Context, DC, D->getLocation(),
+                                D->getIdentifier(), InstParams, RecordInst);
+  assert(!(isFriend && Owner->isDependentContext()));
+  Inst->setPreviousDecl(PrevClassTemplate);
+
+  RecordInst->setDescribedClassTemplate(Inst);
+
+  if (isFriend) {
+    if (PrevClassTemplate)
+      Inst->setAccess(PrevClassTemplate->getAccess());
+    else
+      Inst->setAccess(D->getAccess());
+
+    Inst->setObjectOfFriendDecl();
+    // TODO: do we want to track the instantiation progeny of this
+    // friend target decl?
+  } else {
+    Inst->setAccess(D->getAccess());
+    if (!PrevClassTemplate)
+      Inst->setInstantiatedFromMemberTemplate(D);
+  }
+
+  // Trigger creation of the type for the instantiation.
+  SemaRef.Context.getInjectedClassNameType(RecordInst,
+                                    Inst->getInjectedClassNameSpecialization());
+
+  // Finish handling of friends.
+  if (isFriend) {
+    DC->makeDeclVisibleInContext(Inst);
+    Inst->setLexicalDeclContext(Owner);
+    RecordInst->setLexicalDeclContext(Owner);
+    return Inst;
+  }
+
+  if (D->isOutOfLine()) {
+    Inst->setLexicalDeclContext(D->getLexicalDeclContext());
+    RecordInst->setLexicalDeclContext(D->getLexicalDeclContext());
+  }
+
+  Owner->addDecl(Inst);
+
+  if (!PrevClassTemplate) {
+    // Queue up any out-of-line partial specializations of this member
+    // class template; the client will force their instantiation once
+    // the enclosing class has been instantiated.
+    SmallVector<ClassTemplatePartialSpecializationDecl *, 4> PartialSpecs;
+    D->getPartialSpecializations(PartialSpecs);
+    for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I)
+      if (PartialSpecs[I]->getFirstDecl()->isOutOfLine())
+        OutOfLinePartialSpecs.push_back(std::make_pair(Inst, PartialSpecs[I]));
+  }
+
+  return Inst;
+}
+
+Decl *
+TemplateDeclInstantiator::VisitClassTemplatePartialSpecializationDecl(
+                                   ClassTemplatePartialSpecializationDecl *D) {
+  ClassTemplateDecl *ClassTemplate = D->getSpecializedTemplate();
+
+  // Lookup the already-instantiated declaration in the instantiation
+  // of the class template and return that.
+  DeclContext::lookup_result Found
+    = Owner->lookup(ClassTemplate->getDeclName());
+  if (Found.empty())
+    return nullptr;
+
+  ClassTemplateDecl *InstClassTemplate
+    = dyn_cast<ClassTemplateDecl>(Found.front());
+  if (!InstClassTemplate)
+    return nullptr;
+
+  if (ClassTemplatePartialSpecializationDecl *Result
+        = InstClassTemplate->findPartialSpecInstantiatedFromMember(D))
+    return Result;
+
+  return InstantiateClassTemplatePartialSpecialization(InstClassTemplate, D);
+}
+
+Decl *TemplateDeclInstantiator::VisitVarTemplateDecl(VarTemplateDecl *D) {
+  assert(D->getTemplatedDecl()->isStaticDataMember() &&
+         "Only static data member templates are allowed.");
+
+  // Create a local instantiation scope for this variable template, which
+  // will contain the instantiations of the template parameters.
+  LocalInstantiationScope Scope(SemaRef);
+  TemplateParameterList *TempParams = D->getTemplateParameters();
+  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
+  if (!InstParams)
+    return nullptr;
+
+  VarDecl *Pattern = D->getTemplatedDecl();
+  VarTemplateDecl *PrevVarTemplate = nullptr;
+
+  if (getPreviousDeclForInstantiation(Pattern)) {
+    DeclContext::lookup_result Found = Owner->lookup(Pattern->getDeclName());
+    if (!Found.empty())
+      PrevVarTemplate = dyn_cast<VarTemplateDecl>(Found.front());
+  }
+
+  VarDecl *VarInst =
+      cast_or_null<VarDecl>(VisitVarDecl(Pattern,
+                                         /*InstantiatingVarTemplate=*/true));
+  if (!VarInst) return nullptr;
+
+  DeclContext *DC = Owner;
+
+  VarTemplateDecl *Inst = VarTemplateDecl::Create(
+      SemaRef.Context, DC, D->getLocation(), D->getIdentifier(), InstParams,
+      VarInst);
+  VarInst->setDescribedVarTemplate(Inst);
+  Inst->setPreviousDecl(PrevVarTemplate);
+
+  Inst->setAccess(D->getAccess());
+  if (!PrevVarTemplate)
+    Inst->setInstantiatedFromMemberTemplate(D);
+
+  if (D->isOutOfLine()) {
+    Inst->setLexicalDeclContext(D->getLexicalDeclContext());
+    VarInst->setLexicalDeclContext(D->getLexicalDeclContext());
+  }
+
+  Owner->addDecl(Inst);
+
+  if (!PrevVarTemplate) {
+    // Queue up any out-of-line partial specializations of this member
+    // variable template; the client will force their instantiation once
+    // the enclosing class has been instantiated.
+    SmallVector<VarTemplatePartialSpecializationDecl *, 4> PartialSpecs;
+    D->getPartialSpecializations(PartialSpecs);
+    for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I)
+      if (PartialSpecs[I]->getFirstDecl()->isOutOfLine())
+        OutOfLineVarPartialSpecs.push_back(
+            std::make_pair(Inst, PartialSpecs[I]));
+  }
+
+  return Inst;
+}
+
+Decl *TemplateDeclInstantiator::VisitVarTemplatePartialSpecializationDecl(
+    VarTemplatePartialSpecializationDecl *D) {
+  assert(D->isStaticDataMember() &&
+         "Only static data member templates are allowed.");
+
+  VarTemplateDecl *VarTemplate = D->getSpecializedTemplate();
+
+  // Lookup the already-instantiated declaration and return that.
+  DeclContext::lookup_result Found = Owner->lookup(VarTemplate->getDeclName());
+  assert(!Found.empty() && "Instantiation found nothing?");
+
+  VarTemplateDecl *InstVarTemplate = dyn_cast<VarTemplateDecl>(Found.front());
+  assert(InstVarTemplate && "Instantiation did not find a variable template?");
+
+  if (VarTemplatePartialSpecializationDecl *Result =
+          InstVarTemplate->findPartialSpecInstantiatedFromMember(D))
+    return Result;
+
+  return InstantiateVarTemplatePartialSpecialization(InstVarTemplate, D);
+}
+
+Decl *
+TemplateDeclInstantiator::VisitFunctionTemplateDecl(FunctionTemplateDecl *D) {
+  // Create a local instantiation scope for this function template, which
+  // will contain the instantiations of the template parameters and then get
+  // merged with the local instantiation scope for the function template
+  // itself.
+  LocalInstantiationScope Scope(SemaRef);
+
+  TemplateParameterList *TempParams = D->getTemplateParameters();
+  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
+  if (!InstParams)
+    return nullptr;
+
+  FunctionDecl *Instantiated = nullptr;
+  if (CXXMethodDecl *DMethod = dyn_cast<CXXMethodDecl>(D->getTemplatedDecl()))
+    Instantiated = cast_or_null<FunctionDecl>(VisitCXXMethodDecl(DMethod,
+                                                                 InstParams));
+  else
+    Instantiated = cast_or_null<FunctionDecl>(VisitFunctionDecl(
+                                                          D->getTemplatedDecl(),
+                                                                InstParams));
+
+  if (!Instantiated)
+    return nullptr;
+
+  // Link the instantiated function template declaration to the function
+  // template from which it was instantiated.
+  FunctionTemplateDecl *InstTemplate
+    = Instantiated->getDescribedFunctionTemplate();
+  InstTemplate->setAccess(D->getAccess());
+  assert(InstTemplate &&
+         "VisitFunctionDecl/CXXMethodDecl didn't create a template!");
+
+  bool isFriend = (InstTemplate->getFriendObjectKind() != Decl::FOK_None);
+
+  // Link the instantiation back to the pattern *unless* this is a
+  // non-definition friend declaration.
+  if (!InstTemplate->getInstantiatedFromMemberTemplate() &&
+      !(isFriend && !D->getTemplatedDecl()->isThisDeclarationADefinition()))
+    InstTemplate->setInstantiatedFromMemberTemplate(D);
+
+  // Make declarations visible in the appropriate context.
+  if (!isFriend) {
+    Owner->addDecl(InstTemplate);
+  } else if (InstTemplate->getDeclContext()->isRecord() &&
+             !getPreviousDeclForInstantiation(D)) {
+    SemaRef.CheckFriendAccess(InstTemplate);
+  }
+
+  return InstTemplate;
+}
+
+Decl *TemplateDeclInstantiator::VisitCXXRecordDecl(CXXRecordDecl *D) {
+  CXXRecordDecl *PrevDecl = nullptr;
+  if (D->isInjectedClassName())
+    PrevDecl = cast<CXXRecordDecl>(Owner);
+  else if (CXXRecordDecl *PatternPrev = getPreviousDeclForInstantiation(D)) {
+    NamedDecl *Prev = SemaRef.FindInstantiatedDecl(D->getLocation(),
+                                                   PatternPrev,
+                                                   TemplateArgs);
+    if (!Prev) return nullptr;
+    PrevDecl = cast<CXXRecordDecl>(Prev);
+  }
+
+  CXXRecordDecl *Record = CXXRecordDecl::Create(
+      SemaRef.Context, D->getTagKind(), Owner, D->getBeginLoc(),
+      D->getLocation(), D->getIdentifier(), PrevDecl);
+
+  // Substitute the nested name specifier, if any.
+  if (SubstQualifier(D, Record))
+    return nullptr;
+
+  SemaRef.InstantiateAttrsForDecl(TemplateArgs, D, Record, LateAttrs,
+                                                              StartingScope);
+
+  Record->setImplicit(D->isImplicit());
+  // FIXME: Check against AS_none is an ugly hack to work around the issue that
+  // the tag decls introduced by friend class declarations don't have an access
+  // specifier. Remove once this area of the code gets sorted out.
+  if (D->getAccess() != AS_none)
+    Record->setAccess(D->getAccess());
+  if (!D->isInjectedClassName())
+    Record->setInstantiationOfMemberClass(D, TSK_ImplicitInstantiation);
+
+  // If the original function was part of a friend declaration,
+  // inherit its namespace state.
+  if (D->getFriendObjectKind())
+    Record->setObjectOfFriendDecl();
+
+  // Make sure that anonymous structs and unions are recorded.
+  if (D->isAnonymousStructOrUnion())
+    Record->setAnonymousStructOrUnion(true);
+
+  if (D->isLocalClass())
+    SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Record);
+
+  // Forward the mangling number from the template to the instantiated decl.
+  SemaRef.Context.setManglingNumber(Record,
+                                    SemaRef.Context.getManglingNumber(D));
+
+  // See if the old tag was defined along with a declarator.
+  // If it did, mark the new tag as being associated with that declarator.
+  if (DeclaratorDecl *DD = SemaRef.Context.getDeclaratorForUnnamedTagDecl(D))
+    SemaRef.Context.addDeclaratorForUnnamedTagDecl(Record, DD);
+
+  // See if the old tag was defined along with a typedef.
+  // If it did, mark the new tag as being associated with that typedef.
+  if (TypedefNameDecl *TND = SemaRef.Context.getTypedefNameForUnnamedTagDecl(D))
+    SemaRef.Context.addTypedefNameForUnnamedTagDecl(Record, TND);
+
+  Owner->addDecl(Record);
+
+  // DR1484 clarifies that the members of a local class are instantiated as part
+  // of the instantiation of their enclosing entity.
+  if (D->isCompleteDefinition() && D->isLocalClass()) {
+    Sema::LocalEagerInstantiationScope LocalInstantiations(SemaRef);
+
+    SemaRef.InstantiateClass(D->getLocation(), Record, D, TemplateArgs,
+                             TSK_ImplicitInstantiation,
+                             /*Complain=*/true);
+
+    // For nested local classes, we will instantiate the members when we
+    // reach the end of the outermost (non-nested) local class.
+    if (!D->isCXXClassMember())
+      SemaRef.InstantiateClassMembers(D->getLocation(), Record, TemplateArgs,
+                                      TSK_ImplicitInstantiation);
+
+    // This class may have local implicit instantiations that need to be
+    // performed within this scope.
+    LocalInstantiations.perform();
+  }
+
+  SemaRef.DiagnoseUnusedNestedTypedefs(Record);
+
+  return Record;
+}
+
+/// Adjust the given function type for an instantiation of the
+/// given declaration, to cope with modifications to the function's type that
+/// aren't reflected in the type-source information.
+///
+/// \param D The declaration we're instantiating.
+/// \param TInfo The already-instantiated type.
+static QualType adjustFunctionTypeForInstantiation(ASTContext &Context,
+                                                   FunctionDecl *D,
+                                                   TypeSourceInfo *TInfo) {
+  const FunctionProtoType *OrigFunc
+    = D->getType()->castAs<FunctionProtoType>();
+  const FunctionProtoType *NewFunc
+    = TInfo->getType()->castAs<FunctionProtoType>();
+  if (OrigFunc->getExtInfo() == NewFunc->getExtInfo())
+    return TInfo->getType();
+
+  FunctionProtoType::ExtProtoInfo NewEPI = NewFunc->getExtProtoInfo();
+  NewEPI.ExtInfo = OrigFunc->getExtInfo();
+  return Context.getFunctionType(NewFunc->getReturnType(),
+                                 NewFunc->getParamTypes(), NewEPI);
+}
+
+/// Normal class members are of more specific types and therefore
+/// don't make it here.  This function serves three purposes:
+///   1) instantiating function templates
+///   2) substituting friend declarations
+///   3) substituting deduction guide declarations for nested class templates
+Decl *TemplateDeclInstantiator::VisitFunctionDecl(FunctionDecl *D,
+                                       TemplateParameterList *TemplateParams) {
+  // Check whether there is already a function template specialization for
+  // this declaration.
+  FunctionTemplateDecl *FunctionTemplate = D->getDescribedFunctionTemplate();
+  if (FunctionTemplate && !TemplateParams) {
+    ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();
+
+    void *InsertPos = nullptr;
+    FunctionDecl *SpecFunc
+      = FunctionTemplate->findSpecialization(Innermost, InsertPos);
+
+    // If we already have a function template specialization, return it.
+    if (SpecFunc)
+      return SpecFunc;
+  }
+
+  bool isFriend;
+  if (FunctionTemplate)
+    isFriend = (FunctionTemplate->getFriendObjectKind() != Decl::FOK_None);
+  else
+    isFriend = (D->getFriendObjectKind() != Decl::FOK_None);
+
+  bool MergeWithParentScope = (TemplateParams != nullptr) ||
+    Owner->isFunctionOrMethod() ||
+    !(isa<Decl>(Owner) &&
+      cast<Decl>(Owner)->isDefinedOutsideFunctionOrMethod());
+  LocalInstantiationScope Scope(SemaRef, MergeWithParentScope);
+
+  ExplicitSpecifier InstantiatedExplicitSpecifier;
+  if (auto *DGuide = dyn_cast<CXXDeductionGuideDecl>(D)) {
+    InstantiatedExplicitSpecifier = instantiateExplicitSpecifier(
+        SemaRef, TemplateArgs, DGuide->getExplicitSpecifier(), DGuide);
+    if (InstantiatedExplicitSpecifier.isInvalid())
+      return nullptr;
+  }
+
+  SmallVector<ParmVarDecl *, 4> Params;
+  TypeSourceInfo *TInfo = SubstFunctionType(D, Params);
+  if (!TInfo)
+    return nullptr;
+  QualType T = adjustFunctionTypeForInstantiation(SemaRef.Context, D, TInfo);
+
+  NestedNameSpecifierLoc QualifierLoc = D->getQualifierLoc();
+  if (QualifierLoc) {
+    QualifierLoc = SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc,
+                                                       TemplateArgs);
+    if (!QualifierLoc)
+      return nullptr;
+  }
+
+  // If we're instantiating a local function declaration, put the result
+  // in the enclosing namespace; otherwise we need to find the instantiated
+  // context.
+  DeclContext *DC;
+  if (D->isLocalExternDecl()) {
+    DC = Owner;
+    SemaRef.adjustContextForLocalExternDecl(DC);
+  } else if (isFriend && QualifierLoc) {
+    CXXScopeSpec SS;
+    SS.Adopt(QualifierLoc);
+    DC = SemaRef.computeDeclContext(SS);
+    if (!DC) return nullptr;
+  } else {
+    DC = SemaRef.FindInstantiatedContext(D->getLocation(), D->getDeclContext(),
+                                         TemplateArgs);
+  }
+
+  DeclarationNameInfo NameInfo
+    = SemaRef.SubstDeclarationNameInfo(D->getNameInfo(), TemplateArgs);
+
+  FunctionDecl *Function;
+  if (auto *DGuide = dyn_cast<CXXDeductionGuideDecl>(D)) {
+    Function = CXXDeductionGuideDecl::Create(
+        SemaRef.Context, DC, D->getInnerLocStart(),
+        InstantiatedExplicitSpecifier, NameInfo, T, TInfo,
+        D->getSourceRange().getEnd());
+    if (DGuide->isCopyDeductionCandidate())
+      cast<CXXDeductionGuideDecl>(Function)->setIsCopyDeductionCandidate();
+    Function->setAccess(D->getAccess());
+  } else {
+    Function = FunctionDecl::Create(
+        SemaRef.Context, DC, D->getInnerLocStart(), NameInfo, T, TInfo,
+        D->getCanonicalDecl()->getStorageClass(), D->isInlineSpecified(),
+        D->hasWrittenPrototype(), D->getConstexprKind());
+    Function->setRangeEnd(D->getSourceRange().getEnd());
+  }
+
+  if (D->isInlined())
+    Function->setImplicitlyInline();
+
+  if (QualifierLoc)
+    Function->setQualifierInfo(QualifierLoc);
+
+  if (D->isLocalExternDecl())
+    Function->setLocalExternDecl();
+
+  DeclContext *LexicalDC = Owner;
+  if (!isFriend && D->isOutOfLine() && !D->isLocalExternDecl()) {
+    assert(D->getDeclContext()->isFileContext());
+    LexicalDC = D->getDeclContext();
+  }
+
+  Function->setLexicalDeclContext(LexicalDC);
+
+  // Attach the parameters
+  for (unsigned P = 0; P < Params.size(); ++P)
+    if (Params[P])
+      Params[P]->setOwningFunction(Function);
+  Function->setParams(Params);
+
+  if (TemplateParams) {
+    // Our resulting instantiation is actually a function template, since we
+    // are substituting only the outer template parameters. For example, given
+    //
+    //   template<typename T>
+    //   struct X {
+    //     template<typename U> friend void f(T, U);
+    //   };
+    //
+    //   X<int> x;
+    //
+    // We are instantiating the friend function template "f" within X<int>,
+    // which means substituting int for T, but leaving "f" as a friend function
+    // template.
+    // Build the function template itself.
+    FunctionTemplate = FunctionTemplateDecl::Create(SemaRef.Context, DC,
+                                                    Function->getLocation(),
+                                                    Function->getDeclName(),
+                                                    TemplateParams, Function);
+    Function->setDescribedFunctionTemplate(FunctionTemplate);
+
+    FunctionTemplate->setLexicalDeclContext(LexicalDC);
+
+    if (isFriend && D->isThisDeclarationADefinition()) {
+      FunctionTemplate->setInstantiatedFromMemberTemplate(
+                                           D->getDescribedFunctionTemplate());
+    }
+  } else if (FunctionTemplate) {
+    // Record this function template specialization.
+    ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();
+    Function->setFunctionTemplateSpecialization(FunctionTemplate,
+                            TemplateArgumentList::CreateCopy(SemaRef.Context,
+                                                             Innermost),
+                                                /*InsertPos=*/nullptr);
+  } else if (isFriend && D->isThisDeclarationADefinition()) {
+    // Do not connect the friend to the template unless it's actually a
+    // definition. We don't want non-template functions to be marked as being
+    // template instantiations.
+    Function->setInstantiationOfMemberFunction(D, TSK_ImplicitInstantiation);
+  }
+
+  if (isFriend)
+    Function->setObjectOfFriendDecl();
+
+  if (InitFunctionInstantiation(Function, D))
+    Function->setInvalidDecl();
+
+  bool IsExplicitSpecialization = false;
+
+  LookupResult Previous(
+      SemaRef, Function->getDeclName(), SourceLocation(),
+      D->isLocalExternDecl() ? Sema::LookupRedeclarationWithLinkage
+                             : Sema::LookupOrdinaryName,
+      D->isLocalExternDecl() ? Sema::ForExternalRedeclaration
+                             : SemaRef.forRedeclarationInCurContext());
+
+  if (DependentFunctionTemplateSpecializationInfo *Info
+        = D->getDependentSpecializationInfo()) {
+    assert(isFriend && "non-friend has dependent specialization info?");
+
+    // Instantiate the explicit template arguments.
+    TemplateArgumentListInfo ExplicitArgs(Info->getLAngleLoc(),
+                                          Info->getRAngleLoc());
+    if (SemaRef.Subst(Info->getTemplateArgs(), Info->getNumTemplateArgs(),
+                      ExplicitArgs, TemplateArgs))
+      return nullptr;
+
+    // Map the candidate templates to their instantiations.
+    for (unsigned I = 0, E = Info->getNumTemplates(); I != E; ++I) {
+      Decl *Temp = SemaRef.FindInstantiatedDecl(D->getLocation(),
+                                                Info->getTemplate(I),
+                                                TemplateArgs);
+      if (!Temp) return nullptr;
+
+      Previous.addDecl(cast<FunctionTemplateDecl>(Temp));
+    }
+
+    if (SemaRef.CheckFunctionTemplateSpecialization(Function,
+                                                    &ExplicitArgs,
+                                                    Previous))
+      Function->setInvalidDecl();
+
+    IsExplicitSpecialization = true;
+  } else if (const ASTTemplateArgumentListInfo *Info =
+                 D->getTemplateSpecializationArgsAsWritten()) {
+    // The name of this function was written as a template-id.
+    SemaRef.LookupQualifiedName(Previous, DC);
+
+    // Instantiate the explicit template arguments.
+    TemplateArgumentListInfo ExplicitArgs(Info->getLAngleLoc(),
+                                          Info->getRAngleLoc());
+    if (SemaRef.Subst(Info->getTemplateArgs(), Info->getNumTemplateArgs(),
+                      ExplicitArgs, TemplateArgs))
+      return nullptr;
+
+    if (SemaRef.CheckFunctionTemplateSpecialization(Function,
+                                                    &ExplicitArgs,
+                                                    Previous))
+      Function->setInvalidDecl();
+
+    IsExplicitSpecialization = true;
+  } else if (TemplateParams || !FunctionTemplate) {
+    // Look only into the namespace where the friend would be declared to
+    // find a previous declaration. This is the innermost enclosing namespace,
+    // as described in ActOnFriendFunctionDecl.
