1 files changed, 173 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/IPO/AlwaysInliner.cpp b/llvm/lib/Transforms/IPO/AlwaysInliner.cpp
new file mode 100644
index 000000000000..c50805692b98
--- /dev/null
+++ b/llvm/lib/Transforms/IPO/AlwaysInliner.cpp
@@ -0,0 +1,173 @@
+//===- InlineAlways.cpp - Code to inline always_inline functions ----------===//
+//
+// 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 a custom inliner that handles only functions that
+// are marked as "always inline".
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/IPO/AlwaysInliner.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/InlineCost.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/IR/CallSite.h"
+#include "llvm/IR/CallingConv.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Type.h"
+#include "llvm/Transforms/IPO.h"
+#include "llvm/Transforms/IPO/Inliner.h"
+#include "llvm/Transforms/Utils/Cloning.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "inline"
+
+PreservedAnalyses AlwaysInlinerPass::run(Module &M,
+                                         ModuleAnalysisManager &MAM) {
+  // Add inline assumptions during code generation.
+  FunctionAnalysisManager &FAM =
+      MAM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
+  std::function<AssumptionCache &(Function &)> GetAssumptionCache =
+      [&](Function &F) -> AssumptionCache & {
+    return FAM.getResult<AssumptionAnalysis>(F);
+  };
+  InlineFunctionInfo IFI(/*cg=*/nullptr, &GetAssumptionCache);
+
+  SmallSetVector<CallSite, 16> Calls;
+  bool Changed = false;
+  SmallVector<Function *, 16> InlinedFunctions;
+  for (Function &F : M)
+    if (!F.isDeclaration() && F.hasFnAttribute(Attribute::AlwaysInline) &&
+        isInlineViable(F)) {
+      Calls.clear();
+
+      for (User *U : F.users())
+        if (auto CS = CallSite(U))
+          if (CS.getCalledFunction() == &F)
+            Calls.insert(CS);
+
+      for (CallSite CS : Calls)
+        // FIXME: We really shouldn't be able to fail to inline at this point!
+        // We should do something to log or check the inline failures here.
+        Changed |=
+            InlineFunction(CS, IFI, /*CalleeAAR=*/nullptr, InsertLifetime);
+
+      // Remember to try and delete this function afterward. This both avoids
+      // re-walking the rest of the module and avoids dealing with any iterator
+      // invalidation issues while deleting functions.
+      InlinedFunctions.push_back(&F);
+    }
+
+  // Remove any live functions.
+  erase_if(InlinedFunctions, [&](Function *F) {
+    F->removeDeadConstantUsers();
+    return !F->isDefTriviallyDead();
+  });
+
+  // Delete the non-comdat ones from the module and also from our vector.
+  auto NonComdatBegin = partition(
+      InlinedFunctions, [&](Function *F) { return F->hasComdat(); });
+  for (Function *F : make_range(NonComdatBegin, InlinedFunctions.end()))
+    M.getFunctionList().erase(F);
+  InlinedFunctions.erase(NonComdatBegin, InlinedFunctions.end());
+
+  if (!InlinedFunctions.empty()) {
+    // Now we just have the comdat functions. Filter out the ones whose comdats
+    // are not actually dead.
+    filterDeadComdatFunctions(M, InlinedFunctions);
+    // The remaining functions are actually dead.
+    for (Function *F : InlinedFunctions)
+      M.getFunctionList().erase(F);
+  }
+
+  return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
+}
+
+namespace {
+
+/// Inliner pass which only handles "always inline" functions.
+///
+/// Unlike the \c AlwaysInlinerPass, this uses the more heavyweight \c Inliner
+/// base class to provide several facilities such as array alloca merging.
+class AlwaysInlinerLegacyPass : public LegacyInlinerBase {
+
+public:
+  AlwaysInlinerLegacyPass() : LegacyInlinerBase(ID, /*InsertLifetime*/ true) {
+    initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  AlwaysInlinerLegacyPass(bool InsertLifetime)
+      : LegacyInlinerBase(ID, InsertLifetime) {
+    initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  /// Main run interface method.  We override here to avoid calling skipSCC().
+  bool runOnSCC(CallGraphSCC &SCC) override { return inlineCalls(SCC); }
+
+  static char ID; // Pass identification, replacement for typeid
+
+  InlineCost getInlineCost(CallSite CS) override;
+
+  using llvm::Pass::doFinalization;
+  bool doFinalization(CallGraph &CG) override {
+    return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true);
+  }
+};
+}
+
+char AlwaysInlinerLegacyPass::ID = 0;
+INITIALIZE_PASS_BEGIN(AlwaysInlinerLegacyPass, "always-inline",
+                      "Inliner for always_inline functions", false, false)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_END(AlwaysInlinerLegacyPass, "always-inline",
+                    "Inliner for always_inline functions", false, false)
+
+Pass *llvm::createAlwaysInlinerLegacyPass(bool InsertLifetime) {
+  return new AlwaysInlinerLegacyPass(InsertLifetime);
+}
+
+/// Get the inline cost for the always-inliner.
+///
+/// The always inliner *only* handles functions which are marked with the
+/// attribute to force inlining. As such, it is dramatically simpler and avoids
+/// using the powerful (but expensive) inline cost analysis. Instead it uses
+/// a very simple and boring direct walk of the instructions looking for
+/// impossible-to-inline constructs.
+///
+/// Note, it would be possible to go to some lengths to cache the information
+/// computed here, but as we only expect to do this for relatively few and
+/// small functions which have the explicit attribute to force inlining, it is
+/// likely not worth it in practice.
+InlineCost AlwaysInlinerLegacyPass::getInlineCost(CallSite CS) {
+  Function *Callee = CS.getCalledFunction();
+
+  // Only inline direct calls to functions with always-inline attributes
+  // that are viable for inlining.
+  if (!Callee)
+    return InlineCost::getNever("indirect call");
+
+  // FIXME: We shouldn't even get here for declarations.
+  if (Callee->isDeclaration())
+    return InlineCost::getNever("no definition");
+
+  if (!CS.hasFnAttr(Attribute::AlwaysInline))
+    return InlineCost::getNever("no alwaysinline attribute");
+
+  auto IsViable = isInlineViable(*Callee);
+  if (!IsViable)
+    return InlineCost::getNever(IsViable.message);
+
+  return InlineCost::getAlways("always inliner");
+}