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diff --git a/clang/lib/AST/Interp/ByteCodeExprGen.h b/clang/lib/AST/Interp/ByteCodeExprGen.h
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+++ b/clang/lib/AST/Interp/ByteCodeExprGen.h
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+//===--- ByteCodeExprGen.h - Code generator for expressions -----*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Defines the constexpr bytecode compiler.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_AST_INTERP_BYTECODEEXPRGEN_H
+#define LLVM_CLANG_AST_INTERP_BYTECODEEXPRGEN_H
+
+#include "ByteCodeEmitter.h"
+#include "EvalEmitter.h"
+#include "Pointer.h"
+#include "PrimType.h"
+#include "Record.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/Expr.h"
+#include "clang/AST/StmtVisitor.h"
+#include "llvm/ADT/Optional.h"
+
+namespace clang {
+class QualType;
+
+namespace interp {
+class Function;
+class State;
+
+template <class Emitter> class LocalScope;
+template <class Emitter> class RecordScope;
+template <class Emitter> class VariableScope;
+template <class Emitter> class DeclScope;
+template <class Emitter> class OptionScope;
+
+/// Compilation context for expressions.
+template <class Emitter>
+class ByteCodeExprGen : public ConstStmtVisitor<ByteCodeExprGen<Emitter>, bool>,
+                        public Emitter {
+protected:
+  // Emitters for opcodes of various arities.
+  using NullaryFn = bool (ByteCodeExprGen::*)(const SourceInfo &);
+  using UnaryFn = bool (ByteCodeExprGen::*)(PrimType, const SourceInfo &);
+  using BinaryFn = bool (ByteCodeExprGen::*)(PrimType, PrimType,
+                                             const SourceInfo &);
+
+  // Aliases for types defined in the emitter.
+  using LabelTy = typename Emitter::LabelTy;
+  using AddrTy = typename Emitter::AddrTy;
+
+  // Reference to a function generating the pointer of an initialized object.s
+  using InitFnRef = std::function<bool()>;
+
+  /// Current compilation context.
+  Context &Ctx;
+  /// Program to link to.
+  Program &P;
+
+public:
+  /// Initializes the compiler and the backend emitter.
+  template <typename... Tys>
+  ByteCodeExprGen(Context &Ctx, Program &P, Tys &&... Args)
+      : Emitter(Ctx, P, Args...), Ctx(Ctx), P(P) {}
+
+  // Expression visitors - result returned on stack.
+  bool VisitCastExpr(const CastExpr *E);
+  bool VisitIntegerLiteral(const IntegerLiteral *E);
+  bool VisitParenExpr(const ParenExpr *E);
+  bool VisitBinaryOperator(const BinaryOperator *E);
+
+protected:
+  bool visitExpr(const Expr *E) override;
+  bool visitDecl(const VarDecl *VD) override;
+
+protected:
+  /// Emits scope cleanup instructions.
+  void emitCleanup();
+
+  /// Returns a record type from a record or pointer type.
+  const RecordType *getRecordTy(QualType Ty);
+
+  /// Returns a record from a record or pointer type.
+  Record *getRecord(QualType Ty);
+  Record *getRecord(const RecordDecl *RD);
+
+  /// Returns the size int bits of an integer.
+  unsigned getIntWidth(QualType Ty) {
+    auto &ASTContext = Ctx.getASTContext();
+    return ASTContext.getIntWidth(Ty);
+  }
+
+  /// Returns the value of CHAR_BIT.
+  unsigned getCharBit() const {
+    auto &ASTContext = Ctx.getASTContext();
+    return ASTContext.getTargetInfo().getCharWidth();
+  }
+
+  /// Classifies a type.
+  llvm::Optional<PrimType> classify(const Expr *E) const {
+    return E->isGLValue() ? PT_Ptr : classify(E->getType());
+  }
+  llvm::Optional<PrimType> classify(QualType Ty) const {
+    return Ctx.classify(Ty);
+  }
+
+  /// Checks if a pointer needs adjustment.