+    SemaRef.LookupQualifiedName(Previous, DC);
+
+    // In C++, the previous declaration we find might be a tag type
+    // (class or enum). In this case, the new declaration will hide the
+    // tag type. Note that this does does not apply if we're declaring a
+    // typedef (C++ [dcl.typedef]p4).
+    if (Previous.isSingleTagDecl())
+      Previous.clear();
+  }
+
+  SemaRef.CheckFunctionDeclaration(/*Scope*/ nullptr, Function, Previous,
+                                   IsExplicitSpecialization);
+
+  NamedDecl *PrincipalDecl = (TemplateParams
+                              ? cast<NamedDecl>(FunctionTemplate)
+                              : Function);
+
+  // If the original function was part of a friend declaration,
+  // inherit its namespace state and add it to the owner.
+  if (isFriend) {
+    Function->setObjectOfFriendDecl();
+    if (FunctionTemplateDecl *FT = Function->getDescribedFunctionTemplate())
+      FT->setObjectOfFriendDecl();
+    DC->makeDeclVisibleInContext(PrincipalDecl);
+
+    bool QueuedInstantiation = false;
+
+    // C++11 [temp.friend]p4 (DR329):
+    //   When a function is defined in a friend function declaration in a class
+    //   template, the function is instantiated when the function is odr-used.
+    //   The same restrictions on multiple declarations and definitions that
+    //   apply to non-template function declarations and definitions also apply
+    //   to these implicit definitions.
+    if (D->isThisDeclarationADefinition()) {
+      SemaRef.CheckForFunctionRedefinition(Function);
+      if (!Function->isInvalidDecl()) {
+        for (auto R : Function->redecls()) {
+          if (R == Function)
+            continue;
+
+          // If some prior declaration of this function has been used, we need
+          // to instantiate its definition.
+          if (!QueuedInstantiation && R->isUsed(false)) {
+            if (MemberSpecializationInfo *MSInfo =
+                Function->getMemberSpecializationInfo()) {
+              if (MSInfo->getPointOfInstantiation().isInvalid()) {
+                SourceLocation Loc = R->getLocation(); // FIXME
+                MSInfo->setPointOfInstantiation(Loc);
+                SemaRef.PendingLocalImplicitInstantiations.push_back(
+                    std::make_pair(Function, Loc));
+                QueuedInstantiation = true;
+              }
+            }
+          }
+        }
+      }
+    }
+
+    // Check the template parameter list against the previous declaration. The
+    // goal here is to pick up default arguments added since the friend was
+    // declared; we know the template parameter lists match, since otherwise
+    // we would not have picked this template as the previous declaration.
+    if (TemplateParams && FunctionTemplate->getPreviousDecl()) {
+      SemaRef.CheckTemplateParameterList(
+          TemplateParams,
+          FunctionTemplate->getPreviousDecl()->getTemplateParameters(),
+          Function->isThisDeclarationADefinition()
+              ? Sema::TPC_FriendFunctionTemplateDefinition
+              : Sema::TPC_FriendFunctionTemplate);
+    }
+  }
+
+  if (Function->isLocalExternDecl() && !Function->getPreviousDecl())
+    DC->makeDeclVisibleInContext(PrincipalDecl);
+
+  if (Function->isOverloadedOperator() && !DC->isRecord() &&
+      PrincipalDecl->isInIdentifierNamespace(Decl::IDNS_Ordinary))
+    PrincipalDecl->setNonMemberOperator();
+
+  assert(!D->isDefaulted() && "only methods should be defaulted");
+  return Function;
+}
+
+Decl *TemplateDeclInstantiator::VisitCXXMethodDecl(
+    CXXMethodDecl *D, TemplateParameterList *TemplateParams,
+    Optional<const ASTTemplateArgumentListInfo *>
+        ClassScopeSpecializationArgs) {
+  FunctionTemplateDecl *FunctionTemplate = D->getDescribedFunctionTemplate();
+  if (FunctionTemplate && !TemplateParams) {
+    // We are creating a function template specialization from a function
+    // template. Check whether there is already a function template
+    // specialization for this particular set of template arguments.
+    ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();
+
+    void *InsertPos = nullptr;
+    FunctionDecl *SpecFunc
+      = FunctionTemplate->findSpecialization(Innermost, InsertPos);
+
+    // If we already have a function template specialization, return it.
+    if (SpecFunc)
+      return SpecFunc;
+  }
+
+  bool isFriend;
+  if (FunctionTemplate)
+    isFriend = (FunctionTemplate->getFriendObjectKind() != Decl::FOK_None);
+  else
+    isFriend = (D->getFriendObjectKind() != Decl::FOK_None);
+
+  bool MergeWithParentScope = (TemplateParams != nullptr) ||
+    !(isa<Decl>(Owner) &&
+      cast<Decl>(Owner)->isDefinedOutsideFunctionOrMethod());
+  LocalInstantiationScope Scope(SemaRef, MergeWithParentScope);
+
+  // Instantiate enclosing template arguments for friends.
+  SmallVector<TemplateParameterList *, 4> TempParamLists;
+  unsigned NumTempParamLists = 0;
+  if (isFriend && (NumTempParamLists = D->getNumTemplateParameterLists())) {
+    TempParamLists.resize(NumTempParamLists);
+    for (unsigned I = 0; I != NumTempParamLists; ++I) {
+      TemplateParameterList *TempParams = D->getTemplateParameterList(I);
+      TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
+      if (!InstParams)
+        return nullptr;
+      TempParamLists[I] = InstParams;
+    }
+  }
+
+  ExplicitSpecifier InstantiatedExplicitSpecifier =
+      instantiateExplicitSpecifier(SemaRef, TemplateArgs,
+                                   ExplicitSpecifier::getFromDecl(D), D);
+  if (InstantiatedExplicitSpecifier.isInvalid())
+    return nullptr;
+
+  SmallVector<ParmVarDecl *, 4> Params;
+  TypeSourceInfo *TInfo = SubstFunctionType(D, Params);
+  if (!TInfo)
+    return nullptr;
+  QualType T = adjustFunctionTypeForInstantiation(SemaRef.Context, D, TInfo);
+
+  NestedNameSpecifierLoc QualifierLoc = D->getQualifierLoc();
+  if (QualifierLoc) {
+    QualifierLoc = SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc,
+                                                 TemplateArgs);
+    if (!QualifierLoc)
+      return nullptr;
+  }
+
+  DeclContext *DC = Owner;
+  if (isFriend) {
+    if (QualifierLoc) {
+      CXXScopeSpec SS;
+      SS.Adopt(QualifierLoc);
+      DC = SemaRef.computeDeclContext(SS);
+
+      if (DC && SemaRef.RequireCompleteDeclContext(SS, DC))
+        return nullptr;
+    } else {
+      DC = SemaRef.FindInstantiatedContext(D->getLocation(),
+                                           D->getDeclContext(),
+                                           TemplateArgs);
+    }
+    if (!DC) return nullptr;
+  }
+
+  // Build the instantiated method declaration.
+  CXXRecordDecl *Record = cast<CXXRecordDecl>(DC);
+  CXXMethodDecl *Method = nullptr;
+
+  SourceLocation StartLoc = D->getInnerLocStart();
+  DeclarationNameInfo NameInfo
+    = SemaRef.SubstDeclarationNameInfo(D->getNameInfo(), TemplateArgs);
+  if (CXXConstructorDecl *Constructor = dyn_cast<CXXConstructorDecl>(D)) {
+    Method = CXXConstructorDecl::Create(
+        SemaRef.Context, Record, StartLoc, NameInfo, T, TInfo,
+        InstantiatedExplicitSpecifier, Constructor->isInlineSpecified(), false,
+        Constructor->getConstexprKind());
+    Method->setRangeEnd(Constructor->getEndLoc());
+  } else if (CXXDestructorDecl *Destructor = dyn_cast<CXXDestructorDecl>(D)) {
+    Method = CXXDestructorDecl::Create(SemaRef.Context, Record,
+                                       StartLoc, NameInfo, T, TInfo,
+                                       Destructor->isInlineSpecified(),
+                                       false);
+    Method->setRangeEnd(Destructor->getEndLoc());
+  } else if (CXXConversionDecl *Conversion = dyn_cast<CXXConversionDecl>(D)) {
+    Method = CXXConversionDecl::Create(
+        SemaRef.Context, Record, StartLoc, NameInfo, T, TInfo,
+        Conversion->isInlineSpecified(), InstantiatedExplicitSpecifier,
+        Conversion->getConstexprKind(), Conversion->getEndLoc());
+  } else {
+    StorageClass SC = D->isStatic() ? SC_Static : SC_None;
+    Method = CXXMethodDecl::Create(SemaRef.Context, Record, StartLoc, NameInfo,
+                                   T, TInfo, SC, D->isInlineSpecified(),
+                                   D->getConstexprKind(), D->getEndLoc());
+  }
+
+  if (D->isInlined())
+    Method->setImplicitlyInline();
+
+  if (QualifierLoc)
+    Method->setQualifierInfo(QualifierLoc);
+
+  if (TemplateParams) {
+    // Our resulting instantiation is actually a function template, since we
+    // are substituting only the outer template parameters. For example, given
+    //
+    //   template<typename T>
+    //   struct X {
+    //     template<typename U> void f(T, U);
+    //   };
+    //
+    //   X<int> x;
+    //
+    // We are instantiating the member template "f" within X<int>, which means
+    // substituting int for T, but leaving "f" as a member function template.
+    // Build the function template itself.
+    FunctionTemplate = FunctionTemplateDecl::Create(SemaRef.Context, Record,
+                                                    Method->getLocation(),
+                                                    Method->getDeclName(),
+                                                    TemplateParams, Method);
+    if (isFriend) {
+      FunctionTemplate->setLexicalDeclContext(Owner);
+      FunctionTemplate->setObjectOfFriendDecl();
+    } else if (D->isOutOfLine())
+      FunctionTemplate->setLexicalDeclContext(D->getLexicalDeclContext());
+    Method->setDescribedFunctionTemplate(FunctionTemplate);
+  } else if (FunctionTemplate) {
+    // Record this function template specialization.
+    ArrayRef<TemplateArgument> Innermost = TemplateArgs.getInnermost();
+    Method->setFunctionTemplateSpecialization(FunctionTemplate,
+                         TemplateArgumentList::CreateCopy(SemaRef.Context,
+                                                          Innermost),
+                                              /*InsertPos=*/nullptr);
+  } else if (!isFriend) {
+    // Record that this is an instantiation of a member function.
+    Method->setInstantiationOfMemberFunction(D, TSK_ImplicitInstantiation);
+  }
+
+  // If we are instantiating a member function defined
+  // out-of-line, the instantiation will have the same lexical
+  // context (which will be a namespace scope) as the template.
+  if (isFriend) {
+    if (NumTempParamLists)
+      Method->setTemplateParameterListsInfo(
+          SemaRef.Context,
+          llvm::makeArrayRef(TempParamLists.data(), NumTempParamLists));
+
+    Method->setLexicalDeclContext(Owner);
+    Method->setObjectOfFriendDecl();
+  } else if (D->isOutOfLine())
+    Method->setLexicalDeclContext(D->getLexicalDeclContext());
+
+  // Attach the parameters
+  for (unsigned P = 0; P < Params.size(); ++P)
+    Params[P]->setOwningFunction(Method);
+  Method->setParams(Params);
+
+  if (InitMethodInstantiation(Method, D))
+    Method->setInvalidDecl();
+
+  LookupResult Previous(SemaRef, NameInfo, Sema::LookupOrdinaryName,
+                        Sema::ForExternalRedeclaration);
+
+  bool IsExplicitSpecialization = false;
+
+  // If the name of this function was written as a template-id, instantiate
+  // the explicit template arguments.
+  if (DependentFunctionTemplateSpecializationInfo *Info
+        = D->getDependentSpecializationInfo()) {
+    assert(isFriend && "non-friend has dependent specialization info?");
+
+    // Instantiate the explicit template arguments.
+    TemplateArgumentListInfo ExplicitArgs(Info->getLAngleLoc(),
+                                          Info->getRAngleLoc());
+    if (SemaRef.Subst(Info->getTemplateArgs(), Info->getNumTemplateArgs(),
+                      ExplicitArgs, TemplateArgs))
+      return nullptr;
+
+    // Map the candidate templates to their instantiations.
+    for (unsigned I = 0, E = Info->getNumTemplates(); I != E; ++I) {
+      Decl *Temp = SemaRef.FindInstantiatedDecl(D->getLocation(),
+                                                Info->getTemplate(I),
+                                                TemplateArgs);
+      if (!Temp) return nullptr;
+
+      Previous.addDecl(cast<FunctionTemplateDecl>(Temp));
+    }
+
+    if (SemaRef.CheckFunctionTemplateSpecialization(Method,
+                                                    &ExplicitArgs,
+                                                    Previous))
+      Method->setInvalidDecl();
+
+    IsExplicitSpecialization = true;
+  } else if (const ASTTemplateArgumentListInfo *Info =
+                 ClassScopeSpecializationArgs.getValueOr(
+                     D->getTemplateSpecializationArgsAsWritten())) {
+    SemaRef.LookupQualifiedName(Previous, DC);
+
+    TemplateArgumentListInfo ExplicitArgs(Info->getLAngleLoc(),
+                                          Info->getRAngleLoc());
+    if (SemaRef.Subst(Info->getTemplateArgs(), Info->getNumTemplateArgs(),
+                      ExplicitArgs, TemplateArgs))
+      return nullptr;
+
+    if (SemaRef.CheckFunctionTemplateSpecialization(Method,
+                                                    &ExplicitArgs,
+                                                    Previous))
+      Method->setInvalidDecl();
+
+    IsExplicitSpecialization = true;
+  } else if (ClassScopeSpecializationArgs) {
+    // Class-scope explicit specialization written without explicit template
+    // arguments.
+    SemaRef.LookupQualifiedName(Previous, DC);
+    if (SemaRef.CheckFunctionTemplateSpecialization(Method, nullptr, Previous))
+      Method->setInvalidDecl();
+
+    IsExplicitSpecialization = true;
+  } else if (!FunctionTemplate || TemplateParams || isFriend) {
+    SemaRef.LookupQualifiedName(Previous, Record);
+
+    // In C++, the previous declaration we find might be a tag type
+    // (class or enum). In this case, the new declaration will hide the
+    // tag type. Note that this does does not apply if we're declaring a
+    // typedef (C++ [dcl.typedef]p4).
+    if (Previous.isSingleTagDecl())
+      Previous.clear();
+  }
+
+  SemaRef.CheckFunctionDeclaration(nullptr, Method, Previous,
+                                   IsExplicitSpecialization);
+
+  if (D->isPure())
+    SemaRef.CheckPureMethod(Method, SourceRange());
+
+  // Propagate access.  For a non-friend declaration, the access is
+  // whatever we're propagating from.  For a friend, it should be the
+  // previous declaration we just found.
+  if (isFriend && Method->getPreviousDecl())
+    Method->setAccess(Method->getPreviousDecl()->getAccess());
+  else
+    Method->setAccess(D->getAccess());
+  if (FunctionTemplate)
+    FunctionTemplate->setAccess(Method->getAccess());
+
+  SemaRef.CheckOverrideControl(Method);
+
+  // If a function is defined as defaulted or deleted, mark it as such now.
+  if (D->isExplicitlyDefaulted())
+    SemaRef.SetDeclDefaulted(Method, Method->getLocation());
+  if (D->isDeletedAsWritten())
+    SemaRef.SetDeclDeleted(Method, Method->getLocation());
+
+  // If this is an explicit specialization, mark the implicitly-instantiated
+  // template specialization as being an explicit specialization too.
+  // FIXME: Is this necessary?
+  if (IsExplicitSpecialization && !isFriend)
+    SemaRef.CompleteMemberSpecialization(Method, Previous);
+
+  // If there's a function template, let our caller handle it.
+  if (FunctionTemplate) {
+    // do nothing
+
+  // Don't hide a (potentially) valid declaration with an invalid one.
+  } else if (Method->isInvalidDecl() && !Previous.empty()) {
+    // do nothing
+
+  // Otherwise, check access to friends and make them visible.
+  } else if (isFriend) {
+    // We only need to re-check access for methods which we didn't
+    // manage to match during parsing.
+    if (!D->getPreviousDecl())
+      SemaRef.CheckFriendAccess(Method);
+
+    Record->makeDeclVisibleInContext(Method);
+
+  // Otherwise, add the declaration.  We don't need to do this for
+  // class-scope specializations because we'll have matched them with
+  // the appropriate template.
+  } else {
+    Owner->addDecl(Method);
+  }
+
+  // PR17480: Honor the used attribute to instantiate member function
+  // definitions
+  if (Method->hasAttr<UsedAttr>()) {
+    if (const auto *A = dyn_cast<CXXRecordDecl>(Owner)) {
+      SourceLocation Loc;
+      if (const MemberSpecializationInfo *MSInfo =
+              A->getMemberSpecializationInfo())
+        Loc = MSInfo->getPointOfInstantiation();
+      else if (const auto *Spec = dyn_cast<ClassTemplateSpecializationDecl>(A))
+        Loc = Spec->getPointOfInstantiation();
+      SemaRef.MarkFunctionReferenced(Loc, Method);
+    }
+  }
+
+  return Method;
+}
+
+Decl *TemplateDeclInstantiator::VisitCXXConstructorDecl(CXXConstructorDecl *D) {
+  return VisitCXXMethodDecl(D);
+}
+
+Decl *TemplateDeclInstantiator::VisitCXXDestructorDecl(CXXDestructorDecl *D) {
+  return VisitCXXMethodDecl(D);
+}
+
+Decl *TemplateDeclInstantiator::VisitCXXConversionDecl(CXXConversionDecl *D) {
+  return VisitCXXMethodDecl(D);
+}
+
+Decl *TemplateDeclInstantiator::VisitParmVarDecl(ParmVarDecl *D) {
+  return SemaRef.SubstParmVarDecl(D, TemplateArgs, /*indexAdjustment*/ 0, None,
+                                  /*ExpectParameterPack=*/ false);
+}
+
+Decl *TemplateDeclInstantiator::VisitTemplateTypeParmDecl(
+                                                    TemplateTypeParmDecl *D) {
+  // TODO: don't always clone when decls are refcounted.
+  assert(D->getTypeForDecl()->isTemplateTypeParmType());
+
+  TemplateTypeParmDecl *Inst = TemplateTypeParmDecl::Create(
+      SemaRef.Context, Owner, D->getBeginLoc(), D->getLocation(),
+      D->getDepth() - TemplateArgs.getNumSubstitutedLevels(), D->getIndex(),
+      D->getIdentifier(), D->wasDeclaredWithTypename(), D->isParameterPack());
+  Inst->setAccess(AS_public);
+
+  if (D->hasDefaultArgument() && !D->defaultArgumentWasInherited()) {
+    TypeSourceInfo *InstantiatedDefaultArg =
+        SemaRef.SubstType(D->getDefaultArgumentInfo(), TemplateArgs,
+                          D->getDefaultArgumentLoc(), D->getDeclName());
+    if (InstantiatedDefaultArg)
+      Inst->setDefaultArgument(InstantiatedDefaultArg);
+  }
+
+  // Introduce this template parameter's instantiation into the instantiation
+  // scope.
+  SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Inst);
+
+  return Inst;
+}
+
+Decl *TemplateDeclInstantiator::VisitNonTypeTemplateParmDecl(
+                                                 NonTypeTemplateParmDecl *D) {
+  // Substitute into the type of the non-type template parameter.
+  TypeLoc TL = D->getTypeSourceInfo()->getTypeLoc();
+  SmallVector<TypeSourceInfo *, 4> ExpandedParameterPackTypesAsWritten;
+  SmallVector<QualType, 4> ExpandedParameterPackTypes;
+  bool IsExpandedParameterPack = false;
+  TypeSourceInfo *DI;
+  QualType T;
+  bool Invalid = false;
+
+  if (D->isExpandedParameterPack()) {
+    // The non-type template parameter pack is an already-expanded pack
+    // expansion of types. Substitute into each of the expanded types.
+    ExpandedParameterPackTypes.reserve(D->getNumExpansionTypes());
+    ExpandedParameterPackTypesAsWritten.reserve(D->getNumExpansionTypes());
+    for (unsigned I = 0, N = D->getNumExpansionTypes(); I != N; ++I) {
+      TypeSourceInfo *NewDI =
+          SemaRef.SubstType(D->getExpansionTypeSourceInfo(I), TemplateArgs,
+                            D->getLocation(), D->getDeclName());
+      if (!NewDI)
+        return nullptr;
+
+      QualType NewT =
+          SemaRef.CheckNonTypeTemplateParameterType(NewDI, D->getLocation());
+      if (NewT.isNull())
+        return nullptr;
+
+      ExpandedParameterPackTypesAsWritten.push_back(NewDI);
+      ExpandedParameterPackTypes.push_back(NewT);
+    }
+
+    IsExpandedParameterPack = true;
+    DI = D->getTypeSourceInfo();
+    T = DI->getType();
+  } else if (D->isPackExpansion()) {
+    // The non-type template parameter pack's type is a pack expansion of types.
+    // Determine whether we need to expand this parameter pack into separate
+    // types.
+    PackExpansionTypeLoc Expansion = TL.castAs<PackExpansionTypeLoc>();
+    TypeLoc Pattern = Expansion.getPatternLoc();
+    SmallVector<UnexpandedParameterPack, 2> Unexpanded;
+    SemaRef.collectUnexpandedParameterPacks(Pattern, Unexpanded);
+
+    // Determine whether the set of unexpanded parameter packs can and should
+    // be expanded.
+    bool Expand = true;
+    bool RetainExpansion = false;
+    Optional<unsigned> OrigNumExpansions
+      = Expansion.getTypePtr()->getNumExpansions();
+    Optional<unsigned> NumExpansions = OrigNumExpansions;
+    if (SemaRef.CheckParameterPacksForExpansion(Expansion.getEllipsisLoc(),
+                                                Pattern.getSourceRange(),
+                                                Unexpanded,
+                                                TemplateArgs,
+                                                Expand, RetainExpansion,
+                                                NumExpansions))
+      return nullptr;
+
+    if (Expand) {
+      for (unsigned I = 0; I != *NumExpansions; ++I) {
+        Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, I);
+        TypeSourceInfo *NewDI = SemaRef.SubstType(Pattern, TemplateArgs,
+                                                  D->getLocation(),
+                                                  D->getDeclName());
+        if (!NewDI)
+          return nullptr;
+
+        QualType NewT =
+            SemaRef.CheckNonTypeTemplateParameterType(NewDI, D->getLocation());
+        if (NewT.isNull())
+          return nullptr;
+
+        ExpandedParameterPackTypesAsWritten.push_back(NewDI);
+        ExpandedParameterPackTypes.push_back(NewT);
+      }
+
+      // Note that we have an expanded parameter pack. The "type" of this
+      // expanded parameter pack is the original expansion type, but callers
+      // will end up using the expanded parameter pack types for type-checking.
+      IsExpandedParameterPack = true;
+      DI = D->getTypeSourceInfo();
+      T = DI->getType();
+    } else {
+      // We cannot fully expand the pack expansion now, so substitute into the
+      // pattern and create a new pack expansion type.
