[CallPromotionUtils] Add tryPromoteCall.

[hjyamauchi]

Summary

It attempts to devirtualize a call on alloca through vtable loads.

[hjyamauchi]

This is split off of D69591.

[hjyamauchi]

Any comment?

[davidxl]

llvm/lib/Transforms/Utils/CallPromotionUtils.cpp

476

nit: VTableLoad --> VTablePointerLoad

489

VTable --> VTablePtr

508

Is this possible?

[hjyamauchi]

Address comments and rebase.

llvm/lib/Transforms/Utils/CallPromotionUtils.cpp

508

I think so. It's possible that some ill-formed vtable or the entry contains a null (function) pointer.

[hjyamauchi]

PTAL.

[davidxl]

lgtm

[hjyamauchi]

This depends on D71307 and wouldn't work without it. Can you take a look at that again?

[hjyamauchi]

Rebase past D71307.

[davidxl]

llvm/unittests/Transforms/Utils/CallPromotionUtilsTest.cpp

37

Can you also add a negative test case?

[hjyamauchi]

Address comment.

Add negative tests.

Also add a new test is derived from
clang/test/CodeGenCXX/member-function-pointer-calls.cpp which this change
combined with D69591 enables nice inlining/simplification.

[hjyamauchi]

PTAL.

[davidxl]

lgtm

llvm/include/llvm/Transforms/Utils/CallPromotionUtils.h

 /// This function creates an if-then-else structure at the location of the call
 /// site. The original call site is moved into the "else" block. A clone of the
 /// indirect call site is promoted, placed in the "then" block, and returned. If
 /// \p BranchWeights is non-null, it will be used to set !prof metadata on the
 /// new conditional branch.
 Instruction *promoteCallWithIfThenElse(CallSite CS, Function *Callee,
                                        MDNode *BranchWeights = nullptr);
 
+/// Try to promote (devirtualize) a virtual call on an Alloca. Return true on
+/// success.
+///
+/// Look for a pattern like:
+///
+///  %o = alloca %class.Impl
+///  %1 = getelementptr %class.Impl, %class.Impl* %o, i64 0, i32 0, i32 0
+///  store i32 (...)** bitcast (i8** getelementptr inbounds
+///      ({ [3 x i8*] }, { [3 x i8*] }* @_ZTV4Impl, i64 0, inrange i32 0, i64 2)
+///      to i32 (...)**), i32 (...)*** %1
+///  %2 = getelementptr inbounds %class.Impl, %class.Impl* %o, i64 0, i32 0
+///  %3 = bitcast %class.Interface* %2 to void (%class.Interface*)***
+///  %vtable.i = load void (%class.Interface*)**, void (%class.Interface*)*** %3
+///  %4 = load void (%class.Interface*)*, void (%class.Interface*)** %vtable.i
+///  call void %4(%class.Interface* nonnull %2)
+///
+/// @_ZTV4Impl = linkonce_odr dso_local unnamed_addr constant { [3 x i8*] }
+///     { [3 x i8*]
+///     [i8* null, i8* bitcast ({ i8*, i8*, i8* }* @_ZTI4Impl to i8*),
+///     i8* bitcast (void (%class.Impl*)* @_ZN4Impl3RunEv to i8*)] }
+///
+bool tryPromoteCall(CallSite &CS);
+
 } // end namespace llvm
 
 #endif // LLVM_TRANSFORMS_UTILS_CALLPROMOTIONUTILS_H

llvm/lib/Transforms/Utils/CallPromotionUtils.cpp

 //===- CallPromotionUtils.cpp - Utilities for call promotion ----*- 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
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements utilities useful for promoting indirect call sites to
 // direct call sites.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Utils/CallPromotionUtils.h"
+#include "llvm/Analysis/Loads.h"
+#include "llvm/Analysis/TypeMetadataUtils.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 
 using namespace llvm;
 
 #define DEBUG_TYPE "call-promotion-utils"
 
 /// Fix-up phi nodes in an invoke instruction's normal destination.
Instruction *llvm::promoteCallWithIfThenElse(CallSite CS, Function *Callee,
   // callee, 'NewInst' will be executed, otherwise the original call site will
   // be executed.
   Instruction *NewInst = versionCallSite(CS, Callee, BranchWeights);
 
   // Promote 'NewInst' so that it directly calls the desired function.
   return promoteCall(CallSite(NewInst), Callee);
 }
 