+  bool needsAdjust(QualType Ty) const {
+    return true;
+  }
+
+  /// Classifies a known primitive type
+  PrimType classifyPrim(QualType Ty) const {
+    if (auto T = classify(Ty)) {
+      return *T;
+    }
+    llvm_unreachable("not a primitive type");
+  }
+
+  /// Evaluates an expression for side effects and discards the result.
+  bool discard(const Expr *E);
+  /// Evaluates an expression and places result on stack.
+  bool visit(const Expr *E);
+  /// Compiles an initializer for a local.
+  bool visitInitializer(const Expr *E, InitFnRef GenPtr);
+
+  /// Visits an expression and converts it to a boolean.
+  bool visitBool(const Expr *E);
+
+  /// Visits an initializer for a local.
+  bool visitLocalInitializer(const Expr *Init, unsigned I) {
+    return visitInitializer(Init, [this, I, Init] {
+      return this->emitGetPtrLocal(I, Init);
+    });
+  }
+
+  /// Visits an initializer for a global.
+  bool visitGlobalInitializer(const Expr *Init, unsigned I) {
+    return visitInitializer(Init, [this, I, Init] {
+      return this->emitGetPtrGlobal(I, Init);
+    });
+  }
+
+  /// Visits a delegated initializer.
+  bool visitThisInitializer(const Expr *I) {
+    return visitInitializer(I, [this, I] { return this->emitThis(I); });
+  }
+
+  /// Creates a local primitive value.
+  unsigned allocateLocalPrimitive(DeclTy &&Decl, PrimType Ty, bool IsMutable,
+                                  bool IsExtended = false);
+
+  /// Allocates a space storing a local given its type.
+  llvm::Optional<unsigned> allocateLocal(DeclTy &&Decl,
+                                         bool IsExtended = false);
+
+private:
+  friend class VariableScope<Emitter>;
+  friend class LocalScope<Emitter>;
+  friend class RecordScope<Emitter>;
+  friend class DeclScope<Emitter>;
+  friend class OptionScope<Emitter>;
+
+  /// Emits a zero initializer.
+  bool visitZeroInitializer(PrimType T, const Expr *E);
+
+  enum class DerefKind {
+    /// Value is read and pushed to stack.
+    Read,
+    /// Direct method generates a value which is written. Returns pointer.
+    Write,
+    /// Direct method receives the value, pushes mutated value. Returns pointer.
+    ReadWrite,
+  };
+
+  /// Method to directly load a value. If the value can be fetched directly,
+  /// the direct handler is called. Otherwise, a pointer is left on the stack
+  /// and the indirect handler is expected to operate on that.
+  bool dereference(const Expr *LV, DerefKind AK,
+                   llvm::function_ref<bool(PrimType)> Direct,
+                   llvm::function_ref<bool(PrimType)> Indirect);
+  bool dereferenceParam(const Expr *LV, PrimType T, const ParmVarDecl *PD,
+                        DerefKind AK,
+                        llvm::function_ref<bool(PrimType)> Direct,
+                        llvm::function_ref<bool(PrimType)> Indirect);
+  bool dereferenceVar(const Expr *LV, PrimType T, const VarDecl *PD,
+                      DerefKind AK, llvm::function_ref<bool(PrimType)> Direct,
+                      llvm::function_ref<bool(PrimType)> Indirect);
+
+  /// Emits an APInt constant.
+  bool emitConst(PrimType T, unsigned NumBits, const llvm::APInt &Value,
+                 const Expr *E);
+
+  /// Emits an integer constant.
+  template <typename T> bool emitConst(const Expr *E, T Value) {
+    QualType Ty = E->getType();
+    unsigned NumBits = getIntWidth(Ty);
+    APInt WrappedValue(NumBits, Value, std::is_signed<T>::value);
+    return emitConst(*Ctx.classify(Ty), NumBits, WrappedValue, E);
+  }
+
+  /// Returns a pointer to a variable declaration.
+  bool getPtrVarDecl(const VarDecl *VD, const Expr *E);
+
+  /// Returns the index of a global.
+  llvm::Optional<unsigned> getGlobalIdx(const VarDecl *VD);
+
+  /// Emits the initialized pointer.