+      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, -1);
+      TypeSourceInfo *NewPattern = SemaRef.SubstType(Pattern, TemplateArgs,
+                                                     D->getLocation(),
+                                                     D->getDeclName());
+      if (!NewPattern)
+        return nullptr;
+
+      SemaRef.CheckNonTypeTemplateParameterType(NewPattern, D->getLocation());
+      DI = SemaRef.CheckPackExpansion(NewPattern, Expansion.getEllipsisLoc(),
+                                      NumExpansions);
+      if (!DI)
+        return nullptr;
+
+      T = DI->getType();
+    }
+  } else {
+    // Simple case: substitution into a parameter that is not a parameter pack.
+    DI = SemaRef.SubstType(D->getTypeSourceInfo(), TemplateArgs,
+                           D->getLocation(), D->getDeclName());
+    if (!DI)
+      return nullptr;
+
+    // Check that this type is acceptable for a non-type template parameter.
+    T = SemaRef.CheckNonTypeTemplateParameterType(DI, D->getLocation());
+    if (T.isNull()) {
+      T = SemaRef.Context.IntTy;
+      Invalid = true;
+    }
+  }
+
+  NonTypeTemplateParmDecl *Param;
+  if (IsExpandedParameterPack)
+    Param = NonTypeTemplateParmDecl::Create(
+        SemaRef.Context, Owner, D->getInnerLocStart(), D->getLocation(),
+        D->getDepth() - TemplateArgs.getNumSubstitutedLevels(),
+        D->getPosition(), D->getIdentifier(), T, DI, ExpandedParameterPackTypes,
+        ExpandedParameterPackTypesAsWritten);
+  else
+    Param = NonTypeTemplateParmDecl::Create(
+        SemaRef.Context, Owner, D->getInnerLocStart(), D->getLocation(),
+        D->getDepth() - TemplateArgs.getNumSubstitutedLevels(),
+        D->getPosition(), D->getIdentifier(), T, D->isParameterPack(), DI);
+
+  Param->setAccess(AS_public);
+  if (Invalid)
+    Param->setInvalidDecl();
+
+  if (D->hasDefaultArgument() && !D->defaultArgumentWasInherited()) {
+    EnterExpressionEvaluationContext ConstantEvaluated(
+        SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+    ExprResult Value = SemaRef.SubstExpr(D->getDefaultArgument(), TemplateArgs);
+    if (!Value.isInvalid())
+      Param->setDefaultArgument(Value.get());
+  }
+
+  // Introduce this template parameter's instantiation into the instantiation
+  // scope.
+  SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Param);
+  return Param;
+}
+
+static void collectUnexpandedParameterPacks(
+    Sema &S,
+    TemplateParameterList *Params,
+    SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
+  for (const auto &P : *Params) {
+    if (P->isTemplateParameterPack())
+      continue;
+    if (NonTypeTemplateParmDecl *NTTP = dyn_cast<NonTypeTemplateParmDecl>(P))
+      S.collectUnexpandedParameterPacks(NTTP->getTypeSourceInfo()->getTypeLoc(),
+                                        Unexpanded);
+    if (TemplateTemplateParmDecl *TTP = dyn_cast<TemplateTemplateParmDecl>(P))
+      collectUnexpandedParameterPacks(S, TTP->getTemplateParameters(),
+                                      Unexpanded);
+  }
+}
+
+Decl *
+TemplateDeclInstantiator::VisitTemplateTemplateParmDecl(
+                                                  TemplateTemplateParmDecl *D) {
+  // Instantiate the template parameter list of the template template parameter.
+  TemplateParameterList *TempParams = D->getTemplateParameters();
+  TemplateParameterList *InstParams;
+  SmallVector<TemplateParameterList*, 8> ExpandedParams;
+
+  bool IsExpandedParameterPack = false;
+
+  if (D->isExpandedParameterPack()) {
+    // The template template parameter pack is an already-expanded pack
+    // expansion of template parameters. Substitute into each of the expanded
+    // parameters.
+    ExpandedParams.reserve(D->getNumExpansionTemplateParameters());
+    for (unsigned I = 0, N = D->getNumExpansionTemplateParameters();
+         I != N; ++I) {
+      LocalInstantiationScope Scope(SemaRef);
+      TemplateParameterList *Expansion =
+        SubstTemplateParams(D->getExpansionTemplateParameters(I));
+      if (!Expansion)
+        return nullptr;
+      ExpandedParams.push_back(Expansion);
+    }
+
+    IsExpandedParameterPack = true;
+    InstParams = TempParams;
+  } else if (D->isPackExpansion()) {
+    // The template template parameter pack expands to a pack of template
+    // template parameters. Determine whether we need to expand this parameter
+    // pack into separate parameters.
+    SmallVector<UnexpandedParameterPack, 2> Unexpanded;
+    collectUnexpandedParameterPacks(SemaRef, D->getTemplateParameters(),
+                                    Unexpanded);
+
+    // Determine whether the set of unexpanded parameter packs can and should
+    // be expanded.
+    bool Expand = true;
+    bool RetainExpansion = false;
+    Optional<unsigned> NumExpansions;
+    if (SemaRef.CheckParameterPacksForExpansion(D->getLocation(),
+                                                TempParams->getSourceRange(),
+                                                Unexpanded,
+                                                TemplateArgs,
+                                                Expand, RetainExpansion,
+                                                NumExpansions))
+      return nullptr;
+
+    if (Expand) {
+      for (unsigned I = 0; I != *NumExpansions; ++I) {
+        Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, I);
+        LocalInstantiationScope Scope(SemaRef);
+        TemplateParameterList *Expansion = SubstTemplateParams(TempParams);
+        if (!Expansion)
+          return nullptr;
+        ExpandedParams.push_back(Expansion);
+      }
+
+      // Note that we have an expanded parameter pack. The "type" of this
+      // expanded parameter pack is the original expansion type, but callers
+      // will end up using the expanded parameter pack types for type-checking.
+      IsExpandedParameterPack = true;
+      InstParams = TempParams;
+    } else {
+      // We cannot fully expand the pack expansion now, so just substitute
+      // into the pattern.
+      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, -1);
+
+      LocalInstantiationScope Scope(SemaRef);
+      InstParams = SubstTemplateParams(TempParams);
+      if (!InstParams)
+        return nullptr;
+    }
+  } else {
+    // Perform the actual substitution of template parameters within a new,
+    // local instantiation scope.
+    LocalInstantiationScope Scope(SemaRef);
+    InstParams = SubstTemplateParams(TempParams);
+    if (!InstParams)
+      return nullptr;
+  }
+
+  // Build the template template parameter.
+  TemplateTemplateParmDecl *Param;
+  if (IsExpandedParameterPack)
+    Param = TemplateTemplateParmDecl::Create(
+        SemaRef.Context, Owner, D->getLocation(),
+        D->getDepth() - TemplateArgs.getNumSubstitutedLevels(),
+        D->getPosition(), D->getIdentifier(), InstParams, ExpandedParams);
+  else
+    Param = TemplateTemplateParmDecl::Create(
+        SemaRef.Context, Owner, D->getLocation(),
+        D->getDepth() - TemplateArgs.getNumSubstitutedLevels(),
+        D->getPosition(), D->isParameterPack(), D->getIdentifier(), InstParams);
+  if (D->hasDefaultArgument() && !D->defaultArgumentWasInherited()) {
+    NestedNameSpecifierLoc QualifierLoc =
+        D->getDefaultArgument().getTemplateQualifierLoc();
+    QualifierLoc =
+        SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc, TemplateArgs);
+    TemplateName TName = SemaRef.SubstTemplateName(
+        QualifierLoc, D->getDefaultArgument().getArgument().getAsTemplate(),
+        D->getDefaultArgument().getTemplateNameLoc(), TemplateArgs);
+    if (!TName.isNull())
+      Param->setDefaultArgument(
+          SemaRef.Context,
+          TemplateArgumentLoc(TemplateArgument(TName),
+                              D->getDefaultArgument().getTemplateQualifierLoc(),
+                              D->getDefaultArgument().getTemplateNameLoc()));
+  }
+  Param->setAccess(AS_public);
+
+  // Introduce this template parameter's instantiation into the instantiation
+  // scope.
+  SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, Param);
+
+  return Param;
+}
+
+Decl *TemplateDeclInstantiator::VisitUsingDirectiveDecl(UsingDirectiveDecl *D) {
+  // Using directives are never dependent (and never contain any types or
+  // expressions), so they require no explicit instantiation work.
+
+  UsingDirectiveDecl *Inst
+    = UsingDirectiveDecl::Create(SemaRef.Context, Owner, D->getLocation(),
+                                 D->getNamespaceKeyLocation(),
+                                 D->getQualifierLoc(),
+                                 D->getIdentLocation(),
+                                 D->getNominatedNamespace(),
+                                 D->getCommonAncestor());
+
+  // Add the using directive to its declaration context
+  // only if this is not a function or method.
+  if (!Owner->isFunctionOrMethod())
+    Owner->addDecl(Inst);
+
+  return Inst;
+}
+
+Decl *TemplateDeclInstantiator::VisitUsingDecl(UsingDecl *D) {
+
+  // The nested name specifier may be dependent, for example
+  //     template <typename T> struct t {
+  //       struct s1 { T f1(); };
+  //       struct s2 : s1 { using s1::f1; };
+  //     };
+  //     template struct t<int>;
+  // Here, in using s1::f1, s1 refers to t<T>::s1;
+  // we need to substitute for t<int>::s1.
+  NestedNameSpecifierLoc QualifierLoc
+    = SemaRef.SubstNestedNameSpecifierLoc(D->getQualifierLoc(),
+                                          TemplateArgs);
+  if (!QualifierLoc)
+    return nullptr;
+
+  // For an inheriting constructor declaration, the name of the using
+  // declaration is the name of a constructor in this class, not in the
+  // base class.
+  DeclarationNameInfo NameInfo = D->getNameInfo();
+  if (NameInfo.getName().getNameKind() == DeclarationName::CXXConstructorName)
+    if (auto *RD = dyn_cast<CXXRecordDecl>(SemaRef.CurContext))
+      NameInfo.setName(SemaRef.Context.DeclarationNames.getCXXConstructorName(
+          SemaRef.Context.getCanonicalType(SemaRef.Context.getRecordType(RD))));
+
+  // We only need to do redeclaration lookups if we're in a class
+  // scope (in fact, it's not really even possible in non-class
+  // scopes).
+  bool CheckRedeclaration = Owner->isRecord();
+
+  LookupResult Prev(SemaRef, NameInfo, Sema::LookupUsingDeclName,
+                    Sema::ForVisibleRedeclaration);
+
+  UsingDecl *NewUD = UsingDecl::Create(SemaRef.Context, Owner,
+                                       D->getUsingLoc(),
+                                       QualifierLoc,
+                                       NameInfo,
+                                       D->hasTypename());
+
+  CXXScopeSpec SS;
+  SS.Adopt(QualifierLoc);
+  if (CheckRedeclaration) {
+    Prev.setHideTags(false);
+    SemaRef.LookupQualifiedName(Prev, Owner);
+
+    // Check for invalid redeclarations.
+    if (SemaRef.CheckUsingDeclRedeclaration(D->getUsingLoc(),
+                                            D->hasTypename(), SS,
+                                            D->getLocation(), Prev))
+      NewUD->setInvalidDecl();
+
+  }
+
+  if (!NewUD->isInvalidDecl() &&
+      SemaRef.CheckUsingDeclQualifier(D->getUsingLoc(), D->hasTypename(),
+                                      SS, NameInfo, D->getLocation()))
+    NewUD->setInvalidDecl();
+
+  SemaRef.Context.setInstantiatedFromUsingDecl(NewUD, D);
+  NewUD->setAccess(D->getAccess());
+  Owner->addDecl(NewUD);
+
+  // Don't process the shadow decls for an invalid decl.
+  if (NewUD->isInvalidDecl())
+    return NewUD;
+
+  if (NameInfo.getName().getNameKind() == DeclarationName::CXXConstructorName)
+    SemaRef.CheckInheritingConstructorUsingDecl(NewUD);
+
+  bool isFunctionScope = Owner->isFunctionOrMethod();
+
+  // Process the shadow decls.
+  for (auto *Shadow : D->shadows()) {
+    // FIXME: UsingShadowDecl doesn't preserve its immediate target, so
+    // reconstruct it in the case where it matters.
+    NamedDecl *OldTarget = Shadow->getTargetDecl();
+    if (auto *CUSD = dyn_cast<ConstructorUsingShadowDecl>(Shadow))
+      if (auto *BaseShadow = CUSD->getNominatedBaseClassShadowDecl())
+        OldTarget = BaseShadow;
+
+    NamedDecl *InstTarget =
+        cast_or_null<NamedDecl>(SemaRef.FindInstantiatedDecl(
+            Shadow->getLocation(), OldTarget, TemplateArgs));
+    if (!InstTarget)
+      return nullptr;
+
+    UsingShadowDecl *PrevDecl = nullptr;
+    if (CheckRedeclaration) {
+      if (SemaRef.CheckUsingShadowDecl(NewUD, InstTarget, Prev, PrevDecl))
+        continue;
+    } else if (UsingShadowDecl *OldPrev =
+                   getPreviousDeclForInstantiation(Shadow)) {
+      PrevDecl = cast_or_null<UsingShadowDecl>(SemaRef.FindInstantiatedDecl(
+          Shadow->getLocation(), OldPrev, TemplateArgs));
+    }
+
+    UsingShadowDecl *InstShadow =
+        SemaRef.BuildUsingShadowDecl(/*Scope*/nullptr, NewUD, InstTarget,
+                                     PrevDecl);
+    SemaRef.Context.setInstantiatedFromUsingShadowDecl(InstShadow, Shadow);
+
+    if (isFunctionScope)
+      SemaRef.CurrentInstantiationScope->InstantiatedLocal(Shadow, InstShadow);
+  }
+
+  return NewUD;
+}
+
+Decl *TemplateDeclInstantiator::VisitUsingShadowDecl(UsingShadowDecl *D) {
+  // Ignore these;  we handle them in bulk when processing the UsingDecl.
+  return nullptr;
+}
+
+Decl *TemplateDeclInstantiator::VisitConstructorUsingShadowDecl(
+    ConstructorUsingShadowDecl *D) {
+  // Ignore these;  we handle them in bulk when processing the UsingDecl.
+  return nullptr;
+}
+
+template <typename T>
+Decl *TemplateDeclInstantiator::instantiateUnresolvedUsingDecl(
+    T *D, bool InstantiatingPackElement) {
+  // If this is a pack expansion, expand it now.
+  if (D->isPackExpansion() && !InstantiatingPackElement) {
+    SmallVector<UnexpandedParameterPack, 2> Unexpanded;
+    SemaRef.collectUnexpandedParameterPacks(D->getQualifierLoc(), Unexpanded);
+    SemaRef.collectUnexpandedParameterPacks(D->getNameInfo(), Unexpanded);
+
+    // Determine whether the set of unexpanded parameter packs can and should
+    // be expanded.
+    bool Expand = true;
+    bool RetainExpansion = false;
+    Optional<unsigned> NumExpansions;
+    if (SemaRef.CheckParameterPacksForExpansion(
+          D->getEllipsisLoc(), D->getSourceRange(), Unexpanded, TemplateArgs,
+            Expand, RetainExpansion, NumExpansions))
+      return nullptr;
+
+    // This declaration cannot appear within a function template signature,
+    // so we can't have a partial argument list for a parameter pack.
+    assert(!RetainExpansion &&
+           "should never need to retain an expansion for UsingPackDecl");
+
+    if (!Expand) {
+      // We cannot fully expand the pack expansion now, so substitute into the
+      // pattern and create a new pack expansion.
+      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, -1);
+      return instantiateUnresolvedUsingDecl(D, true);
+    }
+
+    // Within a function, we don't have any normal way to check for conflicts
+    // between shadow declarations from different using declarations in the
+    // same pack expansion, but this is always ill-formed because all expansions
+    // must produce (conflicting) enumerators.
+    //
+    // Sadly we can't just reject this in the template definition because it
+    // could be valid if the pack is empty or has exactly one expansion.
+    if (D->getDeclContext()->isFunctionOrMethod() && *NumExpansions > 1) {
+      SemaRef.Diag(D->getEllipsisLoc(),
+                   diag::err_using_decl_redeclaration_expansion);
+      return nullptr;
+    }
+
+    // Instantiate the slices of this pack and build a UsingPackDecl.
+    SmallVector<NamedDecl*, 8> Expansions;
+    for (unsigned I = 0; I != *NumExpansions; ++I) {
+      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, I);
+      Decl *Slice = instantiateUnresolvedUsingDecl(D, true);
+      if (!Slice)
+        return nullptr;
+      // Note that we can still get unresolved using declarations here, if we
+      // had arguments for all packs but the pattern also contained other
+      // template arguments (this only happens during partial substitution, eg
+      // into the body of a generic lambda in a function template).
+      Expansions.push_back(cast<NamedDecl>(Slice));
+    }
+
+    auto *NewD = SemaRef.BuildUsingPackDecl(D, Expansions);
+    if (isDeclWithinFunction(D))
+      SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewD);
+    return NewD;
+  }
+
+  UnresolvedUsingTypenameDecl *TD = dyn_cast<UnresolvedUsingTypenameDecl>(D);
+  SourceLocation TypenameLoc = TD ? TD->getTypenameLoc() : SourceLocation();
+
+  NestedNameSpecifierLoc QualifierLoc
+    = SemaRef.SubstNestedNameSpecifierLoc(D->getQualifierLoc(),
+                                          TemplateArgs);
+  if (!QualifierLoc)
+    return nullptr;
+
+  CXXScopeSpec SS;
+  SS.Adopt(QualifierLoc);
+
+  DeclarationNameInfo NameInfo
+    = SemaRef.SubstDeclarationNameInfo(D->getNameInfo(), TemplateArgs);
+
+  // Produce a pack expansion only if we're not instantiating a particular
+  // slice of a pack expansion.
+  bool InstantiatingSlice = D->getEllipsisLoc().isValid() &&
+                            SemaRef.ArgumentPackSubstitutionIndex != -1;
+  SourceLocation EllipsisLoc =
+      InstantiatingSlice ? SourceLocation() : D->getEllipsisLoc();
+
+  NamedDecl *UD = SemaRef.BuildUsingDeclaration(
+      /*Scope*/ nullptr, D->getAccess(), D->getUsingLoc(),
+      /*HasTypename*/ TD, TypenameLoc, SS, NameInfo, EllipsisLoc,
+      ParsedAttributesView(),
+      /*IsInstantiation*/ true);
+  if (UD)
+    SemaRef.Context.setInstantiatedFromUsingDecl(UD, D);
+
+  return UD;
+}
+
+Decl *TemplateDeclInstantiator::VisitUnresolvedUsingTypenameDecl(
+    UnresolvedUsingTypenameDecl *D) {
+  return instantiateUnresolvedUsingDecl(D);
+}
+
+Decl *TemplateDeclInstantiator::VisitUnresolvedUsingValueDecl(
+    UnresolvedUsingValueDecl *D) {
+  return instantiateUnresolvedUsingDecl(D);
+}
+
+Decl *TemplateDeclInstantiator::VisitUsingPackDecl(UsingPackDecl *D) {
+  SmallVector<NamedDecl*, 8> Expansions;
+  for (auto *UD : D->expansions()) {
+    if (NamedDecl *NewUD =
+            SemaRef.FindInstantiatedDecl(D->getLocation(), UD, TemplateArgs))
+      Expansions.push_back(NewUD);
+    else
+      return nullptr;
+  }
+
+  auto *NewD = SemaRef.BuildUsingPackDecl(D, Expansions);
+  if (isDeclWithinFunction(D))
+    SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewD);
+  return NewD;
+}
+
+Decl *TemplateDeclInstantiator::VisitClassScopeFunctionSpecializationDecl(
+    ClassScopeFunctionSpecializationDecl *Decl) {
+  CXXMethodDecl *OldFD = Decl->getSpecialization();
+  return cast_or_null<CXXMethodDecl>(
+      VisitCXXMethodDecl(OldFD, nullptr, Decl->getTemplateArgsAsWritten()));
+}
+
+Decl *TemplateDeclInstantiator::VisitOMPThreadPrivateDecl(
+                                     OMPThreadPrivateDecl *D) {
+  SmallVector<Expr *, 5> Vars;
+  for (auto *I : D->varlists()) {
+    Expr *Var = SemaRef.SubstExpr(I, TemplateArgs).get();
+    assert(isa<DeclRefExpr>(Var) && "threadprivate arg is not a DeclRefExpr");
+    Vars.push_back(Var);
+  }
+
+  OMPThreadPrivateDecl *TD =
+    SemaRef.CheckOMPThreadPrivateDecl(D->getLocation(), Vars);
+
+  TD->setAccess(AS_public);
+  Owner->addDecl(TD);
+
+  return TD;
+}
+
+Decl *TemplateDeclInstantiator::VisitOMPAllocateDecl(OMPAllocateDecl *D) {
+  SmallVector<Expr *, 5> Vars;
+  for (auto *I : D->varlists()) {
+    Expr *Var = SemaRef.SubstExpr(I, TemplateArgs).get();
+    assert(isa<DeclRefExpr>(Var) && "allocate arg is not a DeclRefExpr");
+    Vars.push_back(Var);
+  }
+  SmallVector<OMPClause *, 4> Clauses;
+  // Copy map clauses from the original mapper.
+  for (OMPClause *C : D->clauselists()) {
+    auto *AC = cast<OMPAllocatorClause>(C);
+    ExprResult NewE = SemaRef.SubstExpr(AC->getAllocator(), TemplateArgs);
+    if (!NewE.isUsable())
+      continue;
+    OMPClause *IC = SemaRef.ActOnOpenMPAllocatorClause(
+        NewE.get(), AC->getBeginLoc(), AC->getLParenLoc(), AC->getEndLoc());
+    Clauses.push_back(IC);
+  }
+
+  Sema::DeclGroupPtrTy Res = SemaRef.ActOnOpenMPAllocateDirective(
+      D->getLocation(), Vars, Clauses, Owner);
+  if (Res.get().isNull())
+    return nullptr;
+  return Res.get().getSingleDecl();
+}
+
+Decl *TemplateDeclInstantiator::VisitOMPRequiresDecl(OMPRequiresDecl *D) {
+  llvm_unreachable(
+      "Requires directive cannot be instantiated within a dependent context");
+}
+
+Decl *TemplateDeclInstantiator::VisitOMPDeclareReductionDecl(
+    OMPDeclareReductionDecl *D) {
+  // Instantiate type and check if it is allowed.
+  const bool RequiresInstantiation =
+      D->getType()->isDependentType() ||
+      D->getType()->isInstantiationDependentType() ||
+      D->getType()->containsUnexpandedParameterPack();
+  QualType SubstReductionType;
+  if (RequiresInstantiation) {
+    SubstReductionType = SemaRef.ActOnOpenMPDeclareReductionType(
+        D->getLocation(),
+        ParsedType::make(SemaRef.SubstType(
+            D->getType(), TemplateArgs, D->getLocation(), DeclarationName())));
+  } else {
+    SubstReductionType = D->getType();
+  }
+  if (SubstReductionType.isNull())
+    return nullptr;
+  bool IsCorrect = !SubstReductionType.isNull();
+  // Create instantiated copy.