+bool llvm::tryPromoteCall(CallSite &CS) {
+  assert(!CS.getCalledFunction());
+  Module *M = CS.getCaller()->getParent();
+  const DataLayout &DL = M->getDataLayout();
+  Value *Callee = CS.getCalledValue();
+
+  LoadInst *VTableEntryLoad = dyn_cast<LoadInst>(Callee);
+  if (!VTableEntryLoad)
+    return false; // Not a vtable entry load.
+  Value *VTableEntryPtr = VTableEntryLoad->getPointerOperand();
+  APInt VTableOffset(DL.getTypeSizeInBits(VTableEntryPtr->getType()), 0);
+  Value *VTableBasePtr = VTableEntryPtr->stripAndAccumulateConstantOffsets(
+      DL, VTableOffset, /* AllowNonInbounds */ false);
+  LoadInst *VTableLoad = dyn_cast<LoadInst>(VTableBasePtr);
+  if (!VTableLoad)
+    return false; // Not a vtable load.
+  Value *Object = VTableLoad->getPointerOperand();
+  APInt ObjectOffset(DL.getTypeSizeInBits(Object->getType()), 0);
+  Value *ObjectBase = Object->stripAndAccumulateConstantOffsets(
+      DL, ObjectOffset, /* AllowNonInbounds */ false);
+  if (!(isa<AllocaInst>(ObjectBase) && ObjectOffset == 0))
+    // Not an Alloca or the offset isn't zero.
+    return false;
+
+  // Look for the vtable pointer store into the object by the ctor.
+  BasicBlock::iterator BBI(VTableLoad);
+  Value *VTable = FindAvailableLoadedValue(
+      VTableLoad, VTableLoad->getParent(), BBI, 0, nullptr, nullptr);
+  if (!VTable)
+    return false; // No vtable found.
+  APInt VTableOffsetGVBase(DL.getTypeSizeInBits(VTable->getType()), 0);
+  Value *VTableGVBase = VTable->stripAndAccumulateConstantOffsets(
+      DL, VTableOffsetGVBase, /* AllowNonInbounds */ false);
+  GlobalVariable *GV = dyn_cast<GlobalVariable>(VTableGVBase);
+  if (!(GV && GV->isConstant() && GV->hasDefinitiveInitializer()))
+    // Not in the form of a global constant variable with an initializer.
+    return false;
+
+  Constant *VTableGVInitializer = GV->getInitializer();
+  APInt VTableGVOffset = VTableOffsetGVBase + VTableOffset;
+  if (!(VTableGVOffset.getActiveBits() <= 64))
+    return false; // Out of range.
+  Constant *Ptr = getPointerAtOffset(VTableGVInitializer,
+                                     VTableGVOffset.getZExtValue(),
+                                     *M);
+  if (!Ptr)
+    return false; // No constant (function) pointer found.
+  Function *DirectCallee = dyn_cast<Function>(Ptr->stripPointerCasts());
+  if (!DirectCallee)
+    return false; // No function pointer found.
+
+  // Success.
+  promoteCall(CS, DirectCallee);
+  return true;
+}
+
 #undef DEBUG_TYPE

llvm/unittests/Transforms/Utils/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
   Analysis
   AsmParser
   Core
   Support
   TransformUtils
   )
 
 add_llvm_unittest(UtilsTests
   ASanStackFrameLayoutTest.cpp
   BasicBlockUtilsTest.cpp
+  CallPromotionUtilsTest.cpp
   CloningTest.cpp
   CodeExtractorTest.cpp
   CodeMoverUtilsTest.cpp
   FunctionComparatorTest.cpp
   IntegerDivisionTest.cpp
   LocalTest.cpp
   SizeOptsTest.cpp
   SSAUpdaterBulkTest.cpp
   UnrollLoopTest.cpp
   ValueMapperTest.cpp
   VFABIUtils.cpp
   )

llvm/unittests/Transforms/Utils/CallPromotionUtilsTest.cpp

+//===- CallPromotionUtilsTest.cpp - CallPromotionUtils unit tests ---------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/CallPromotionUtils.h"
+#include "llvm/AsmParser/Parser.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Support/SourceMgr.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+static std::unique_ptr<Module> parseIR(LLVMContext &C, const char *IR) {
+  SMDiagnostic Err;
+  std::unique_ptr<Module> Mod = parseAssemblyString(IR, Err, C);
+  if (!Mod)
+    Err.print("UtilsTests", errs());
+  return Mod;
+}
+
+TEST(CallPromotionUtilsTest, TryPromoteCall) {
+  LLVMContext C;
+  std::unique_ptr<Module> M = parseIR(C,
+                                      R"IR(
+%class.Impl = type <{ %class.Interface, i32, [4 x i8] }>
+%class.Interface = type { i32 (...)** }
+
+@_ZTV4Impl = constant { [3 x i8*] } { [3 x i8*] [i8* null, i8* null, i8* bitcast (void (%class.Impl*)* @_ZN4Impl3RunEv to i8*)] }
+
+define void @f() {
+entry:
+  %o = alloca %class.Impl
+  %base = getelementptr %class.Impl, %class.Impl* %o, i64 0, i32 0, i32 0
+  store i32 (...)** bitcast (i8** getelementptr inbounds ({ [3 x i8*] }, { [3 x i8*] }* @_ZTV4Impl, i64 0, inrange i32 0, i64 2) to i32 (...)**), i32 (...)*** %base
+  %f = getelementptr inbounds %class.Impl, %class.Impl* %o, i64 0, i32 1
+  store i32 3, i32* %f
+  %base.i = getelementptr inbounds %class.Impl, %class.Impl* %o, i64 0, i32 0
+  %c = bitcast %class.Interface* %base.i to void (%class.Interface*)***
+  %vtable.i = load void (%class.Interface*)**, void (%class.Interface*)*** %c
+  %fp = load void (%class.Interface*)*, void (%class.Interface*)** %vtable.i
+  call void %fp(%class.Interface* nonnull %base.i)
+  ret void
+}
+
+declare void @_ZN4Impl3RunEv(%class.Impl* %this)
+)IR");
+
+  auto *GV = M->getNamedValue("f");
+  ASSERT_TRUE(GV);
+  auto *F = dyn_cast<Function>(GV);
+  ASSERT_TRUE(F);
+  Instruction *Inst = &F->front().front();
+  auto *AI = dyn_cast<AllocaInst>(Inst);
+  ASSERT_TRUE(AI);
+  Inst = &*++F->front().rbegin();
+  auto *CI = dyn_cast<CallInst>(Inst);
+  ASSERT_TRUE(CI);
+  CallSite CS(CI);
+  ASSERT_FALSE(CS.getCalledFunction());
+  bool IsPromoted = tryPromoteCall(CS);
+  EXPECT_TRUE(IsPromoted);
+  GV = M->getNamedValue("_ZN4Impl3RunEv");
+  ASSERT_TRUE(GV);
+  auto *F1 = dyn_cast<Function>(GV);
+  EXPECT_EQ(F1, CS.getCalledFunction());
+}