+  bool emitInitFn() {
+    assert(InitFn && "missing initializer");
+    return (*InitFn)();
+  }
+
+protected:
+  /// Variable to storage mapping.
+  llvm::DenseMap<const ValueDecl *, Scope::Local> Locals;
+
+  /// OpaqueValueExpr to location mapping.
+  llvm::DenseMap<const OpaqueValueExpr *, unsigned> OpaqueExprs;
+
+  /// Current scope.
+  VariableScope<Emitter> *VarScope = nullptr;
+
+  /// Current argument index.
+  llvm::Optional<uint64_t> ArrayIndex;
+
+  /// Flag indicating if return value is to be discarded.
+  bool DiscardResult = false;
+
+  /// Expression being initialized.
+  llvm::Optional<InitFnRef> InitFn = {};
+};
+
+extern template class ByteCodeExprGen<ByteCodeEmitter>;
+extern template class ByteCodeExprGen<EvalEmitter>;
+
+/// Scope chain managing the variable lifetimes.
+template <class Emitter> class VariableScope {
+public:
+  virtual ~VariableScope() { Ctx->VarScope = this->Parent; }
+
+  void add(const Scope::Local &Local, bool IsExtended) {
+    if (IsExtended)
+      this->addExtended(Local);
+    else
+      this->addLocal(Local);
+  }
+
+  virtual void addLocal(const Scope::Local &Local) {
+    if (this->Parent)
+      this->Parent->addLocal(Local);
+  }
+
+  virtual void addExtended(const Scope::Local &Local) {
+    if (this->Parent)
+      this->Parent->addExtended(Local);
+  }
+
+  virtual void emitDestruction() {}
+
+  VariableScope *getParent() { return Parent; }
+
+protected:
+  VariableScope(ByteCodeExprGen<Emitter> *Ctx)
+      : Ctx(Ctx), Parent(Ctx->VarScope) {
+    Ctx->VarScope = this;
+  }
+
+  /// ByteCodeExprGen instance.
+  ByteCodeExprGen<Emitter> *Ctx;
+  /// Link to the parent scope.
+  VariableScope *Parent;
+};
+
+/// Scope for local variables.
+///
+/// When the scope is destroyed, instructions are emitted to tear down
+/// all variables declared in this scope.
+template <class Emitter> class LocalScope : public VariableScope<Emitter> {
+public:
+  LocalScope(ByteCodeExprGen<Emitter> *Ctx) : VariableScope<Emitter>(Ctx) {}
+
+  ~LocalScope() override { this->emitDestruction(); }
+
+  void addLocal(const Scope::Local &Local) override {
+    if (!Idx.hasValue()) {
+      Idx = this->Ctx->Descriptors.size();
+      this->Ctx->Descriptors.emplace_back();
+    }
+
+    this->Ctx->Descriptors[*Idx].emplace_back(Local);
+  }
+
+  void emitDestruction() override {
+    if (!Idx.hasValue())
+      return;
+    this->Ctx->emitDestroy(*Idx, SourceInfo{});
+  }
+
+protected:
+  /// Index of the scope in the chain.
+  Optional<unsigned> Idx;
+};
+
+/// Scope for storage declared in a compound statement.
+template <class Emitter> class BlockScope final : public LocalScope<Emitter> {
+public:
+  BlockScope(ByteCodeExprGen<Emitter> *Ctx) : LocalScope<Emitter>(Ctx) {}
+
+  void addExtended(const Scope::Local &Local) override {
+    llvm_unreachable("Cannot create temporaries in full scopes");
+  }
+};
+
+/// Expression scope which tracks potentially lifetime extended
+/// temporaries which are hoisted to the parent scope on exit.
+template <class Emitter> class ExprScope final : public LocalScope<Emitter> {
+public:
+  ExprScope(ByteCodeExprGen<Emitter> *Ctx) : LocalScope<Emitter>(Ctx) {}
+
+  void addExtended(const Scope::Local &Local) override {
+    this->Parent->addLocal(Local);
+  }
+};
+
+} // namespace interp
+} // namespace clang
+
+#endif