+  std::pair<QualType, SourceLocation> ReductionTypes[] = {
+      std::make_pair(SubstReductionType, D->getLocation())};
+  auto *PrevDeclInScope = D->getPrevDeclInScope();
+  if (PrevDeclInScope && !PrevDeclInScope->isInvalidDecl()) {
+    PrevDeclInScope = cast<OMPDeclareReductionDecl>(
+        SemaRef.CurrentInstantiationScope->findInstantiationOf(PrevDeclInScope)
+            ->get<Decl *>());
+  }
+  auto DRD = SemaRef.ActOnOpenMPDeclareReductionDirectiveStart(
+      /*S=*/nullptr, Owner, D->getDeclName(), ReductionTypes, D->getAccess(),
+      PrevDeclInScope);
+  auto *NewDRD = cast<OMPDeclareReductionDecl>(DRD.get().getSingleDecl());
+  SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewDRD);
+  if (!RequiresInstantiation) {
+    if (Expr *Combiner = D->getCombiner()) {
+      NewDRD->setCombinerData(D->getCombinerIn(), D->getCombinerOut());
+      NewDRD->setCombiner(Combiner);
+      if (Expr *Init = D->getInitializer()) {
+        NewDRD->setInitializerData(D->getInitOrig(), D->getInitPriv());
+        NewDRD->setInitializer(Init, D->getInitializerKind());
+      }
+    }
+    (void)SemaRef.ActOnOpenMPDeclareReductionDirectiveEnd(
+        /*S=*/nullptr, DRD, IsCorrect && !D->isInvalidDecl());
+    return NewDRD;
+  }
+  Expr *SubstCombiner = nullptr;
+  Expr *SubstInitializer = nullptr;
+  // Combiners instantiation sequence.
+  if (D->getCombiner()) {
+    SemaRef.ActOnOpenMPDeclareReductionCombinerStart(
+        /*S=*/nullptr, NewDRD);
+    SemaRef.CurrentInstantiationScope->InstantiatedLocal(
+        cast<DeclRefExpr>(D->getCombinerIn())->getDecl(),
+        cast<DeclRefExpr>(NewDRD->getCombinerIn())->getDecl());
+    SemaRef.CurrentInstantiationScope->InstantiatedLocal(
+        cast<DeclRefExpr>(D->getCombinerOut())->getDecl(),
+        cast<DeclRefExpr>(NewDRD->getCombinerOut())->getDecl());
+    auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(Owner);
+    Sema::CXXThisScopeRAII ThisScope(SemaRef, ThisContext, Qualifiers(),
+                                     ThisContext);
+    SubstCombiner = SemaRef.SubstExpr(D->getCombiner(), TemplateArgs).get();
+    SemaRef.ActOnOpenMPDeclareReductionCombinerEnd(NewDRD, SubstCombiner);
+    // Initializers instantiation sequence.
+    if (D->getInitializer()) {
+      VarDecl *OmpPrivParm =
+          SemaRef.ActOnOpenMPDeclareReductionInitializerStart(
+              /*S=*/nullptr, NewDRD);
+      SemaRef.CurrentInstantiationScope->InstantiatedLocal(
+          cast<DeclRefExpr>(D->getInitOrig())->getDecl(),
+          cast<DeclRefExpr>(NewDRD->getInitOrig())->getDecl());
+      SemaRef.CurrentInstantiationScope->InstantiatedLocal(
+          cast<DeclRefExpr>(D->getInitPriv())->getDecl(),
+          cast<DeclRefExpr>(NewDRD->getInitPriv())->getDecl());
+      if (D->getInitializerKind() == OMPDeclareReductionDecl::CallInit) {
+        SubstInitializer =
+            SemaRef.SubstExpr(D->getInitializer(), TemplateArgs).get();
+      } else {
+        IsCorrect = IsCorrect && OmpPrivParm->hasInit();
+      }
+      SemaRef.ActOnOpenMPDeclareReductionInitializerEnd(
+          NewDRD, SubstInitializer, OmpPrivParm);
+    }
+    IsCorrect =
+        IsCorrect && SubstCombiner &&
+        (!D->getInitializer() ||
+         (D->getInitializerKind() == OMPDeclareReductionDecl::CallInit &&
+          SubstInitializer) ||
+         (D->getInitializerKind() != OMPDeclareReductionDecl::CallInit &&
+          !SubstInitializer && !SubstInitializer));
+  } else {
+    IsCorrect = false;
+  }
+
+  (void)SemaRef.ActOnOpenMPDeclareReductionDirectiveEnd(/*S=*/nullptr, DRD,
+                                                        IsCorrect);
+
+  return NewDRD;
+}
+
+Decl *
+TemplateDeclInstantiator::VisitOMPDeclareMapperDecl(OMPDeclareMapperDecl *D) {
+  // Instantiate type and check if it is allowed.
+  const bool RequiresInstantiation =
+      D->getType()->isDependentType() ||
+      D->getType()->isInstantiationDependentType() ||
+      D->getType()->containsUnexpandedParameterPack();
+  QualType SubstMapperTy;
+  DeclarationName VN = D->getVarName();
+  if (RequiresInstantiation) {
+    SubstMapperTy = SemaRef.ActOnOpenMPDeclareMapperType(
+        D->getLocation(),
+        ParsedType::make(SemaRef.SubstType(D->getType(), TemplateArgs,
+                                           D->getLocation(), VN)));
+  } else {
+    SubstMapperTy = D->getType();
+  }
+  if (SubstMapperTy.isNull())
+    return nullptr;
+  // Create an instantiated copy of mapper.
+  auto *PrevDeclInScope = D->getPrevDeclInScope();
+  if (PrevDeclInScope && !PrevDeclInScope->isInvalidDecl()) {
+    PrevDeclInScope = cast<OMPDeclareMapperDecl>(
+        SemaRef.CurrentInstantiationScope->findInstantiationOf(PrevDeclInScope)
+            ->get<Decl *>());
+  }
+  OMPDeclareMapperDecl *NewDMD = SemaRef.ActOnOpenMPDeclareMapperDirectiveStart(
+      /*S=*/nullptr, Owner, D->getDeclName(), SubstMapperTy, D->getLocation(),
+      VN, D->getAccess(), PrevDeclInScope);
+  SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewDMD);
+  SmallVector<OMPClause *, 6> Clauses;
+  bool IsCorrect = true;
+  if (!RequiresInstantiation) {
+    // Copy the mapper variable.
+    NewDMD->setMapperVarRef(D->getMapperVarRef());
+    // Copy map clauses from the original mapper.
+    for (OMPClause *C : D->clauselists())
+      Clauses.push_back(C);
+  } else {
+    // Instantiate the mapper variable.
+    DeclarationNameInfo DirName;
+    SemaRef.StartOpenMPDSABlock(OMPD_declare_mapper, DirName, /*S=*/nullptr,
+                                (*D->clauselist_begin())->getBeginLoc());
+    SemaRef.ActOnOpenMPDeclareMapperDirectiveVarDecl(
+        NewDMD, /*S=*/nullptr, SubstMapperTy, D->getLocation(), VN);
+    SemaRef.CurrentInstantiationScope->InstantiatedLocal(
+        cast<DeclRefExpr>(D->getMapperVarRef())->getDecl(),
+        cast<DeclRefExpr>(NewDMD->getMapperVarRef())->getDecl());
+    auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(Owner);
+    Sema::CXXThisScopeRAII ThisScope(SemaRef, ThisContext, Qualifiers(),
+                                     ThisContext);
+    // Instantiate map clauses.
+    for (OMPClause *C : D->clauselists()) {
+      auto *OldC = cast<OMPMapClause>(C);
+      SmallVector<Expr *, 4> NewVars;
+      for (Expr *OE : OldC->varlists()) {
+        Expr *NE = SemaRef.SubstExpr(OE, TemplateArgs).get();
+        if (!NE) {
+          IsCorrect = false;
+          break;
+        }
+        NewVars.push_back(NE);
+      }
+      if (!IsCorrect)
+        break;
+      NestedNameSpecifierLoc NewQualifierLoc =
+          SemaRef.SubstNestedNameSpecifierLoc(OldC->getMapperQualifierLoc(),
+                                              TemplateArgs);
+      CXXScopeSpec SS;
+      SS.Adopt(NewQualifierLoc);
+      DeclarationNameInfo NewNameInfo = SemaRef.SubstDeclarationNameInfo(
+          OldC->getMapperIdInfo(), TemplateArgs);
+      OMPVarListLocTy Locs(OldC->getBeginLoc(), OldC->getLParenLoc(),
+                           OldC->getEndLoc());
+      OMPClause *NewC = SemaRef.ActOnOpenMPMapClause(
+          OldC->getMapTypeModifiers(), OldC->getMapTypeModifiersLoc(), SS,
+          NewNameInfo, OldC->getMapType(), OldC->isImplicitMapType(),
+          OldC->getMapLoc(), OldC->getColonLoc(), NewVars, Locs);
+      Clauses.push_back(NewC);
+    }
+    SemaRef.EndOpenMPDSABlock(nullptr);
+  }
+  (void)SemaRef.ActOnOpenMPDeclareMapperDirectiveEnd(NewDMD, /*S=*/nullptr,
+                                                     Clauses);
+  if (!IsCorrect)
+    return nullptr;
+  return NewDMD;
+}
+
+Decl *TemplateDeclInstantiator::VisitOMPCapturedExprDecl(
+    OMPCapturedExprDecl * /*D*/) {
+  llvm_unreachable("Should not be met in templates");
+}
+
+Decl *TemplateDeclInstantiator::VisitFunctionDecl(FunctionDecl *D) {
+  return VisitFunctionDecl(D, nullptr);
+}
+
+Decl *
+TemplateDeclInstantiator::VisitCXXDeductionGuideDecl(CXXDeductionGuideDecl *D) {
+  Decl *Inst = VisitFunctionDecl(D, nullptr);
+  if (Inst && !D->getDescribedFunctionTemplate())
+    Owner->addDecl(Inst);
+  return Inst;
+}
+
+Decl *TemplateDeclInstantiator::VisitCXXMethodDecl(CXXMethodDecl *D) {
+  return VisitCXXMethodDecl(D, nullptr);
+}
+
+Decl *TemplateDeclInstantiator::VisitRecordDecl(RecordDecl *D) {
+  llvm_unreachable("There are only CXXRecordDecls in C++");
+}
+
+Decl *
+TemplateDeclInstantiator::VisitClassTemplateSpecializationDecl(
+    ClassTemplateSpecializationDecl *D) {
+  // As a MS extension, we permit class-scope explicit specialization
+  // of member class templates.
+  ClassTemplateDecl *ClassTemplate = D->getSpecializedTemplate();
+  assert(ClassTemplate->getDeclContext()->isRecord() &&
+         D->getTemplateSpecializationKind() == TSK_ExplicitSpecialization &&
+         "can only instantiate an explicit specialization "
+         "for a member class template");
+
+  // Lookup the already-instantiated declaration in the instantiation
+  // of the class template.
+  ClassTemplateDecl *InstClassTemplate =
+      cast_or_null<ClassTemplateDecl>(SemaRef.FindInstantiatedDecl(
+          D->getLocation(), ClassTemplate, TemplateArgs));
+  if (!InstClassTemplate)
+    return nullptr;
+
+  // Substitute into the template arguments of the class template explicit
+  // specialization.
+  TemplateSpecializationTypeLoc Loc = D->getTypeAsWritten()->getTypeLoc().
+                                        castAs<TemplateSpecializationTypeLoc>();
+  TemplateArgumentListInfo InstTemplateArgs(Loc.getLAngleLoc(),
+                                            Loc.getRAngleLoc());
+  SmallVector<TemplateArgumentLoc, 4> ArgLocs;
+  for (unsigned I = 0; I != Loc.getNumArgs(); ++I)
+    ArgLocs.push_back(Loc.getArgLoc(I));
+  if (SemaRef.Subst(ArgLocs.data(), ArgLocs.size(),
+                    InstTemplateArgs, TemplateArgs))
+    return nullptr;
+
+  // Check that the template argument list is well-formed for this
+  // class template.
+  SmallVector<TemplateArgument, 4> Converted;
+  if (SemaRef.CheckTemplateArgumentList(InstClassTemplate,
+                                        D->getLocation(),
+                                        InstTemplateArgs,
+                                        false,
+                                        Converted))
+    return nullptr;
+
+  // Figure out where to insert this class template explicit specialization
+  // in the member template's set of class template explicit specializations.
+  void *InsertPos = nullptr;
+  ClassTemplateSpecializationDecl *PrevDecl =
+      InstClassTemplate->findSpecialization(Converted, InsertPos);
+
+  // Check whether we've already seen a conflicting instantiation of this
+  // declaration (for instance, if there was a prior implicit instantiation).
+  bool Ignored;
+  if (PrevDecl &&
+      SemaRef.CheckSpecializationInstantiationRedecl(D->getLocation(),
+                                                     D->getSpecializationKind(),
+                                                     PrevDecl,
+                                                     PrevDecl->getSpecializationKind(),
+                                                     PrevDecl->getPointOfInstantiation(),
+                                                     Ignored))
+    return nullptr;
+
+  // If PrevDecl was a definition and D is also a definition, diagnose.
+  // This happens in cases like:
+  //
+  //   template<typename T, typename U>
+  //   struct Outer {
+  //     template<typename X> struct Inner;
+  //     template<> struct Inner<T> {};
+  //     template<> struct Inner<U> {};
+  //   };
+  //
+  //   Outer<int, int> outer; // error: the explicit specializations of Inner
+  //                          // have the same signature.
+  if (PrevDecl && PrevDecl->getDefinition() &&
+      D->isThisDeclarationADefinition()) {
+    SemaRef.Diag(D->getLocation(), diag::err_redefinition) << PrevDecl;
+    SemaRef.Diag(PrevDecl->getDefinition()->getLocation(),
+                 diag::note_previous_definition);
+    return nullptr;
+  }
+
+  // Create the class template partial specialization declaration.
+  ClassTemplateSpecializationDecl *InstD =
+      ClassTemplateSpecializationDecl::Create(
+          SemaRef.Context, D->getTagKind(), Owner, D->getBeginLoc(),
+          D->getLocation(), InstClassTemplate, Converted, PrevDecl);
+
+  // Add this partial specialization to the set of class template partial
+  // specializations.
+  if (!PrevDecl)
+    InstClassTemplate->AddSpecialization(InstD, InsertPos);
+
+  // Substitute the nested name specifier, if any.
+  if (SubstQualifier(D, InstD))
+    return nullptr;
+
+  // Build the canonical type that describes the converted template
+  // arguments of the class template explicit specialization.
+  QualType CanonType = SemaRef.Context.getTemplateSpecializationType(
+      TemplateName(InstClassTemplate), Converted,
+      SemaRef.Context.getRecordType(InstD));
+
+  // Build the fully-sugared type for this class template
+  // specialization as the user wrote in the specialization
+  // itself. This means that we'll pretty-print the type retrieved
+  // from the specialization's declaration the way that the user
+  // actually wrote the specialization, rather than formatting the
+  // name based on the "canonical" representation used to store the
+  // template arguments in the specialization.
+  TypeSourceInfo *WrittenTy = SemaRef.Context.getTemplateSpecializationTypeInfo(
+      TemplateName(InstClassTemplate), D->getLocation(), InstTemplateArgs,
+      CanonType);
+
+  InstD->setAccess(D->getAccess());
+  InstD->setInstantiationOfMemberClass(D, TSK_ImplicitInstantiation);
+  InstD->setSpecializationKind(D->getSpecializationKind());
+  InstD->setTypeAsWritten(WrittenTy);
+  InstD->setExternLoc(D->getExternLoc());
+  InstD->setTemplateKeywordLoc(D->getTemplateKeywordLoc());
+
+  Owner->addDecl(InstD);
+
+  // Instantiate the members of the class-scope explicit specialization eagerly.
+  // We don't have support for lazy instantiation of an explicit specialization
+  // yet, and MSVC eagerly instantiates in this case.
+  // FIXME: This is wrong in standard C++.
+  if (D->isThisDeclarationADefinition() &&
+      SemaRef.InstantiateClass(D->getLocation(), InstD, D, TemplateArgs,
+                               TSK_ImplicitInstantiation,
+                               /*Complain=*/true))
+    return nullptr;
+
+  return InstD;
+}
+
+Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
+    VarTemplateSpecializationDecl *D) {
+
+  TemplateArgumentListInfo VarTemplateArgsInfo;
+  VarTemplateDecl *VarTemplate = D->getSpecializedTemplate();
+  assert(VarTemplate &&
+         "A template specialization without specialized template?");
+
+  VarTemplateDecl *InstVarTemplate =
+      cast_or_null<VarTemplateDecl>(SemaRef.FindInstantiatedDecl(
+          D->getLocation(), VarTemplate, TemplateArgs));
+  if (!InstVarTemplate)
+    return nullptr;
+
+  // Substitute the current template arguments.
+  const TemplateArgumentListInfo &TemplateArgsInfo = D->getTemplateArgsInfo();
+  VarTemplateArgsInfo.setLAngleLoc(TemplateArgsInfo.getLAngleLoc());
+  VarTemplateArgsInfo.setRAngleLoc(TemplateArgsInfo.getRAngleLoc());
+
+  if (SemaRef.Subst(TemplateArgsInfo.getArgumentArray(),
+                    TemplateArgsInfo.size(), VarTemplateArgsInfo, TemplateArgs))
+    return nullptr;
+
+  // Check that the template argument list is well-formed for this template.
+  SmallVector<TemplateArgument, 4> Converted;
+  if (SemaRef.CheckTemplateArgumentList(InstVarTemplate, D->getLocation(),
+                                        VarTemplateArgsInfo, false, Converted))
+    return nullptr;
+
+  // Check whether we've already seen a declaration of this specialization.
+  void *InsertPos = nullptr;
+  VarTemplateSpecializationDecl *PrevDecl =
+      InstVarTemplate->findSpecialization(Converted, InsertPos);
+
+  // Check whether we've already seen a conflicting instantiation of this
+  // declaration (for instance, if there was a prior implicit instantiation).
+  bool Ignored;
+  if (PrevDecl && SemaRef.CheckSpecializationInstantiationRedecl(
+                      D->getLocation(), D->getSpecializationKind(), PrevDecl,
+                      PrevDecl->getSpecializationKind(),
+                      PrevDecl->getPointOfInstantiation(), Ignored))
+    return nullptr;
+
+  return VisitVarTemplateSpecializationDecl(
+      InstVarTemplate, D, InsertPos, VarTemplateArgsInfo, Converted, PrevDecl);
+}
+
+Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
+    VarTemplateDecl *VarTemplate, VarDecl *D, void *InsertPos,
+    const TemplateArgumentListInfo &TemplateArgsInfo,
+    ArrayRef<TemplateArgument> Converted,
+    VarTemplateSpecializationDecl *PrevDecl) {
+
+  // Do substitution on the type of the declaration
+  TypeSourceInfo *DI =
+      SemaRef.SubstType(D->getTypeSourceInfo(), TemplateArgs,
+                        D->getTypeSpecStartLoc(), D->getDeclName());
+  if (!DI)
+    return nullptr;
+
+  if (DI->getType()->isFunctionType()) {
+    SemaRef.Diag(D->getLocation(), diag::err_variable_instantiates_to_function)
+        << D->isStaticDataMember() << DI->getType();
+    return nullptr;
+  }
+
+  // Build the instantiated declaration
+  VarTemplateSpecializationDecl *Var = VarTemplateSpecializationDecl::Create(
+      SemaRef.Context, Owner, D->getInnerLocStart(), D->getLocation(),
+      VarTemplate, DI->getType(), DI, D->getStorageClass(), Converted);
+  Var->setTemplateArgsInfo(TemplateArgsInfo);
+  if (InsertPos)
+    VarTemplate->AddSpecialization(Var, InsertPos);
+
+  // Substitute the nested name specifier, if any.
+  if (SubstQualifier(D, Var))
+    return nullptr;
+
+  SemaRef.BuildVariableInstantiation(Var, D, TemplateArgs, LateAttrs, Owner,
+                                     StartingScope, false, PrevDecl);
+
+  return Var;
+}
+
+Decl *TemplateDeclInstantiator::VisitObjCAtDefsFieldDecl(ObjCAtDefsFieldDecl *D) {
+  llvm_unreachable("@defs is not supported in Objective-C++");
+}
+
+Decl *TemplateDeclInstantiator::VisitFriendTemplateDecl(FriendTemplateDecl *D) {
+  // FIXME: We need to be able to instantiate FriendTemplateDecls.
+  unsigned DiagID = SemaRef.getDiagnostics().getCustomDiagID(
+                                               DiagnosticsEngine::Error,
+                                               "cannot instantiate %0 yet");
+  SemaRef.Diag(D->getLocation(), DiagID)
+    << D->getDeclKindName();
+
+  return nullptr;
+}
+
+Decl *TemplateDeclInstantiator::VisitConceptDecl(ConceptDecl *D) {
+  llvm_unreachable("Concept definitions cannot reside inside a template");
+}
+
+Decl *TemplateDeclInstantiator::VisitDecl(Decl *D) {
+  llvm_unreachable("Unexpected decl");
+}
+
+Decl *Sema::SubstDecl(Decl *D, DeclContext *Owner,
+                      const MultiLevelTemplateArgumentList &TemplateArgs) {
+  TemplateDeclInstantiator Instantiator(*this, Owner, TemplateArgs);
+  if (D->isInvalidDecl())
+    return nullptr;
+
+  return Instantiator.Visit(D);
+}
+
+/// Instantiates a nested template parameter list in the current
+/// instantiation context.
+///
+/// \param L The parameter list to instantiate
+///
+/// \returns NULL if there was an error
+TemplateParameterList *
+TemplateDeclInstantiator::SubstTemplateParams(TemplateParameterList *L) {
+  // Get errors for all the parameters before bailing out.
+  bool Invalid = false;
+
+  unsigned N = L->size();
+  typedef SmallVector<NamedDecl *, 8> ParamVector;
+  ParamVector Params;
+  Params.reserve(N);
+  for (auto &P : *L) {
+    NamedDecl *D = cast_or_null<NamedDecl>(Visit(P));
+    Params.push_back(D);
+    Invalid = Invalid || !D || D->isInvalidDecl();
+  }
+
+  // Clean up if we had an error.
+  if (Invalid)
+    return nullptr;
+
+  // Note: we substitute into associated constraints later
+  Expr *const UninstantiatedRequiresClause = L->getRequiresClause();
+
+  TemplateParameterList *InstL
+    = TemplateParameterList::Create(SemaRef.Context, L->getTemplateLoc(),
+                                    L->getLAngleLoc(), Params,
+                                    L->getRAngleLoc(),
+                                    UninstantiatedRequiresClause);
+  return InstL;
+}
+
+TemplateParameterList *
+Sema::SubstTemplateParams(TemplateParameterList *Params, DeclContext *Owner,
+                          const MultiLevelTemplateArgumentList &TemplateArgs) {
+  TemplateDeclInstantiator Instantiator(*this, Owner, TemplateArgs);
+  return Instantiator.SubstTemplateParams(Params);
+}
+
+/// Instantiate the declaration of a class template partial
+/// specialization.
+///
+/// \param ClassTemplate the (instantiated) class template that is partially
+// specialized by the instantiation of \p PartialSpec.
+///
+/// \param PartialSpec the (uninstantiated) class template partial
+/// specialization that we are instantiating.
+///
+/// \returns The instantiated partial specialization, if successful; otherwise,
+/// NULL to indicate an error.
+ClassTemplatePartialSpecializationDecl *
+TemplateDeclInstantiator::InstantiateClassTemplatePartialSpecialization(
+                                            ClassTemplateDecl *ClassTemplate,
+                          ClassTemplatePartialSpecializationDecl *PartialSpec) {
+  // Create a local instantiation scope for this class template partial
+  // specialization, which will contain the instantiations of the template
+  // parameters.
+  LocalInstantiationScope Scope(SemaRef);
+
+  // Substitute into the template parameters of the class template partial
+  // specialization.
+  TemplateParameterList *TempParams = PartialSpec->getTemplateParameters();
+  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
+  if (!InstParams)
+    return nullptr;
+
+  // Substitute into the template arguments of the class template partial
+  // specialization.
+  const ASTTemplateArgumentListInfo *TemplArgInfo
+    = PartialSpec->getTemplateArgsAsWritten();
+  TemplateArgumentListInfo InstTemplateArgs(TemplArgInfo->LAngleLoc,
+                                            TemplArgInfo->RAngleLoc);
+  if (SemaRef.Subst(TemplArgInfo->getTemplateArgs(),
+                    TemplArgInfo->NumTemplateArgs,
+                    InstTemplateArgs, TemplateArgs))
+    return nullptr;
+
+  // Check that the template argument list is well-formed for this
+  // class template.
+  SmallVector<TemplateArgument, 4> Converted;
+  if (SemaRef.CheckTemplateArgumentList(ClassTemplate,
+                                        PartialSpec->getLocation(),
+                                        InstTemplateArgs,
+                                        false,
+                                        Converted))
+    return nullptr;
+
+  // Check these arguments are valid for a template partial specialization.
+  if (SemaRef.CheckTemplatePartialSpecializationArgs(
+          PartialSpec->getLocation(), ClassTemplate, InstTemplateArgs.size(),
+          Converted))
+    return nullptr;
+
+  // Figure out where to insert this class template partial specialization
+  // in the member template's set of class template partial specializations.
+  void *InsertPos = nullptr;
+  ClassTemplateSpecializationDecl *PrevDecl
+    = ClassTemplate->findPartialSpecialization(Converted, InsertPos);
+
+  // Build the canonical type that describes the converted template
+  // arguments of the class template partial specialization.
+  QualType CanonType
+    = SemaRef.Context.getTemplateSpecializationType(TemplateName(ClassTemplate),
+                                                    Converted);
+
+  // Build the fully-sugared type for this class template
+  // specialization as the user wrote in the specialization
+  // itself. This means that we'll pretty-print the type retrieved
+  // from the specialization's declaration the way that the user
+  // actually wrote the specialization, rather than formatting the
+  // name based on the "canonical" representation used to store the
+  // template arguments in the specialization.
+  TypeSourceInfo *WrittenTy
+    = SemaRef.Context.getTemplateSpecializationTypeInfo(
+                                                    TemplateName(ClassTemplate),
+                                                    PartialSpec->getLocation(),
+                                                    InstTemplateArgs,
+                                                    CanonType);
+
+  if (PrevDecl) {
+    // We've already seen a partial specialization with the same template
+    // parameters and template arguments. This can happen, for example, when
+    // substituting the outer template arguments ends up causing two
+    // class template partial specializations of a member class template
+    // to have identical forms, e.g.,
+    //
+    //   template<typename T, typename U>
+    //   struct Outer {
+    //     template<typename X, typename Y> struct Inner;
+    //     template<typename Y> struct Inner<T, Y>;
+    //     template<typename Y> struct Inner<U, Y>;
+    //   };
+    //
+    //   Outer<int, int> outer; // error: the partial specializations of Inner
+    //                          // have the same signature.
+    SemaRef.Diag(PartialSpec->getLocation(), diag::err_partial_spec_redeclared)
+      << WrittenTy->getType();
+    SemaRef.Diag(PrevDecl->getLocation(), diag::note_prev_partial_spec_here)
+      << SemaRef.Context.getTypeDeclType(PrevDecl);
+    return nullptr;
+  }
+
+
+  // Create the class template partial specialization declaration.
+  ClassTemplatePartialSpecializationDecl *InstPartialSpec =
+      ClassTemplatePartialSpecializationDecl::Create(
+          SemaRef.Context, PartialSpec->getTagKind(), Owner,
+          PartialSpec->getBeginLoc(), PartialSpec->getLocation(), InstParams,
+          ClassTemplate, Converted, InstTemplateArgs, CanonType, nullptr);
+  // Substitute the nested name specifier, if any.
+  if (SubstQualifier(PartialSpec, InstPartialSpec))
+    return nullptr;
+
+  InstPartialSpec->setInstantiatedFromMember(PartialSpec);
+  InstPartialSpec->setTypeAsWritten(WrittenTy);
+
+  // Check the completed partial specialization.
+  SemaRef.CheckTemplatePartialSpecialization(InstPartialSpec);
+
+  // Add this partial specialization to the set of class template partial
+  // specializations.
+  ClassTemplate->AddPartialSpecialization(InstPartialSpec,
+                                          /*InsertPos=*/nullptr);
+  return InstPartialSpec;
+}
+
+/// Instantiate the declaration of a variable template partial
+/// specialization.
+///
+/// \param VarTemplate the (instantiated) variable template that is partially
+/// specialized by the instantiation of \p PartialSpec.
+///
+/// \param PartialSpec the (uninstantiated) variable template partial
+/// specialization that we are instantiating.
+///
+/// \returns The instantiated partial specialization, if successful; otherwise,
+/// NULL to indicate an error.
+VarTemplatePartialSpecializationDecl *
+TemplateDeclInstantiator::InstantiateVarTemplatePartialSpecialization(
+    VarTemplateDecl *VarTemplate,
+    VarTemplatePartialSpecializationDecl *PartialSpec) {
+  // Create a local instantiation scope for this variable template partial
+  // specialization, which will contain the instantiations of the template
+  // parameters.
+  LocalInstantiationScope Scope(SemaRef);
+
+  // Substitute into the template parameters of the variable template partial
+  // specialization.
+  TemplateParameterList *TempParams = PartialSpec->getTemplateParameters();
+  TemplateParameterList *InstParams = SubstTemplateParams(TempParams);
+  if (!InstParams)
+    return nullptr;
+
+  // Substitute into the template arguments of the variable template partial
+  // specialization.
+  const ASTTemplateArgumentListInfo *TemplArgInfo
+    = PartialSpec->getTemplateArgsAsWritten();
+  TemplateArgumentListInfo InstTemplateArgs(TemplArgInfo->LAngleLoc,
+                                            TemplArgInfo->RAngleLoc);
+  if (SemaRef.Subst(TemplArgInfo->getTemplateArgs(),
+                    TemplArgInfo->NumTemplateArgs,
+                    InstTemplateArgs, TemplateArgs))
+    return nullptr;
+
+  // Check that the template argument list is well-formed for this
+  // class template.
+  SmallVector<TemplateArgument, 4> Converted;
+  if (SemaRef.CheckTemplateArgumentList(VarTemplate, PartialSpec->getLocation(),
+                                        InstTemplateArgs, false, Converted))
+    return nullptr;
+
+  // Check these arguments are valid for a template partial specialization.
+  if (SemaRef.CheckTemplatePartialSpecializationArgs(
+          PartialSpec->getLocation(), VarTemplate, InstTemplateArgs.size(),
+          Converted))
+    return nullptr;
+
+  // Figure out where to insert this variable template partial specialization
+  // in the member template's set of variable template partial specializations.
+  void *InsertPos = nullptr;
+  VarTemplateSpecializationDecl *PrevDecl =
+      VarTemplate->findPartialSpecialization(Converted, InsertPos);
+
+  // Build the canonical type that describes the converted template
+  // arguments of the variable template partial specialization.
+  QualType CanonType = SemaRef.Context.getTemplateSpecializationType(
+      TemplateName(VarTemplate), Converted);
+
+  // Build the fully-sugared type for this variable template
+  // specialization as the user wrote in the specialization
+  // itself. This means that we'll pretty-print the type retrieved
+  // from the specialization's declaration the way that the user
+  // actually wrote the specialization, rather than formatting the
+  // name based on the "canonical" representation used to store the
+  // template arguments in the specialization.
+  TypeSourceInfo *WrittenTy = SemaRef.Context.getTemplateSpecializationTypeInfo(
+      TemplateName(VarTemplate), PartialSpec->getLocation(), InstTemplateArgs,
+      CanonType);
+
+  if (PrevDecl) {
+    // We've already seen a partial specialization with the same template
+    // parameters and template arguments. This can happen, for example, when
+    // substituting the outer template arguments ends up causing two
+    // variable template partial specializations of a member variable template
+    // to have identical forms, e.g.,
+    //
+    //   template<typename T, typename U>
+    //   struct Outer {
+    //     template<typename X, typename Y> pair<X,Y> p;
+    //     template<typename Y> pair<T, Y> p;
+    //     template<typename Y> pair<U, Y> p;
+    //   };
+    //
+    //   Outer<int, int> outer; // error: the partial specializations of Inner
+    //                          // have the same signature.
+    SemaRef.Diag(PartialSpec->getLocation(),
+                 diag::err_var_partial_spec_redeclared)
+        << WrittenTy->getType();
+    SemaRef.Diag(PrevDecl->getLocation(),
+                 diag::note_var_prev_partial_spec_here);
+    return nullptr;
+  }
+
+  // Do substitution on the type of the declaration
+  TypeSourceInfo *DI = SemaRef.SubstType(
+      PartialSpec->getTypeSourceInfo(), TemplateArgs,
+      PartialSpec->getTypeSpecStartLoc(), PartialSpec->getDeclName());
+  if (!DI)
+    return nullptr;
+
+  if (DI->getType()->isFunctionType()) {
+    SemaRef.Diag(PartialSpec->getLocation(),
+                 diag::err_variable_instantiates_to_function)
+        << PartialSpec->isStaticDataMember() << DI->getType();
+    return nullptr;
+  }
+
+  // Create the variable template partial specialization declaration.
+  VarTemplatePartialSpecializationDecl *InstPartialSpec =
+      VarTemplatePartialSpecializationDecl::Create(
+          SemaRef.Context, Owner, PartialSpec->getInnerLocStart(),
+          PartialSpec->getLocation(), InstParams, VarTemplate, DI->getType(),
+          DI, PartialSpec->getStorageClass(), Converted, InstTemplateArgs);
+
+  // Substitute the nested name specifier, if any.
+  if (SubstQualifier(PartialSpec, InstPartialSpec))
+    return nullptr;
+
+  InstPartialSpec->setInstantiatedFromMember(PartialSpec);
+  InstPartialSpec->setTypeAsWritten(WrittenTy);
+
+  // Check the completed partial specialization.
+  SemaRef.CheckTemplatePartialSpecialization(InstPartialSpec);
+
+  // Add this partial specialization to the set of variable template partial
+  // specializations. The instantiation of the initializer is not necessary.
+  VarTemplate->AddPartialSpecialization(InstPartialSpec, /*InsertPos=*/nullptr);
+
+  SemaRef.BuildVariableInstantiation(InstPartialSpec, PartialSpec, TemplateArgs,
+                                     LateAttrs, Owner, StartingScope);
+
+  return InstPartialSpec;
+}
+
+TypeSourceInfo*
+TemplateDeclInstantiator::SubstFunctionType(FunctionDecl *D,
+                              SmallVectorImpl<ParmVarDecl *> &Params) {
+  TypeSourceInfo *OldTInfo = D->getTypeSourceInfo();
+  assert(OldTInfo && "substituting function without type source info");
+  assert(Params.empty() && "parameter vector is non-empty at start");
+
+  CXXRecordDecl *ThisContext = nullptr;
+  Qualifiers ThisTypeQuals;
+  if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(D)) {
+    ThisContext = cast<CXXRecordDecl>(Owner);
+    ThisTypeQuals = Method->getMethodQualifiers();
+  }
+
+  TypeSourceInfo *NewTInfo
+    = SemaRef.SubstFunctionDeclType(OldTInfo, TemplateArgs,
+                                    D->getTypeSpecStartLoc(),
+                                    D->getDeclName(),
+                                    ThisContext, ThisTypeQuals);
+  if (!NewTInfo)
+    return nullptr;
+
+  TypeLoc OldTL = OldTInfo->getTypeLoc().IgnoreParens();
+  if (FunctionProtoTypeLoc OldProtoLoc = OldTL.getAs<FunctionProtoTypeLoc>()) {
+    if (NewTInfo != OldTInfo) {
+      // Get parameters from the new type info.
+      TypeLoc NewTL = NewTInfo->getTypeLoc().IgnoreParens();
+      FunctionProtoTypeLoc NewProtoLoc = NewTL.castAs<FunctionProtoTypeLoc>();
+      unsigned NewIdx = 0;
+      for (unsigned OldIdx = 0, NumOldParams = OldProtoLoc.getNumParams();
+           OldIdx != NumOldParams; ++OldIdx) {
+        ParmVarDecl *OldParam = OldProtoLoc.getParam(OldIdx);
+        LocalInstantiationScope *Scope = SemaRef.CurrentInstantiationScope;
+
+        Optional<unsigned> NumArgumentsInExpansion;
+        if (OldParam->isParameterPack())
+          NumArgumentsInExpansion =
+              SemaRef.getNumArgumentsInExpansion(OldParam->getType(),
+                                                 TemplateArgs);
+        if (!NumArgumentsInExpansion) {
+          // Simple case: normal parameter, or a parameter pack that's
+          // instantiated to a (still-dependent) parameter pack.
+          ParmVarDecl *NewParam = NewProtoLoc.getParam(NewIdx++);
+          Params.push_back(NewParam);
+          Scope->InstantiatedLocal(OldParam, NewParam);
+        } else {
+          // Parameter pack expansion: make the instantiation an argument pack.
+          Scope->MakeInstantiatedLocalArgPack(OldParam);
+          for (unsigned I = 0; I != *NumArgumentsInExpansion; ++I) {
+            ParmVarDecl *NewParam = NewProtoLoc.getParam(NewIdx++);
+            Params.push_back(NewParam);
+            Scope->InstantiatedLocalPackArg(OldParam, NewParam);
+          }
+        }
+      }
+    } else {
+      // The function type itself was not dependent and therefore no
+      // substitution occurred. However, we still need to instantiate
+      // the function parameters themselves.
+      const FunctionProtoType *OldProto =
+          cast<FunctionProtoType>(OldProtoLoc.getType());
+      for (unsigned i = 0, i_end = OldProtoLoc.getNumParams(); i != i_end;
+           ++i) {
+        ParmVarDecl *OldParam = OldProtoLoc.getParam(i);
+        if (!OldParam) {
+          Params.push_back(SemaRef.BuildParmVarDeclForTypedef(
+              D, D->getLocation(), OldProto->getParamType(i)));
+          continue;
+        }
+
+        ParmVarDecl *Parm =
+            cast_or_null<ParmVarDecl>(VisitParmVarDecl(OldParam));
+        if (!Parm)
+          return nullptr;
+        Params.push_back(Parm);
+      }
+    }
+  } else {
+    // If the type of this function, after ignoring parentheses, is not
+    // *directly* a function type, then we're instantiating a function that
+    // was declared via a typedef or with attributes, e.g.,
+    //
+    //   typedef int functype(int, int);
+    //   functype func;
+    //   int __cdecl meth(int, int);
+    //
+    // In this case, we'll just go instantiate the ParmVarDecls that we
+    // synthesized in the method declaration.
+    SmallVector<QualType, 4> ParamTypes;
+    Sema::ExtParameterInfoBuilder ExtParamInfos;
+    if (SemaRef.SubstParmTypes(D->getLocation(), D->parameters(), nullptr,
+                               TemplateArgs, ParamTypes, &Params,
+                               ExtParamInfos))
+      return nullptr;
+  }
+
+  return NewTInfo;
+}
+
+/// Introduce the instantiated function parameters into the local
+/// instantiation scope, and set the parameter names to those used
+/// in the template.
+static bool addInstantiatedParametersToScope(Sema &S, FunctionDecl *Function,
+                                             const FunctionDecl *PatternDecl,
+                                             LocalInstantiationScope &Scope,
+                           const MultiLevelTemplateArgumentList &TemplateArgs) {
+  unsigned FParamIdx = 0;
+  for (unsigned I = 0, N = PatternDecl->getNumParams(); I != N; ++I) {
+    const ParmVarDecl *PatternParam = PatternDecl->getParamDecl(I);
+    if (!PatternParam->isParameterPack()) {
+      // Simple case: not a parameter pack.
+      assert(FParamIdx < Function->getNumParams());
+      ParmVarDecl *FunctionParam = Function->getParamDecl(FParamIdx);
+      FunctionParam->setDeclName(PatternParam->getDeclName());
+      // If the parameter's type is not dependent, update it to match the type
+      // in the pattern. They can differ in top-level cv-qualifiers, and we want
+      // the pattern's type here. If the type is dependent, they can't differ,
+      // per core issue 1668. Substitute into the type from the pattern, in case
+      // it's instantiation-dependent.
+      // FIXME: Updating the type to work around this is at best fragile.
+      if (!PatternDecl->getType()->isDependentType()) {
+        QualType T = S.SubstType(PatternParam->getType(), TemplateArgs,
+                                 FunctionParam->getLocation(),
+                                 FunctionParam->getDeclName());
+        if (T.isNull())
+          return true;
+        FunctionParam->setType(T);
+      }
+
+      Scope.InstantiatedLocal(PatternParam, FunctionParam);
+      ++FParamIdx;
+      continue;
+    }
+
+    // Expand the parameter pack.
+    Scope.MakeInstantiatedLocalArgPack(PatternParam);
+    Optional<unsigned> NumArgumentsInExpansion
+      = S.getNumArgumentsInExpansion(PatternParam->getType(), TemplateArgs);
+    if (NumArgumentsInExpansion) {
+      QualType PatternType =
+          PatternParam->getType()->castAs<PackExpansionType>()->getPattern();
+      for (unsigned Arg = 0; Arg < *NumArgumentsInExpansion; ++Arg) {
+        ParmVarDecl *FunctionParam = Function->getParamDecl(FParamIdx);
+        FunctionParam->setDeclName(PatternParam->getDeclName());
+        if (!PatternDecl->getType()->isDependentType()) {
+          Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(S, Arg);
+          QualType T = S.SubstType(PatternType, TemplateArgs,
+                                   FunctionParam->getLocation(),
+                                   FunctionParam->getDeclName());
+          if (T.isNull())
+            return true;
+          FunctionParam->setType(T);
+        }
+
+        Scope.InstantiatedLocalPackArg(PatternParam, FunctionParam);
+        ++FParamIdx;
+      }
+    }
+  }
+
+  return false;
+}
+
+void Sema::InstantiateExceptionSpec(SourceLocation PointOfInstantiation,
+                                    FunctionDecl *Decl) {
+  const FunctionProtoType *Proto = Decl->getType()->castAs<FunctionProtoType>();
+  if (Proto->getExceptionSpecType() != EST_Uninstantiated)
+    return;
+
+  InstantiatingTemplate Inst(*this, PointOfInstantiation, Decl,
+                             InstantiatingTemplate::ExceptionSpecification());
+  if (Inst.isInvalid()) {
+    // We hit the instantiation depth limit. Clear the exception specification
+    // so that our callers don't have to cope with EST_Uninstantiated.
+    UpdateExceptionSpec(Decl, EST_None);
+    return;
+  }
+  if (Inst.isAlreadyInstantiating()) {
+    // This exception specification indirectly depends on itself. Reject.
+    // FIXME: Corresponding rule in the standard?
+    Diag(PointOfInstantiation, diag::err_exception_spec_cycle) << Decl;
+    UpdateExceptionSpec(Decl, EST_None);
+    return;
+  }
+
+  // Enter the scope of this instantiation. We don't use
+  // PushDeclContext because we don't have a scope.
+  Sema::ContextRAII savedContext(*this, Decl);
+  LocalInstantiationScope Scope(*this);
+
+  MultiLevelTemplateArgumentList TemplateArgs =
+    getTemplateInstantiationArgs(Decl, nullptr, /*RelativeToPrimary*/true);
+
+  FunctionDecl *Template = Proto->getExceptionSpecTemplate();
+  if (addInstantiatedParametersToScope(*this, Decl, Template, Scope,
+                                       TemplateArgs)) {
+    UpdateExceptionSpec(Decl, EST_None);
+    return;
+  }
+
+  SubstExceptionSpec(Decl, Template->getType()->castAs<FunctionProtoType>(),
+                     TemplateArgs);
+}
+
+/// Initializes the common fields of an instantiation function
+/// declaration (New) from the corresponding fields of its template (Tmpl).
+///
+/// \returns true if there was an error
+bool
+TemplateDeclInstantiator::InitFunctionInstantiation(FunctionDecl *New,
+                                                    FunctionDecl *Tmpl) {
+  if (Tmpl->isDeleted())
+    New->setDeletedAsWritten();
+
+  New->setImplicit(Tmpl->isImplicit());
+
+  // Forward the mangling number from the template to the instantiated decl.
+  SemaRef.Context.setManglingNumber(New,
+                                    SemaRef.Context.getManglingNumber(Tmpl));
+
+  // If we are performing substituting explicitly-specified template arguments
+  // or deduced template arguments into a function template and we reach this
+  // point, we are now past the point where SFINAE applies and have committed
+  // to keeping the new function template specialization. We therefore
+  // convert the active template instantiation for the function template
+  // into a template instantiation for this specific function template
+  // specialization, which is not a SFINAE context, so that we diagnose any
+  // further errors in the declaration itself.
+  typedef Sema::CodeSynthesisContext ActiveInstType;
+  ActiveInstType &ActiveInst = SemaRef.CodeSynthesisContexts.back();
+  if (ActiveInst.Kind == ActiveInstType::ExplicitTemplateArgumentSubstitution ||
+      ActiveInst.Kind == ActiveInstType::DeducedTemplateArgumentSubstitution) {
+    if (FunctionTemplateDecl *FunTmpl
+          = dyn_cast<FunctionTemplateDecl>(ActiveInst.Entity)) {
+      assert(FunTmpl->getTemplatedDecl() == Tmpl &&
+             "Deduction from the wrong function template?");
+      (void) FunTmpl;
+      atTemplateEnd(SemaRef.TemplateInstCallbacks, SemaRef, ActiveInst);
+      ActiveInst.Kind = ActiveInstType::TemplateInstantiation;
+      ActiveInst.Entity = New;
+      atTemplateBegin(SemaRef.TemplateInstCallbacks, SemaRef, ActiveInst);
+    }
+  }
+
+  const FunctionProtoType *Proto = Tmpl->getType()->getAs<FunctionProtoType>();
+  assert(Proto && "Function template without prototype?");
+
+  if (Proto->hasExceptionSpec() || Proto->getNoReturnAttr()) {
+    FunctionProtoType::ExtProtoInfo EPI = Proto->getExtProtoInfo();
+
+    // DR1330: In C++11, defer instantiation of a non-trivial
+    // exception specification.
+    // DR1484: Local classes and their members are instantiated along with the
+    // containing function.
+    if (SemaRef.getLangOpts().CPlusPlus11 &&
+        EPI.ExceptionSpec.Type != EST_None &&
+        EPI.ExceptionSpec.Type != EST_DynamicNone &&
+        EPI.ExceptionSpec.Type != EST_BasicNoexcept &&
+        !Tmpl->isLexicallyWithinFunctionOrMethod()) {
+      FunctionDecl *ExceptionSpecTemplate = Tmpl;
+      if (EPI.ExceptionSpec.Type == EST_Uninstantiated)
+        ExceptionSpecTemplate = EPI.ExceptionSpec.SourceTemplate;
+      ExceptionSpecificationType NewEST = EST_Uninstantiated;
+      if (EPI.ExceptionSpec.Type == EST_Unevaluated)
+        NewEST = EST_Unevaluated;
+
+      // Mark the function has having an uninstantiated exception specification.
+      const FunctionProtoType *NewProto
+        = New->getType()->getAs<FunctionProtoType>();
+      assert(NewProto && "Template instantiation without function prototype?");
+      EPI = NewProto->getExtProtoInfo();
+      EPI.ExceptionSpec.Type = NewEST;
+      EPI.ExceptionSpec.SourceDecl = New;
+      EPI.ExceptionSpec.SourceTemplate = ExceptionSpecTemplate;
+      New->setType(SemaRef.Context.getFunctionType(
+          NewProto->getReturnType(), NewProto->getParamTypes(), EPI));
+    } else {
+      Sema::ContextRAII SwitchContext(SemaRef, New);
+      SemaRef.SubstExceptionSpec(New, Proto, TemplateArgs);
+    }
+  }
+
+  // Get the definition. Leaves the variable unchanged if undefined.
+  const FunctionDecl *Definition = Tmpl;
+  Tmpl->isDefined(Definition);
+
+  SemaRef.InstantiateAttrs(TemplateArgs, Definition, New,
+                           LateAttrs, StartingScope);
+
+  return false;
+}
+
+/// Initializes common fields of an instantiated method
+/// declaration (New) from the corresponding fields of its template
+/// (Tmpl).
+///
+/// \returns true if there was an error
+bool
+TemplateDeclInstantiator::InitMethodInstantiation(CXXMethodDecl *New,
+                                                  CXXMethodDecl *Tmpl) {
+  if (InitFunctionInstantiation(New, Tmpl))
+    return true;
+
+  if (isa<CXXDestructorDecl>(New) && SemaRef.getLangOpts().CPlusPlus11)
+    SemaRef.AdjustDestructorExceptionSpec(cast<CXXDestructorDecl>(New));
+
+  New->setAccess(Tmpl->getAccess());
+  if (Tmpl->isVirtualAsWritten())
+    New->setVirtualAsWritten(true);
+
+  // FIXME: New needs a pointer to Tmpl
+  return false;
+}
+
+/// Instantiate (or find existing instantiation of) a function template with a
+/// given set of template arguments.
+///
+/// Usually this should not be used, and template argument deduction should be
+/// used in its place.
+FunctionDecl *
+Sema::InstantiateFunctionDeclaration(FunctionTemplateDecl *FTD,
+                                     const TemplateArgumentList *Args,
+                                     SourceLocation Loc) {
+  FunctionDecl *FD = FTD->getTemplatedDecl();
+
+  sema::TemplateDeductionInfo Info(Loc);
+  InstantiatingTemplate Inst(
+      *this, Loc, FTD, Args->asArray(),
+      CodeSynthesisContext::ExplicitTemplateArgumentSubstitution, Info);
+  if (Inst.isInvalid())
+    return nullptr;
+
+  ContextRAII SavedContext(*this, FD);
+  MultiLevelTemplateArgumentList MArgs(*Args);
+
+  return cast_or_null<FunctionDecl>(SubstDecl(FD, FD->getParent(), MArgs));
+}
+
+/// In the MS ABI, we need to instantiate default arguments of dllexported
+/// default constructors along with the constructor definition. This allows IR
+/// gen to emit a constructor closure which calls the default constructor with
+/// its default arguments.
+static void InstantiateDefaultCtorDefaultArgs(Sema &S,
+                                              CXXConstructorDecl *Ctor) {
+  assert(S.Context.getTargetInfo().getCXXABI().isMicrosoft() &&
+         Ctor->isDefaultConstructor());
+  unsigned NumParams = Ctor->getNumParams();
+  if (NumParams == 0)
+    return;
+  DLLExportAttr *Attr = Ctor->getAttr<DLLExportAttr>();
+  if (!Attr)
+    return;
+  for (unsigned I = 0; I != NumParams; ++I) {
+    (void)S.CheckCXXDefaultArgExpr(Attr->getLocation(), Ctor,
+                                   Ctor->getParamDecl(I));
+    S.DiscardCleanupsInEvaluationContext();
+  }
+}
+
+/// Instantiate the definition of the given function from its
+/// template.
+///
+/// \param PointOfInstantiation the point at which the instantiation was
+/// required. Note that this is not precisely a "point of instantiation"
+/// for the function, but it's close.
+///
+/// \param Function the already-instantiated declaration of a
+/// function template specialization or member function of a class template
+/// specialization.
+///
+/// \param Recursive if true, recursively instantiates any functions that
+/// are required by this instantiation.
+///
+/// \param DefinitionRequired if true, then we are performing an explicit
+/// instantiation where the body of the function is required. Complain if
+/// there is no such body.
+void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
+                                         FunctionDecl *Function,
+                                         bool Recursive,
+                                         bool DefinitionRequired,
+                                         bool AtEndOfTU) {
+  if (Function->isInvalidDecl() || Function->isDefined() ||
+      isa<CXXDeductionGuideDecl>(Function))
+    return;
+
+  // Never instantiate an explicit specialization except if it is a class scope
+  // explicit specialization.
+  TemplateSpecializationKind TSK =
+      Function->getTemplateSpecializationKindForInstantiation();
+  if (TSK == TSK_ExplicitSpecialization)
+    return;
+
+  // Find the function body that we'll be substituting.
+  const FunctionDecl *PatternDecl = Function->getTemplateInstantiationPattern();
+  assert(PatternDecl && "instantiating a non-template");
+
+  const FunctionDecl *PatternDef = PatternDecl->getDefinition();
+  Stmt *Pattern = nullptr;
+  if (PatternDef) {
+    Pattern = PatternDef->getBody(PatternDef);
+    PatternDecl = PatternDef;
+    if (PatternDef->willHaveBody())
+      PatternDef = nullptr;
+  }
+
+  // FIXME: We need to track the instantiation stack in order to know which
+  // definitions should be visible within this instantiation.
+  if (DiagnoseUninstantiableTemplate(PointOfInstantiation, Function,
+                                Function->getInstantiatedFromMemberFunction(),
+                                     PatternDecl, PatternDef, TSK,
+                                     /*Complain*/DefinitionRequired)) {
+    if (DefinitionRequired)
+      Function->setInvalidDecl();
+    else if (TSK == TSK_ExplicitInstantiationDefinition) {
+      // Try again at the end of the translation unit (at which point a
+      // definition will be required).
+      assert(!Recursive);
+      Function->setInstantiationIsPending(true);
+      PendingInstantiations.push_back(
+        std::make_pair(Function, PointOfInstantiation));
+    } else if (TSK == TSK_ImplicitInstantiation) {
+      if (AtEndOfTU && !getDiagnostics().hasErrorOccurred() &&
+          !getSourceManager().isInSystemHeader(PatternDecl->getBeginLoc())) {
+        Diag(PointOfInstantiation, diag::warn_func_template_missing)
+          << Function;
+        Diag(PatternDecl->getLocation(), diag::note_forward_template_decl);
+        if (getLangOpts().CPlusPlus11)
+          Diag(PointOfInstantiation, diag::note_inst_declaration_hint)
+            << Function;
+      }
+    }
+
+    return;
+  }
+
+  // Postpone late parsed template instantiations.
+  if (PatternDecl->isLateTemplateParsed() &&
+      !LateTemplateParser) {
+    Function->setInstantiationIsPending(true);
+    LateParsedInstantiations.push_back(
+        std::make_pair(Function, PointOfInstantiation));
+    return;
+  }
+
+  llvm::TimeTraceScope TimeScope("InstantiateFunction", [&]() {
+    std::string Name;
+    llvm::raw_string_ostream OS(Name);
+    Function->getNameForDiagnostic(OS, getPrintingPolicy(),
+                                   /*Qualified=*/true);
+    return Name;
+  });
+
+  // If we're performing recursive template instantiation, create our own
+  // queue of pending implicit instantiations that we will instantiate later,
+  // while we're still within our own instantiation context.
+  // This has to happen before LateTemplateParser below is called, so that
+  // it marks vtables used in late parsed templates as used.
+  GlobalEagerInstantiationScope GlobalInstantiations(*this,
+                                                     /*Enabled=*/Recursive);
+  LocalEagerInstantiationScope LocalInstantiations(*this);
+
+  // Call the LateTemplateParser callback if there is a need to late parse
+  // a templated function definition.
+  if (!Pattern && PatternDecl->isLateTemplateParsed() &&
+      LateTemplateParser) {
+    // FIXME: Optimize to allow individual templates to be deserialized.
+    if (PatternDecl->isFromASTFile())
+      ExternalSource->ReadLateParsedTemplates(LateParsedTemplateMap);
+
+    auto LPTIter = LateParsedTemplateMap.find(PatternDecl);
+    assert(LPTIter != LateParsedTemplateMap.end() &&
+           "missing LateParsedTemplate");
+    LateTemplateParser(OpaqueParser, *LPTIter->second);
+    Pattern = PatternDecl->getBody(PatternDecl);
+  }
+
+  // Note, we should never try to instantiate a deleted function template.
+  assert((Pattern || PatternDecl->isDefaulted() ||
+          PatternDecl->hasSkippedBody()) &&
+         "unexpected kind of function template definition");
+
+  // C++1y [temp.explicit]p10:
+  //   Except for inline functions, declarations with types deduced from their
+  //   initializer or return value, and class template specializations, other
+  //   explicit instantiation declarations have the effect of suppressing the
+  //   implicit instantiation of the entity to which they refer.
+  if (TSK == TSK_ExplicitInstantiationDeclaration &&
+      !PatternDecl->isInlined() &&
+      !PatternDecl->getReturnType()->getContainedAutoType())
+    return;
+
+  if (PatternDecl->isInlined()) {
+    // Function, and all later redeclarations of it (from imported modules,
+    // for instance), are now implicitly inline.
+    for (auto *D = Function->getMostRecentDecl(); /**/;
+         D = D->getPreviousDecl()) {
+      D->setImplicitlyInline();
+      if (D == Function)
+        break;
+    }
+  }
+
+  InstantiatingTemplate Inst(*this, PointOfInstantiation, Function);
+  if (Inst.isInvalid() || Inst.isAlreadyInstantiating())
+    return;
+  PrettyDeclStackTraceEntry CrashInfo(Context, Function, SourceLocation(),
+                                      "instantiating function definition");
+
+  // The instantiation is visible here, even if it was first declared in an
+  // unimported module.
+  Function->setVisibleDespiteOwningModule();
+
+  // Copy the inner loc start from the pattern.
+  Function->setInnerLocStart(PatternDecl->getInnerLocStart());
+
+  EnterExpressionEvaluationContext EvalContext(
+      *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
+
+  // Introduce a new scope where local variable instantiations will be
+  // recorded, unless we're actually a member function within a local
+  // class, in which case we need to merge our results with the parent
+  // scope (of the enclosing function).
+  bool MergeWithParentScope = false;
+  if (CXXRecordDecl *Rec = dyn_cast<CXXRecordDecl>(Function->getDeclContext()))
+    MergeWithParentScope = Rec->isLocalClass();
+
+  LocalInstantiationScope Scope(*this, MergeWithParentScope);
+
+  if (PatternDecl->isDefaulted())
+    SetDeclDefaulted(Function, PatternDecl->getLocation());
+  else {
+    MultiLevelTemplateArgumentList TemplateArgs =
+      getTemplateInstantiationArgs(Function, nullptr, false, PatternDecl);
+
+    // Substitute into the qualifier; we can get a substitution failure here
+    // through evil use of alias templates.
+    // FIXME: Is CurContext correct for this? Should we go to the (instantiation
+    // of the) lexical context of the pattern?
+    SubstQualifier(*this, PatternDecl, Function, TemplateArgs);
+
+    ActOnStartOfFunctionDef(nullptr, Function);
+
+    // Enter the scope of this instantiation. We don't use
+    // PushDeclContext because we don't have a scope.
+    Sema::ContextRAII savedContext(*this, Function);
+
+    if (addInstantiatedParametersToScope(*this, Function, PatternDecl, Scope,
+                                         TemplateArgs))
+      return;
+
+    StmtResult Body;
+    if (PatternDecl->hasSkippedBody()) {
+      ActOnSkippedFunctionBody(Function);
+      Body = nullptr;
+    } else {
+      if (CXXConstructorDecl *Ctor = dyn_cast<CXXConstructorDecl>(Function)) {
+        // If this is a constructor, instantiate the member initializers.
+        InstantiateMemInitializers(Ctor, cast<CXXConstructorDecl>(PatternDecl),
+                                   TemplateArgs);
+
+        // If this is an MS ABI dllexport default constructor, instantiate any
+        // default arguments.
+        if (Context.getTargetInfo().getCXXABI().isMicrosoft() &&
+            Ctor->isDefaultConstructor()) {
+          InstantiateDefaultCtorDefaultArgs(*this, Ctor);
+        }
+      }
+
+      // Instantiate the function body.
+      Body = SubstStmt(Pattern, TemplateArgs);
+
+      if (Body.isInvalid())
+        Function->setInvalidDecl();
+    }
+    // FIXME: finishing the function body while in an expression evaluation
+    // context seems wrong. Investigate more.
+    ActOnFinishFunctionBody(Function, Body.get(), /*IsInstantiation=*/true);
+
+    PerformDependentDiagnostics(PatternDecl, TemplateArgs);
+
+    if (auto *Listener = getASTMutationListener())
+      Listener->FunctionDefinitionInstantiated(Function);
+
+    savedContext.pop();
+  }
+
+  DeclGroupRef DG(Function);
+  Consumer.HandleTopLevelDecl(DG);
+
+  // This class may have local implicit instantiations that need to be
+  // instantiation within this scope.
+  LocalInstantiations.perform();
+  Scope.Exit();
+  GlobalInstantiations.perform();
+}
+
+VarTemplateSpecializationDecl *Sema::BuildVarTemplateInstantiation(
+    VarTemplateDecl *VarTemplate, VarDecl *FromVar,
+    const TemplateArgumentList &TemplateArgList,
+    const TemplateArgumentListInfo &TemplateArgsInfo,
+    SmallVectorImpl<TemplateArgument> &Converted,
+    SourceLocation PointOfInstantiation, void *InsertPos,
+    LateInstantiatedAttrVec *LateAttrs,
+    LocalInstantiationScope *StartingScope) {
+  if (FromVar->isInvalidDecl())
+    return nullptr;
+
+  InstantiatingTemplate Inst(*this, PointOfInstantiation, FromVar);
+  if (Inst.isInvalid())
+    return nullptr;
+
+  MultiLevelTemplateArgumentList TemplateArgLists;
+  TemplateArgLists.addOuterTemplateArguments(&TemplateArgList);
+
+  // Instantiate the first declaration of the variable template: for a partial
+  // specialization of a static data member template, the first declaration may
+  // or may not be the declaration in the class; if it's in the class, we want
+  // to instantiate a member in the class (a declaration), and if it's outside,
+  // we want to instantiate a definition.
+  //
+  // If we're instantiating an explicitly-specialized member template or member
+  // partial specialization, don't do this. The member specialization completely
+  // replaces the original declaration in this case.
+  bool IsMemberSpec = false;
+  if (VarTemplatePartialSpecializationDecl *PartialSpec =
+          dyn_cast<VarTemplatePartialSpecializationDecl>(FromVar))
+    IsMemberSpec = PartialSpec->isMemberSpecialization();
+  else if (VarTemplateDecl *FromTemplate = FromVar->getDescribedVarTemplate())
+    IsMemberSpec = FromTemplate->isMemberSpecialization();
+  if (!IsMemberSpec)
+    FromVar = FromVar->getFirstDecl();
+
+  MultiLevelTemplateArgumentList MultiLevelList(TemplateArgList);
+  TemplateDeclInstantiator Instantiator(*this, FromVar->getDeclContext(),
+                                        MultiLevelList);
+
+  // TODO: Set LateAttrs and StartingScope ...
+
+  return cast_or_null<VarTemplateSpecializationDecl>(
+      Instantiator.VisitVarTemplateSpecializationDecl(
+          VarTemplate, FromVar, InsertPos, TemplateArgsInfo, Converted));
+}
+
+/// Instantiates a variable template specialization by completing it
+/// with appropriate type information and initializer.
+VarTemplateSpecializationDecl *Sema::CompleteVarTemplateSpecializationDecl(
+    VarTemplateSpecializationDecl *VarSpec, VarDecl *PatternDecl,
+    const MultiLevelTemplateArgumentList &TemplateArgs) {
+  assert(PatternDecl->isThisDeclarationADefinition() &&
+         "don't have a definition to instantiate from");
+
+  // Do substitution on the type of the declaration
+  TypeSourceInfo *DI =
+      SubstType(PatternDecl->getTypeSourceInfo(), TemplateArgs,
+                PatternDecl->getTypeSpecStartLoc(), PatternDecl->getDeclName());
+  if (!DI)
+    return nullptr;
+
+  // Update the type of this variable template specialization.
+  VarSpec->setType(DI->getType());
+
+  // Convert the declaration into a definition now.
+  VarSpec->setCompleteDefinition();
+
+  // Instantiate the initializer.
+  InstantiateVariableInitializer(VarSpec, PatternDecl, TemplateArgs);
+
+  return VarSpec;
+}
+
+/// BuildVariableInstantiation - Used after a new variable has been created.
+/// Sets basic variable data and decides whether to postpone the
+/// variable instantiation.
+void Sema::BuildVariableInstantiation(
+    VarDecl *NewVar, VarDecl *OldVar,
+    const MultiLevelTemplateArgumentList &TemplateArgs,
+    LateInstantiatedAttrVec *LateAttrs, DeclContext *Owner,
+    LocalInstantiationScope *StartingScope,
+    bool InstantiatingVarTemplate,
+    VarTemplateSpecializationDecl *PrevDeclForVarTemplateSpecialization) {
+  // Instantiating a partial specialization to produce a partial
+  // specialization.
+  bool InstantiatingVarTemplatePartialSpec =
+      isa<VarTemplatePartialSpecializationDecl>(OldVar) &&
+      isa<VarTemplatePartialSpecializationDecl>(NewVar);
+  // Instantiating from a variable template (or partial specialization) to
+  // produce a variable template specialization.
+  bool InstantiatingSpecFromTemplate =
+      isa<VarTemplateSpecializationDecl>(NewVar) &&
+      (OldVar->getDescribedVarTemplate() ||
+       isa<VarTemplatePartialSpecializationDecl>(OldVar));
+
+  // If we are instantiating a local extern declaration, the
+  // instantiation belongs lexically to the containing function.
+  // If we are instantiating a static data member defined
+  // out-of-line, the instantiation will have the same lexical
+  // context (which will be a namespace scope) as the template.
+  if (OldVar->isLocalExternDecl()) {
+    NewVar->setLocalExternDecl();
+    NewVar->setLexicalDeclContext(Owner);
+  } else if (OldVar->isOutOfLine())
+    NewVar->setLexicalDeclContext(OldVar->getLexicalDeclContext());
+  NewVar->setTSCSpec(OldVar->getTSCSpec());
+  NewVar->setInitStyle(OldVar->getInitStyle());
+  NewVar->setCXXForRangeDecl(OldVar->isCXXForRangeDecl());
+  NewVar->setObjCForDecl(OldVar->isObjCForDecl());
+  NewVar->setConstexpr(OldVar->isConstexpr());
+  NewVar->setInitCapture(OldVar->isInitCapture());
+  NewVar->setPreviousDeclInSameBlockScope(
+      OldVar->isPreviousDeclInSameBlockScope());
+  NewVar->setAccess(OldVar->getAccess());
+
+  if (!OldVar->isStaticDataMember()) {
+    if (OldVar->isUsed(false))
+      NewVar->setIsUsed();
+    NewVar->setReferenced(OldVar->isReferenced());
+  }
+
+  InstantiateAttrs(TemplateArgs, OldVar, NewVar, LateAttrs, StartingScope);
+
+  LookupResult Previous(
+      *this, NewVar->getDeclName(), NewVar->getLocation(),
+      NewVar->isLocalExternDecl() ? Sema::LookupRedeclarationWithLinkage
+                                  : Sema::LookupOrdinaryName,
+      NewVar->isLocalExternDecl() ? Sema::ForExternalRedeclaration
+                                  : forRedeclarationInCurContext());
+
+  if (NewVar->isLocalExternDecl() && OldVar->getPreviousDecl() &&
+      (!OldVar->getPreviousDecl()->getDeclContext()->isDependentContext() ||
+       OldVar->getPreviousDecl()->getDeclContext()==OldVar->getDeclContext())) {
+    // We have a previous declaration. Use that one, so we merge with the
+    // right type.
+    if (NamedDecl *NewPrev = FindInstantiatedDecl(
+            NewVar->getLocation(), OldVar->getPreviousDecl(), TemplateArgs))
+      Previous.addDecl(NewPrev);
+  } else if (!isa<VarTemplateSpecializationDecl>(NewVar) &&
+             OldVar->hasLinkage()) {
+    LookupQualifiedName(Previous, NewVar->getDeclContext(), false);
+  } else if (PrevDeclForVarTemplateSpecialization) {
+    Previous.addDecl(PrevDeclForVarTemplateSpecialization);
+  }
+  CheckVariableDeclaration(NewVar, Previous);
+
+  if (!InstantiatingVarTemplate) {
+    NewVar->getLexicalDeclContext()->addHiddenDecl(NewVar);
+    if (!NewVar->isLocalExternDecl() || !NewVar->getPreviousDecl())
+      NewVar->getDeclContext()->makeDeclVisibleInContext(NewVar);
+  }
+
+  if (!OldVar->isOutOfLine()) {
+    if (NewVar->getDeclContext()->isFunctionOrMethod())
+      CurrentInstantiationScope->InstantiatedLocal(OldVar, NewVar);
+  }
+
+  // Link instantiations of static data members back to the template from
+  // which they were instantiated.
+  //
+  // Don't do this when instantiating a template (we link the template itself
+  // back in that case) nor when instantiating a static data member template
+  // (that's not a member specialization).
+  if (NewVar->isStaticDataMember() && !InstantiatingVarTemplate &&
+      !InstantiatingSpecFromTemplate)
+    NewVar->setInstantiationOfStaticDataMember(OldVar,
+                                               TSK_ImplicitInstantiation);
+
+  // If the pattern is an (in-class) explicit specialization, then the result
+  // is also an explicit specialization.
+  if (VarTemplateSpecializationDecl *OldVTSD =
+          dyn_cast<VarTemplateSpecializationDecl>(OldVar)) {
+    if (OldVTSD->getSpecializationKind() == TSK_ExplicitSpecialization &&
+        !isa<VarTemplatePartialSpecializationDecl>(OldVTSD))
+      cast<VarTemplateSpecializationDecl>(NewVar)->setSpecializationKind(
+          TSK_ExplicitSpecialization);
+  }
+
+  // Forward the mangling number from the template to the instantiated decl.
+  Context.setManglingNumber(NewVar, Context.getManglingNumber(OldVar));
+  Context.setStaticLocalNumber(NewVar, Context.getStaticLocalNumber(OldVar));
+
+  // Figure out whether to eagerly instantiate the initializer.
+  if (InstantiatingVarTemplate || InstantiatingVarTemplatePartialSpec) {
+    // We're producing a template. Don't instantiate the initializer yet.
+  } else if (NewVar->getType()->isUndeducedType()) {
+    // We need the type to complete the declaration of the variable.
+    InstantiateVariableInitializer(NewVar, OldVar, TemplateArgs);
+  } else if (InstantiatingSpecFromTemplate ||
+             (OldVar->isInline() && OldVar->isThisDeclarationADefinition() &&
+              !NewVar->isThisDeclarationADefinition())) {
+    // Delay instantiation of the initializer for variable template
+    // specializations or inline static data members until a definition of the
+    // variable is needed.
+  } else {
+    InstantiateVariableInitializer(NewVar, OldVar, TemplateArgs);
+  }
+
+  // Diagnose unused local variables with dependent types, where the diagnostic
+  // will have been deferred.
+  if (!NewVar->isInvalidDecl() &&
+      NewVar->getDeclContext()->isFunctionOrMethod() &&
+      OldVar->getType()->isDependentType())
+    DiagnoseUnusedDecl(NewVar);
+}
+
+/// Instantiate the initializer of a variable.
+void Sema::InstantiateVariableInitializer(
+    VarDecl *Var, VarDecl *OldVar,
+    const MultiLevelTemplateArgumentList &TemplateArgs) {
+  if (ASTMutationListener *L = getASTContext().getASTMutationListener())
+    L->VariableDefinitionInstantiated(Var);
+
+  // We propagate the 'inline' flag with the initializer, because it
+  // would otherwise imply that the variable is a definition for a
+  // non-static data member.
+  if (OldVar->isInlineSpecified())
+    Var->setInlineSpecified();
+  else if (OldVar->isInline())
+    Var->setImplicitlyInline();
+
+  if (OldVar->getInit()) {
+    EnterExpressionEvaluationContext Evaluated(
+        *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated, Var);
+
+    // Instantiate the initializer.
+    ExprResult Init;
+
+    {
+      ContextRAII SwitchContext(*this, Var->getDeclContext());
+      Init = SubstInitializer(OldVar->getInit(), TemplateArgs,
+                              OldVar->getInitStyle() == VarDecl::CallInit);
+    }
+
+    if (!Init.isInvalid()) {
+      Expr *InitExpr = Init.get();
+
+      if (Var->hasAttr<DLLImportAttr>() &&
+          (!InitExpr ||
+           !InitExpr->isConstantInitializer(getASTContext(), false))) {
+        // Do not dynamically initialize dllimport variables.
+      } else if (InitExpr) {
+        bool DirectInit = OldVar->isDirectInit();
+        AddInitializerToDecl(Var, InitExpr, DirectInit);
+      } else
+        ActOnUninitializedDecl(Var);
+    } else {
+      // FIXME: Not too happy about invalidating the declaration
+      // because of a bogus initializer.
+      Var->setInvalidDecl();
+    }
+  } else {
+    // `inline` variables are a definition and declaration all in one; we won't
+    // pick up an initializer from anywhere else.
+    if (Var->isStaticDataMember() && !Var->isInline()) {
+      if (!Var->isOutOfLine())
+        return;
+
+      // If the declaration inside the class had an initializer, don't add
+      // another one to the out-of-line definition.
+      if (OldVar->getFirstDecl()->hasInit())
+        return;
+    }
+
+    // We'll add an initializer to a for-range declaration later.
+    if (Var->isCXXForRangeDecl() || Var->isObjCForDecl())
+      return;
+
+    ActOnUninitializedDecl(Var);
+  }
+
+  if (getLangOpts().CUDA)
+    checkAllowedCUDAInitializer(Var);
+}
+
+/// Instantiate the definition of the given variable from its
+/// template.
+///
+/// \param PointOfInstantiation the point at which the instantiation was
+/// required. Note that this is not precisely a "point of instantiation"
+/// for the variable, but it's close.
+///
+/// \param Var the already-instantiated declaration of a templated variable.
+///
+/// \param Recursive if true, recursively instantiates any functions that
+/// are required by this instantiation.
+///
+/// \param DefinitionRequired if true, then we are performing an explicit
+/// instantiation where a definition of the variable is required. Complain
+/// if there is no such definition.
+void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
+                                         VarDecl *Var, bool Recursive,
+                                      bool DefinitionRequired, bool AtEndOfTU) {
+  if (Var->isInvalidDecl())
+    return;
+
+  // Never instantiate an explicitly-specialized entity.
+  TemplateSpecializationKind TSK =
+      Var->getTemplateSpecializationKindForInstantiation();
+  if (TSK == TSK_ExplicitSpecialization)
+    return;
+
+  // Find the pattern and the arguments to substitute into it.
+  VarDecl *PatternDecl = Var->getTemplateInstantiationPattern();
+  assert(PatternDecl && "no pattern for templated variable");
+  MultiLevelTemplateArgumentList TemplateArgs =
+      getTemplateInstantiationArgs(Var);
+
+  VarTemplateSpecializationDecl *VarSpec =
+      dyn_cast<VarTemplateSpecializationDecl>(Var);
+  if (VarSpec) {
+    // If this is a variable template specialization, make sure that it is
+    // non-dependent.
+    bool InstantiationDependent = false;
+    assert(!TemplateSpecializationType::anyDependentTemplateArguments(
+               VarSpec->getTemplateArgsInfo(), InstantiationDependent) &&
+           "Only instantiate variable template specializations that are "
+           "not type-dependent");
+    (void)InstantiationDependent;
+
+    // If this is a static data member template, there might be an
+    // uninstantiated initializer on the declaration. If so, instantiate
+    // it now.
+    //
+    // FIXME: This largely duplicates what we would do below. The difference
+    // is that along this path we may instantiate an initializer from an
+    // in-class declaration of the template and instantiate the definition
+    // from a separate out-of-class definition.
+    if (PatternDecl->isStaticDataMember() &&
+        (PatternDecl = PatternDecl->getFirstDecl())->hasInit() &&
+        !Var->hasInit()) {
+      // FIXME: Factor out the duplicated instantiation context setup/tear down
+      // code here.
+      InstantiatingTemplate Inst(*this, PointOfInstantiation, Var);
+      if (Inst.isInvalid() || Inst.isAlreadyInstantiating())
+        return;
+      PrettyDeclStackTraceEntry CrashInfo(Context, Var, SourceLocation(),
+                                          "instantiating variable initializer");
+
+      // The instantiation is visible here, even if it was first declared in an
+      // unimported module.
+      Var->setVisibleDespiteOwningModule();
+
+      // If we're performing recursive template instantiation, create our own
+      // queue of pending implicit instantiations that we will instantiate
+      // later, while we're still within our own instantiation context.
+      GlobalEagerInstantiationScope GlobalInstantiations(*this,
+                                                         /*Enabled=*/Recursive);
+      LocalInstantiationScope Local(*this);
+      LocalEagerInstantiationScope LocalInstantiations(*this);
+
+      // Enter the scope of this instantiation. We don't use
+      // PushDeclContext because we don't have a scope.
+      ContextRAII PreviousContext(*this, Var->getDeclContext());
+      InstantiateVariableInitializer(Var, PatternDecl, TemplateArgs);
+      PreviousContext.pop();
+
+      // This variable may have local implicit instantiations that need to be
+      // instantiated within this scope.
+      LocalInstantiations.perform();
+      Local.Exit();
+      GlobalInstantiations.perform();
+    }
+  } else {
+    assert(Var->isStaticDataMember() && PatternDecl->isStaticDataMember() &&
+           "not a static data member?");
+  }
+
+  VarDecl *Def = PatternDecl->getDefinition(getASTContext());
+
+  // If we don't have a definition of the variable template, we won't perform
+  // any instantiation. Rather, we rely on the user to instantiate this
+  // definition (or provide a specialization for it) in another translation
+  // unit.
+  if (!Def && !DefinitionRequired) {
+    if (TSK == TSK_ExplicitInstantiationDefinition) {
+      PendingInstantiations.push_back(
+        std::make_pair(Var, PointOfInstantiation));
+    } else if (TSK == TSK_ImplicitInstantiation) {
+      // Warn about missing definition at the end of translation unit.
+      if (AtEndOfTU && !getDiagnostics().hasErrorOccurred() &&
+          !getSourceManager().isInSystemHeader(PatternDecl->getBeginLoc())) {
+        Diag(PointOfInstantiation, diag::warn_var_template_missing)
+          << Var;
+        Diag(PatternDecl->getLocation(), diag::note_forward_template_decl);
+        if (getLangOpts().CPlusPlus11)
+          Diag(PointOfInstantiation, diag::note_inst_declaration_hint) << Var;
+      }
+      return;
+    }
+  }
+
+  // FIXME: We need to track the instantiation stack in order to know which
+  // definitions should be visible within this instantiation.
+  // FIXME: Produce diagnostics when Var->getInstantiatedFromStaticDataMember().
+  if (DiagnoseUninstantiableTemplate(PointOfInstantiation, Var,
+                                     /*InstantiatedFromMember*/false,
+                                     PatternDecl, Def, TSK,
+                                     /*Complain*/DefinitionRequired))
+    return;
+
+  // C++11 [temp.explicit]p10:
+  //   Except for inline functions, const variables of literal types, variables
+  //   of reference types, [...] explicit instantiation declarations
+  //   have the effect of suppressing the implicit instantiation of the entity
+  //   to which they refer.
+  //
+  // FIXME: That's not exactly the same as "might be usable in constant
+  // expressions", which only allows constexpr variables and const integral
+  // types, not arbitrary const literal types.
+  if (TSK == TSK_ExplicitInstantiationDeclaration &&
+      !Var->mightBeUsableInConstantExpressions(getASTContext()))
+    return;
+
+  // Make sure to pass the instantiated variable to the consumer at the end.
+  struct PassToConsumerRAII {
+    ASTConsumer &Consumer;
+    VarDecl *Var;
+
+    PassToConsumerRAII(ASTConsumer &Consumer, VarDecl *Var)
+      : Consumer(Consumer), Var(Var) { }
+
+    ~PassToConsumerRAII() {
+      Consumer.HandleCXXStaticMemberVarInstantiation(Var);
+    }
+  } PassToConsumerRAII(Consumer, Var);
+
+  // If we already have a definition, we're done.
+  if (VarDecl *Def = Var->getDefinition()) {
+    // We may be explicitly instantiating something we've already implicitly
+    // instantiated.
+    Def->setTemplateSpecializationKind(Var->getTemplateSpecializationKind(),
+                                       PointOfInstantiation);
+    return;
+  }
+
+  InstantiatingTemplate Inst(*this, PointOfInstantiation, Var);
+  if (Inst.isInvalid() || Inst.isAlreadyInstantiating())
+    return;
+  PrettyDeclStackTraceEntry CrashInfo(Context, Var, SourceLocation(),
+                                      "instantiating variable definition");
+
+  // If we're performing recursive template instantiation, create our own
+  // queue of pending implicit instantiations that we will instantiate later,
+  // while we're still within our own instantiation context.
+  GlobalEagerInstantiationScope GlobalInstantiations(*this,
+                                                     /*Enabled=*/Recursive);
+
+  // Enter the scope of this instantiation. We don't use
+  // PushDeclContext because we don't have a scope.
+  ContextRAII PreviousContext(*this, Var->getDeclContext());
+  LocalInstantiationScope Local(*this);
+
+  LocalEagerInstantiationScope LocalInstantiations(*this);
+
+  VarDecl *OldVar = Var;
+  if (Def->isStaticDataMember() && !Def->isOutOfLine()) {
+    // We're instantiating an inline static data member whose definition was
+    // provided inside the class.
+    InstantiateVariableInitializer(Var, Def, TemplateArgs);
+  } else if (!VarSpec) {
+    Var = cast_or_null<VarDecl>(SubstDecl(Def, Var->getDeclContext(),
+                                          TemplateArgs));
+  } else if (Var->isStaticDataMember() &&
+             Var->getLexicalDeclContext()->isRecord()) {
+    // We need to instantiate the definition of a static data member template,
+    // and all we have is the in-class declaration of it. Instantiate a separate
+    // declaration of the definition.
+    TemplateDeclInstantiator Instantiator(*this, Var->getDeclContext(),
+                                          TemplateArgs);
+    Var = cast_or_null<VarDecl>(Instantiator.VisitVarTemplateSpecializationDecl(
+        VarSpec->getSpecializedTemplate(), Def, nullptr,
+        VarSpec->getTemplateArgsInfo(), VarSpec->getTemplateArgs().asArray()));
+    if (Var) {
+      llvm::PointerUnion<VarTemplateDecl *,
+                         VarTemplatePartialSpecializationDecl *> PatternPtr =
+          VarSpec->getSpecializedTemplateOrPartial();
+      if (VarTemplatePartialSpecializationDecl *Partial =
+          PatternPtr.dyn_cast<VarTemplatePartialSpecializationDecl *>())
+        cast<VarTemplateSpecializationDecl>(Var)->setInstantiationOf(
+            Partial, &VarSpec->getTemplateInstantiationArgs());
+
+      // Merge the definition with the declaration.
+      LookupResult R(*this, Var->getDeclName(), Var->getLocation(),
+                     LookupOrdinaryName, forRedeclarationInCurContext());
+      R.addDecl(OldVar);
+      MergeVarDecl(Var, R);
+
+      // Attach the initializer.
+      InstantiateVariableInitializer(Var, Def, TemplateArgs);
+    }
+  } else
+    // Complete the existing variable's definition with an appropriately
+    // substituted type and initializer.
+    Var = CompleteVarTemplateSpecializationDecl(VarSpec, Def, TemplateArgs);
+
+  PreviousContext.pop();
+
+  if (Var) {
+    PassToConsumerRAII.Var = Var;
+    Var->setTemplateSpecializationKind(OldVar->getTemplateSpecializationKind(),
+                                       OldVar->getPointOfInstantiation());
+  }
+
+  // This variable may have local implicit instantiations that need to be
+  // instantiated within this scope.
+  LocalInstantiations.perform();
+  Local.Exit();
+  GlobalInstantiations.perform();
+}
+
+void
+Sema::InstantiateMemInitializers(CXXConstructorDecl *New,
+                                 const CXXConstructorDecl *Tmpl,
+                           const MultiLevelTemplateArgumentList &TemplateArgs) {
+
+  SmallVector<CXXCtorInitializer*, 4> NewInits;
+  bool AnyErrors = Tmpl->isInvalidDecl();
+
+  // Instantiate all the initializers.
+  for (const auto *Init : Tmpl->inits()) {
+    // Only instantiate written initializers, let Sema re-construct implicit
+    // ones.
+    if (!Init->isWritten())
+      continue;
+
+    SourceLocation EllipsisLoc;
+
+    if (Init->isPackExpansion()) {
+      // This is a pack expansion. We should expand it now.
+      TypeLoc BaseTL = Init->getTypeSourceInfo()->getTypeLoc();
+      SmallVector<UnexpandedParameterPack, 4> Unexpanded;
+      collectUnexpandedParameterPacks(BaseTL, Unexpanded);
+      collectUnexpandedParameterPacks(Init->getInit(), Unexpanded);
+      bool ShouldExpand = false;
+      bool RetainExpansion = false;
+      Optional<unsigned> NumExpansions;
+      if (CheckParameterPacksForExpansion(Init->getEllipsisLoc(),
+                                          BaseTL.getSourceRange(),
+                                          Unexpanded,
+                                          TemplateArgs, ShouldExpand,
+                                          RetainExpansion,
+                                          NumExpansions)) {
+        AnyErrors = true;
+        New->setInvalidDecl();
+        continue;
+      }
+      assert(ShouldExpand && "Partial instantiation of base initializer?");
+
+      // Loop over all of the arguments in the argument pack(s),
+      for (unsigned I = 0; I != *NumExpansions; ++I) {
+        Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(*this, I);
+
+        // Instantiate the initializer.
+        ExprResult TempInit = SubstInitializer(Init->getInit(), TemplateArgs,
+                                               /*CXXDirectInit=*/true);
+        if (TempInit.isInvalid()) {
+          AnyErrors = true;
+          break;
+        }
+
+        // Instantiate the base type.
+        TypeSourceInfo *BaseTInfo = SubstType(Init->getTypeSourceInfo(),
+                                              TemplateArgs,
+                                              Init->getSourceLocation(),
+                                              New->getDeclName());
+        if (!BaseTInfo) {
+          AnyErrors = true;
+          break;
+        }
+
+        // Build the initializer.
+        MemInitResult NewInit = BuildBaseInitializer(BaseTInfo->getType(),
+                                                     BaseTInfo, TempInit.get(),
+                                                     New->getParent(),
+                                                     SourceLocation());
+        if (NewInit.isInvalid()) {
+          AnyErrors = true;
+          break;
+        }
+
+        NewInits.push_back(NewInit.get());
+      }
+
+      continue;
+    }
+
+    // Instantiate the initializer.
+    ExprResult TempInit = SubstInitializer(Init->getInit(), TemplateArgs,
+                                           /*CXXDirectInit=*/true);
+    if (TempInit.isInvalid()) {
+      AnyErrors = true;
+      continue;
+    }
+
+    MemInitResult NewInit;
+    if (Init->isDelegatingInitializer() || Init->isBaseInitializer()) {
+      TypeSourceInfo *TInfo = SubstType(Init->getTypeSourceInfo(),
+                                        TemplateArgs,
+                                        Init->getSourceLocation(),
+                                        New->getDeclName());
+      if (!TInfo) {
+        AnyErrors = true;
+        New->setInvalidDecl();
+        continue;
+      }
+
+      if (Init->isBaseInitializer())
+        NewInit = BuildBaseInitializer(TInfo->getType(), TInfo, TempInit.get(),
+                                       New->getParent(), EllipsisLoc);
+      else
+        NewInit = BuildDelegatingInitializer(TInfo, TempInit.get(),
+                                  cast<CXXRecordDecl>(CurContext->getParent()));
+    } else if (Init->isMemberInitializer()) {
+      FieldDecl *Member = cast_or_null<FieldDecl>(FindInstantiatedDecl(
+                                                     Init->getMemberLocation(),
+                                                     Init->getMember(),
+                                                     TemplateArgs));
+      if (!Member) {
+        AnyErrors = true;
+        New->setInvalidDecl();
+        continue;
+      }
+
+      NewInit = BuildMemberInitializer(Member, TempInit.get(),
+                                       Init->getSourceLocation());
+    } else if (Init->isIndirectMemberInitializer()) {
+      IndirectFieldDecl *IndirectMember =
+         cast_or_null<IndirectFieldDecl>(FindInstantiatedDecl(
+                                 Init->getMemberLocation(),
+                                 Init->getIndirectMember(), TemplateArgs));
+
+      if (!IndirectMember) {
+        AnyErrors = true;
+        New->setInvalidDecl();
+        continue;
+      }
+
+      NewInit = BuildMemberInitializer(IndirectMember, TempInit.get(),
+                                       Init->getSourceLocation());
+    }
+
+    if (NewInit.isInvalid()) {
+      AnyErrors = true;
+      New->setInvalidDecl();
+    } else {
+      NewInits.push_back(NewInit.get());
+    }
+  }
+
+  // Assign all the initializers to the new constructor.
+  ActOnMemInitializers(New,
+                       /*FIXME: ColonLoc */
+                       SourceLocation(),
+                       NewInits,
+                       AnyErrors);
+}
+
+// TODO: this could be templated if the various decl types used the
+// same method name.
+static bool isInstantiationOf(ClassTemplateDecl *Pattern,
+                              ClassTemplateDecl *Instance) {
+  Pattern = Pattern->getCanonicalDecl();
+
+  do {
+    Instance = Instance->getCanonicalDecl();
+    if (Pattern == Instance) return true;
+    Instance = Instance->getInstantiatedFromMemberTemplate();
+  } while (Instance);
+
+  return false;
+}
+
+static bool isInstantiationOf(FunctionTemplateDecl *Pattern,
+                              FunctionTemplateDecl *Instance) {
+  Pattern = Pattern->getCanonicalDecl();
+
+  do {
+    Instance = Instance->getCanonicalDecl();
+    if (Pattern == Instance) return true;
+    Instance = Instance->getInstantiatedFromMemberTemplate();
+  } while (Instance);
+
+  return false;
+}
+
+static bool
+isInstantiationOf(ClassTemplatePartialSpecializationDecl *Pattern,
+                  ClassTemplatePartialSpecializationDecl *Instance) {
+  Pattern
+    = cast<ClassTemplatePartialSpecializationDecl>(Pattern->getCanonicalDecl());
+  do {
+    Instance = cast<ClassTemplatePartialSpecializationDecl>(
+                                                Instance->getCanonicalDecl());
+    if (Pattern == Instance)
+      return true;
+    Instance = Instance->getInstantiatedFromMember();
+  } while (Instance);
+
+  return false;
+}
+
+static bool isInstantiationOf(CXXRecordDecl *Pattern,
+                              CXXRecordDecl *Instance) {
+  Pattern = Pattern->getCanonicalDecl();
+
+  do {
+    Instance = Instance->getCanonicalDecl();
+    if (Pattern == Instance) return true;
+    Instance = Instance->getInstantiatedFromMemberClass();
+  } while (Instance);
+
+  return false;
+}
+
+static bool isInstantiationOf(FunctionDecl *Pattern,
+                              FunctionDecl *Instance) {
+  Pattern = Pattern->getCanonicalDecl();
+
+  do {
+    Instance = Instance->getCanonicalDecl();
+    if (Pattern == Instance) return true;
+    Instance = Instance->getInstantiatedFromMemberFunction();
+  } while (Instance);
+
+  return false;
+}
+
+static bool isInstantiationOf(EnumDecl *Pattern,
+                              EnumDecl *Instance) {
+  Pattern = Pattern->getCanonicalDecl();
+
+  do {
+    Instance = Instance->getCanonicalDecl();
+    if (Pattern == Instance) return true;
+    Instance = Instance->getInstantiatedFromMemberEnum();
+  } while (Instance);
+
+  return false;
+}
+
+static bool isInstantiationOf(UsingShadowDecl *Pattern,
+                              UsingShadowDecl *Instance,
+                              ASTContext &C) {
+  return declaresSameEntity(C.getInstantiatedFromUsingShadowDecl(Instance),
+                            Pattern);
+}
+
+static bool isInstantiationOf(UsingDecl *Pattern, UsingDecl *Instance,
+                              ASTContext &C) {
+  return declaresSameEntity(C.getInstantiatedFromUsingDecl(Instance), Pattern);
+}
+
+template<typename T>
+static bool isInstantiationOfUnresolvedUsingDecl(T *Pattern, Decl *Other,
+                                                 ASTContext &Ctx) {
+  // An unresolved using declaration can instantiate to an unresolved using
+  // declaration, or to a using declaration or a using declaration pack.
+  //
+  // Multiple declarations can claim to be instantiated from an unresolved
+  // using declaration if it's a pack expansion. We want the UsingPackDecl
+  // in that case, not the individual UsingDecls within the pack.
+  bool OtherIsPackExpansion;
+  NamedDecl *OtherFrom;
+  if (auto *OtherUUD = dyn_cast<T>(Other)) {
+    OtherIsPackExpansion = OtherUUD->isPackExpansion();
+    OtherFrom = Ctx.getInstantiatedFromUsingDecl(OtherUUD);
+  } else if (auto *OtherUPD = dyn_cast<UsingPackDecl>(Other)) {
+    OtherIsPackExpansion = true;
+    OtherFrom = OtherUPD->getInstantiatedFromUsingDecl();
+  } else if (auto *OtherUD = dyn_cast<UsingDecl>(Other)) {
+    OtherIsPackExpansion = false;
+    OtherFrom = Ctx.getInstantiatedFromUsingDecl(OtherUD);
+  } else {
+    return false;
+  }
+  return Pattern->isPackExpansion() == OtherIsPackExpansion &&
+         declaresSameEntity(OtherFrom, Pattern);
+}
+
+static bool isInstantiationOfStaticDataMember(VarDecl *Pattern,
+                                              VarDecl *Instance) {
+  assert(Instance->isStaticDataMember());
+
+  Pattern = Pattern->getCanonicalDecl();
+
+  do {
+    Instance = Instance->getCanonicalDecl();
+    if (Pattern == Instance) return true;
+    Instance = Instance->getInstantiatedFromStaticDataMember();
+  } while (Instance);
+
+  return false;
+}
+
+// Other is the prospective instantiation
+// D is the prospective pattern
+static bool isInstantiationOf(ASTContext &Ctx, NamedDecl *D, Decl *Other) {
+  if (auto *UUD = dyn_cast<UnresolvedUsingTypenameDecl>(D))
+    return isInstantiationOfUnresolvedUsingDecl(UUD, Other, Ctx);
+
+  if (auto *UUD = dyn_cast<UnresolvedUsingValueDecl>(D))
+    return isInstantiationOfUnresolvedUsingDecl(UUD, Other, Ctx);
+
+  if (D->getKind() != Other->getKind())
+    return false;
+
+  if (auto *Record = dyn_cast<CXXRecordDecl>(Other))
+    return isInstantiationOf(cast<CXXRecordDecl>(D), Record);
+
+  if (auto *Function = dyn_cast<FunctionDecl>(Other))
+    return isInstantiationOf(cast<FunctionDecl>(D), Function);
+
+  if (auto *Enum = dyn_cast<EnumDecl>(Other))
+    return isInstantiationOf(cast<EnumDecl>(D), Enum);
+
+  if (auto *Var = dyn_cast<VarDecl>(Other))
+    if (Var->isStaticDataMember())
+      return isInstantiationOfStaticDataMember(cast<VarDecl>(D), Var);
+
+  if (auto *Temp = dyn_cast<ClassTemplateDecl>(Other))
+    return isInstantiationOf(cast<ClassTemplateDecl>(D), Temp);
+
+  if (auto *Temp = dyn_cast<FunctionTemplateDecl>(Other))
+    return isInstantiationOf(cast<FunctionTemplateDecl>(D), Temp);
+
+  if (auto *PartialSpec =
+          dyn_cast<ClassTemplatePartialSpecializationDecl>(Other))
+    return isInstantiationOf(cast<ClassTemplatePartialSpecializationDecl>(D),
+                             PartialSpec);
+
+  if (auto *Field = dyn_cast<FieldDecl>(Other)) {
+    if (!Field->getDeclName()) {
+      // This is an unnamed field.
+      return declaresSameEntity(Ctx.getInstantiatedFromUnnamedFieldDecl(Field),
+                                cast<FieldDecl>(D));
+    }
+  }
+
+  if (auto *Using = dyn_cast<UsingDecl>(Other))
+    return isInstantiationOf(cast<UsingDecl>(D), Using, Ctx);
+
+  if (auto *Shadow = dyn_cast<UsingShadowDecl>(Other))
+    return isInstantiationOf(cast<UsingShadowDecl>(D), Shadow, Ctx);
+
+  return D->getDeclName() &&
+         D->getDeclName() == cast<NamedDecl>(Other)->getDeclName();
+}
+
+template<typename ForwardIterator>
+static NamedDecl *findInstantiationOf(ASTContext &Ctx,
+                                      NamedDecl *D,
+                                      ForwardIterator first,
+                                      ForwardIterator last) {
+  for (; first != last; ++first)
+    if (isInstantiationOf(Ctx, D, *first))
+      return cast<NamedDecl>(*first);
+
+  return nullptr;
+}
+
+/// Finds the instantiation of the given declaration context
+/// within the current instantiation.
+///
+/// \returns NULL if there was an error
+DeclContext *Sema::FindInstantiatedContext(SourceLocation Loc, DeclContext* DC,
+                          const MultiLevelTemplateArgumentList &TemplateArgs) {
+  if (NamedDecl *D = dyn_cast<NamedDecl>(DC)) {
+    Decl* ID = FindInstantiatedDecl(Loc, D, TemplateArgs, true);
+    return cast_or_null<DeclContext>(ID);
+  } else return DC;
+}
+
+/// Find the instantiation of the given declaration within the
+/// current instantiation.
+///
+/// This routine is intended to be used when \p D is a declaration
+/// referenced from within a template, that needs to mapped into the
+/// corresponding declaration within an instantiation. For example,
+/// given:
+///
+/// \code
+/// template<typename T>
+/// struct X {
+///   enum Kind {
+///     KnownValue = sizeof(T)
+///   };
+///
+///   bool getKind() const { return KnownValue; }
+/// };
+///
+/// template struct X<int>;
+/// \endcode
+///
+/// In the instantiation of <tt>X<int>::getKind()</tt>, we need to map the
+/// \p EnumConstantDecl for \p KnownValue (which refers to
+/// <tt>X<T>::<Kind>::KnownValue</tt>) to its instantiation
+/// (<tt>X<int>::<Kind>::KnownValue</tt>). \p FindInstantiatedDecl performs
+/// this mapping from within the instantiation of <tt>X<int></tt>.
+NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
+                          const MultiLevelTemplateArgumentList &TemplateArgs,
+                          bool FindingInstantiatedContext) {
+  DeclContext *ParentDC = D->getDeclContext();
+  // FIXME: Parmeters of pointer to functions (y below) that are themselves
+  // parameters (p below) can have their ParentDC set to the translation-unit
+  // - thus we can not consistently check if the ParentDC of such a parameter
+  // is Dependent or/and a FunctionOrMethod.
+  // For e.g. this code, during Template argument deduction tries to
+  // find an instantiated decl for (T y) when the ParentDC for y is
+  // the translation unit.
+  //   e.g. template <class T> void Foo(auto (*p)(T y) -> decltype(y())) {}
+  //   float baz(float(*)()) { return 0.0; }
+  //   Foo(baz);
+  // The better fix here is perhaps to ensure that a ParmVarDecl, by the time
+  // it gets here, always has a FunctionOrMethod as its ParentDC??
+  // For now:
+  //  - as long as we have a ParmVarDecl whose parent is non-dependent and
+  //    whose type is not instantiation dependent, do nothing to the decl
+  //  - otherwise find its instantiated decl.
+  if (isa<ParmVarDecl>(D) && !ParentDC->isDependentContext() &&
+      !cast<ParmVarDecl>(D)->getType()->isInstantiationDependentType())
+    return D;
+  if (isa<ParmVarDecl>(D) || isa<NonTypeTemplateParmDecl>(D) ||
+      isa<TemplateTypeParmDecl>(D) || isa<TemplateTemplateParmDecl>(D) ||
+      ((ParentDC->isFunctionOrMethod() ||
+        isa<OMPDeclareReductionDecl>(ParentDC) ||
+        isa<OMPDeclareMapperDecl>(ParentDC)) &&
+       ParentDC->isDependentContext()) ||
+      (isa<CXXRecordDecl>(D) && cast<CXXRecordDecl>(D)->isLambda())) {
+    // D is a local of some kind. Look into the map of local
+    // declarations to their instantiations.
+    if (CurrentInstantiationScope) {
+      if (auto Found = CurrentInstantiationScope->findInstantiationOf(D)) {
+        if (Decl *FD = Found->dyn_cast<Decl *>())
+          return cast<NamedDecl>(FD);
+
+        int PackIdx = ArgumentPackSubstitutionIndex;
+        assert(PackIdx != -1 &&
+               "found declaration pack but not pack expanding");
+        typedef LocalInstantiationScope::DeclArgumentPack DeclArgumentPack;
+        return cast<NamedDecl>((*Found->get<DeclArgumentPack *>())[PackIdx]);
+      }
+    }
+
+    // If we're performing a partial substitution during template argument
+    // deduction, we may not have values for template parameters yet. They
+    // just map to themselves.
+    if (isa<NonTypeTemplateParmDecl>(D) || isa<TemplateTypeParmDecl>(D) ||
+        isa<TemplateTemplateParmDecl>(D))
+      return D;
+
+    if (D->isInvalidDecl())
+      return nullptr;
+
+    // Normally this function only searches for already instantiated declaration
+    // however we have to make an exclusion for local types used before
+    // definition as in the code:
+    //
+    //   template<typename T> void f1() {
+    //     void g1(struct x1);
+    //     struct x1 {};
+    //   }
+    //
+    // In this case instantiation of the type of 'g1' requires definition of
+    // 'x1', which is defined later. Error recovery may produce an enum used
+    // before definition. In these cases we need to instantiate relevant
+    // declarations here.
+    bool NeedInstantiate = false;
+    if (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D))
+      NeedInstantiate = RD->isLocalClass();
+    else
+      NeedInstantiate = isa<EnumDecl>(D);
+    if (NeedInstantiate) {
+      Decl *Inst = SubstDecl(D, CurContext, TemplateArgs);
+      CurrentInstantiationScope->InstantiatedLocal(D, Inst);
+      return cast<TypeDecl>(Inst);
+    }
+
+    // If we didn't find the decl, then we must have a label decl that hasn't
+    // been found yet.  Lazily instantiate it and return it now.
+    assert(isa<LabelDecl>(D));
+
+    Decl *Inst = SubstDecl(D, CurContext, TemplateArgs);
+    assert(Inst && "Failed to instantiate label??");
+
+    CurrentInstantiationScope->InstantiatedLocal(D, Inst);
+    return cast<LabelDecl>(Inst);
+  }
+
+  // For variable template specializations, update those that are still
+  // type-dependent.
+  if (VarTemplateSpecializationDecl *VarSpec =
+          dyn_cast<VarTemplateSpecializationDecl>(D)) {
+    bool InstantiationDependent = false;
+    const TemplateArgumentListInfo &VarTemplateArgs =
+        VarSpec->getTemplateArgsInfo();
+    if (TemplateSpecializationType::anyDependentTemplateArguments(
+            VarTemplateArgs, InstantiationDependent))
+      D = cast<NamedDecl>(
+          SubstDecl(D, VarSpec->getDeclContext(), TemplateArgs));
+    return D;
+  }
+
+  if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(D)) {
+    if (!Record->isDependentContext())
+      return D;
+
+    // Determine whether this record is the "templated" declaration describing
+    // a class template or class template partial specialization.
+    ClassTemplateDecl *ClassTemplate = Record->getDescribedClassTemplate();
+    if (ClassTemplate)
+      ClassTemplate = ClassTemplate->getCanonicalDecl();
+    else if (ClassTemplatePartialSpecializationDecl *PartialSpec
+               = dyn_cast<ClassTemplatePartialSpecializationDecl>(Record))
+      ClassTemplate = PartialSpec->getSpecializedTemplate()->getCanonicalDecl();
+
+    // Walk the current context to find either the record or an instantiation of
+    // it.
+    DeclContext *DC = CurContext;
+    while (!DC->isFileContext()) {
+      // If we're performing substitution while we're inside the template
+      // definition, we'll find our own context. We're done.
+      if (DC->Equals(Record))
+        return Record;
+
+      if (CXXRecordDecl *InstRecord = dyn_cast<CXXRecordDecl>(DC)) {
+        // Check whether we're in the process of instantiating a class template
+        // specialization of the template we're mapping.
+        if (ClassTemplateSpecializationDecl *InstSpec
+                      = dyn_cast<ClassTemplateSpecializationDecl>(InstRecord)){
+          ClassTemplateDecl *SpecTemplate = InstSpec->getSpecializedTemplate();
+          if (ClassTemplate && isInstantiationOf(ClassTemplate, SpecTemplate))
+            return InstRecord;
+        }
+
+        // Check whether we're in the process of instantiating a member class.
+        if (isInstantiationOf(Record, InstRecord))
+          return InstRecord;
+      }
+
+      // Move to the outer template scope.
+      if (FunctionDecl *FD = dyn_cast<FunctionDecl>(DC)) {
+        if (FD->getFriendObjectKind() && FD->getDeclContext()->isFileContext()){
+          DC = FD->getLexicalDeclContext();
+          continue;
+        }
+        // An implicit deduction guide acts as if it's within the class template
+        // specialization described by its name and first N template params.
+        auto *Guide = dyn_cast<CXXDeductionGuideDecl>(FD);
+        if (Guide && Guide->isImplicit()) {
+          TemplateDecl *TD = Guide->getDeducedTemplate();
+          // Convert the arguments to an "as-written" list.
+          TemplateArgumentListInfo Args(Loc, Loc);
+          for (TemplateArgument Arg : TemplateArgs.getInnermost().take_front(
+                                        TD->getTemplateParameters()->size())) {
+            ArrayRef<TemplateArgument> Unpacked(Arg);
+            if (Arg.getKind() == TemplateArgument::Pack)
+              Unpacked = Arg.pack_elements();
+            for (TemplateArgument UnpackedArg : Unpacked)
+              Args.addArgument(
+                  getTrivialTemplateArgumentLoc(UnpackedArg, QualType(), Loc));
+          }
+          QualType T = CheckTemplateIdType(TemplateName(TD), Loc, Args);
+          if (T.isNull())
+            return nullptr;
+          auto *SubstRecord = T->getAsCXXRecordDecl();
+          assert(SubstRecord && "class template id not a class type?");
+          // Check that this template-id names the primary template and not a
+          // partial or explicit specialization. (In the latter cases, it's
+          // meaningless to attempt to find an instantiation of D within the
+          // specialization.)
+          // FIXME: The standard doesn't say what should happen here.
+          if (FindingInstantiatedContext &&
+              usesPartialOrExplicitSpecialization(
+                  Loc, cast<ClassTemplateSpecializationDecl>(SubstRecord))) {
+            Diag(Loc, diag::err_specialization_not_primary_template)
+              << T << (SubstRecord->getTemplateSpecializationKind() ==
+                           TSK_ExplicitSpecialization);
+            return nullptr;
+          }
+          DC = SubstRecord;
+          continue;
+        }
+      }
+
+      DC = DC->getParent();
+    }
+
+    // Fall through to deal with other dependent record types (e.g.,
+    // anonymous unions in class templates).
+  }
+
+  if (!ParentDC->isDependentContext())
+    return D;
+
+  ParentDC = FindInstantiatedContext(Loc, ParentDC, TemplateArgs);
+  if (!ParentDC)
+    return nullptr;
+
+  if (ParentDC != D->getDeclContext()) {
+    // We performed some kind of instantiation in the parent context,
+    // so now we need to look into the instantiated parent context to
+    // find the instantiation of the declaration D.
+
+    // If our context used to be dependent, we may need to instantiate
+    // it before performing lookup into that context.
+    bool IsBeingInstantiated = false;
+    if (CXXRecordDecl *Spec = dyn_cast<CXXRecordDecl>(ParentDC)) {
+      if (!Spec->isDependentContext()) {
+        QualType T = Context.getTypeDeclType(Spec);
+        const RecordType *Tag = T->getAs<RecordType>();
+        assert(Tag && "type of non-dependent record is not a RecordType");
+        if (Tag->isBeingDefined())
+          IsBeingInstantiated = true;
+        if (!Tag->isBeingDefined() &&
+            RequireCompleteType(Loc, T, diag::err_incomplete_type))
+          return nullptr;
+
+        ParentDC = Tag->getDecl();
+      }
+    }
+
+    NamedDecl *Result = nullptr;
+    // FIXME: If the name is a dependent name, this lookup won't necessarily
+    // find it. Does that ever matter?
+    if (auto Name = D->getDeclName()) {
+      DeclarationNameInfo NameInfo(Name, D->getLocation());
+      Name = SubstDeclarationNameInfo(NameInfo, TemplateArgs).getName();
+      if (!Name)
+        return nullptr;
+      DeclContext::lookup_result Found = ParentDC->lookup(Name);
+      Result = findInstantiationOf(Context, D, Found.begin(), Found.end());
+    } else {
+      // Since we don't have a name for the entity we're looking for,
+      // our only option is to walk through all of the declarations to
+      // find that name. This will occur in a few cases:
+      //
+      //   - anonymous struct/union within a template
+      //   - unnamed class/struct/union/enum within a template
+      //
+      // FIXME: Find a better way to find these instantiations!
+      Result = findInstantiationOf(Context, D,
+                                   ParentDC->decls_begin(),
+                                   ParentDC->decls_end());
+    }
+
+    if (!Result) {
+      if (isa<UsingShadowDecl>(D)) {
+        // UsingShadowDecls can instantiate to nothing because of using hiding.
+      } else if (Diags.hasErrorOccurred()) {
+        // We've already complained about something, so most likely this
+        // declaration failed to instantiate. There's no point in complaining
+        // further, since this is normal in invalid code.
+      } else if (IsBeingInstantiated) {
+        // The class in which this member exists is currently being
+        // instantiated, and we haven't gotten around to instantiating this
+        // member yet. This can happen when the code uses forward declarations
+        // of member classes, and introduces ordering dependencies via
+        // template instantiation.
+        Diag(Loc, diag::err_member_not_yet_instantiated)
+          << D->getDeclName()
+          << Context.getTypeDeclType(cast<CXXRecordDecl>(ParentDC));
+        Diag(D->getLocation(), diag::note_non_instantiated_member_here);
+      } else if (EnumConstantDecl *ED = dyn_cast<EnumConstantDecl>(D)) {
+        // This enumeration constant was found when the template was defined,
+        // but can't be found in the instantiation. This can happen if an
+        // unscoped enumeration member is explicitly specialized.
+        EnumDecl *Enum = cast<EnumDecl>(ED->getLexicalDeclContext());
+        EnumDecl *Spec = cast<EnumDecl>(FindInstantiatedDecl(Loc, Enum,
+                                                             TemplateArgs));
+        assert(Spec->getTemplateSpecializationKind() ==
+                 TSK_ExplicitSpecialization);
+        Diag(Loc, diag::err_enumerator_does_not_exist)
+          << D->getDeclName()
+          << Context.getTypeDeclType(cast<TypeDecl>(Spec->getDeclContext()));
+        Diag(Spec->getLocation(), diag::note_enum_specialized_here)
+          << Context.getTypeDeclType(Spec);
+      } else {
+        // We should have found something, but didn't.
+        llvm_unreachable("Unable to find instantiation of declaration!");
+      }
+    }
+
+    D = Result;
+  }
+
+  return D;
+}
+
+/// Performs template instantiation for all implicit template
+/// instantiations we have seen until this point.
+void Sema::PerformPendingInstantiations(bool LocalOnly) {
+  while (!PendingLocalImplicitInstantiations.empty() ||
+         (!LocalOnly && !PendingInstantiations.empty())) {
+    PendingImplicitInstantiation Inst;
+
+    if (PendingLocalImplicitInstantiations.empty()) {
+      Inst = PendingInstantiations.front();
+      PendingInstantiations.pop_front();
+    } else {
+      Inst = PendingLocalImplicitInstantiations.front();
+      PendingLocalImplicitInstantiations.pop_front();
+    }
+
+    // Instantiate function definitions
+    if (FunctionDecl *Function = dyn_cast<FunctionDecl>(Inst.first)) {
+      bool DefinitionRequired = Function->getTemplateSpecializationKind() ==
+                                TSK_ExplicitInstantiationDefinition;
+      if (Function->isMultiVersion()) {
+        getASTContext().forEachMultiversionedFunctionVersion(
+            Function, [this, Inst, DefinitionRequired](FunctionDecl *CurFD) {
+              InstantiateFunctionDefinition(/*FIXME:*/ Inst.second, CurFD, true,
+                                            DefinitionRequired, true);
+              if (CurFD->isDefined())
+                CurFD->setInstantiationIsPending(false);
+            });
+      } else {
+        InstantiateFunctionDefinition(/*FIXME:*/ Inst.second, Function, true,
+                                      DefinitionRequired, true);
+        if (Function->isDefined())
+          Function->setInstantiationIsPending(false);
+      }
+      continue;
+    }
+
+    // Instantiate variable definitions
+    VarDecl *Var = cast<VarDecl>(Inst.first);
+
+    assert((Var->isStaticDataMember() ||
+            isa<VarTemplateSpecializationDecl>(Var)) &&
+           "Not a static data member, nor a variable template"
+           " specialization?");
+
+    // Don't try to instantiate declarations if the most recent redeclaration
+    // is invalid.
+    if (Var->getMostRecentDecl()->isInvalidDecl())
+      continue;
+
+    // Check if the most recent declaration has changed the specialization kind
+    // and removed the need for implicit instantiation.
+    switch (Var->getMostRecentDecl()
+                ->getTemplateSpecializationKindForInstantiation()) {
+    case TSK_Undeclared:
+      llvm_unreachable("Cannot instantitiate an undeclared specialization.");
+    case TSK_ExplicitInstantiationDeclaration:
+    case TSK_ExplicitSpecialization:
+      continue;  // No longer need to instantiate this type.
+    case TSK_ExplicitInstantiationDefinition:
+      // We only need an instantiation if the pending instantiation *is* the
+      // explicit instantiation.
+      if (Var != Var->getMostRecentDecl())
+        continue;
+      break;
+    case TSK_ImplicitInstantiation:
+      break;
+    }
+
+    PrettyDeclStackTraceEntry CrashInfo(Context, Var, SourceLocation(),
+                                        "instantiating variable definition");
+    bool DefinitionRequired = Var->getTemplateSpecializationKind() ==
+                              TSK_ExplicitInstantiationDefinition;
+
+    // Instantiate static data member definitions or variable template
+    // specializations.
+    InstantiateVariableDefinition(/*FIXME:*/ Inst.second, Var, true,
+                                  DefinitionRequired, true);
+  }
+}
+
+void Sema::PerformDependentDiagnostics(const DeclContext *Pattern,
+                       const MultiLevelTemplateArgumentList &TemplateArgs) {
+  for (auto DD : Pattern->ddiags()) {
+    switch (DD->getKind()) {
+    case DependentDiagnostic::Access:
+      HandleDependentAccessCheck(*DD, TemplateArgs);
+      break;
+    }
+  }
+}