3 files changed, 79 insertions, 23 deletions

diff --git a/llvm/lib/Analysis/MemoryBuiltins.cpp b/llvm/lib/Analysis/MemoryBuiltins.cpp
index eaac506dec4..3e464f08f2e 100644
--- a/llvm/lib/Analysis/MemoryBuiltins.cpp
+++ b/llvm/lib/Analysis/MemoryBuiltins.cpp
@@ -109,25 +109,6 @@ static Optional<AllocFnsTy> getAllocationData(const Value *V, AllocType AllocTy,
   if (!Callee)
     return None;
 
-  // If it has allocsize, we can skip checking if it's a known function.
-  //
-  // MallocLike is chosen here because allocsize makes no guarantees about the
-  // nullness of the result of the function, nor does it deal with strings, nor
-  // does it require that the memory returned is zeroed out.
-  const AllocType AllocSizeAllocTy = MallocLike;
-  if ((AllocTy & AllocSizeAllocTy) == AllocSizeAllocTy &&
-      Callee->hasFnAttribute(Attribute::AllocSize)) {
-    Attribute Attr = Callee->getFnAttribute(Attribute::AllocSize);
-    std::pair<unsigned, Optional<unsigned>> Args = Attr.getAllocSizeArgs();
-
-    AllocFnsTy Result;
-    Result.AllocTy = AllocSizeAllocTy;
-    Result.NumParams = Callee->getNumOperands();
-    Result.FstParam = Args.first;
-    Result.SndParam = Args.second.getValueOr(-1);
-    return Result;
-  }
-
   // Make sure that the function is available.
   StringRef FnName = Callee->getName();
   LibFunc::Func TLIFn;
@@ -163,6 +144,32 @@ static Optional<AllocFnsTy> getAllocationData(const Value *V, AllocType AllocTy,
   return None;
 }
 
+static Optional<AllocFnsTy> getAllocationSize(const Value *V,
+                                              const TargetLibraryInfo *TLI) {
+  // Prefer to use existing information over allocsize. This will give us an
+  // accurate AllocTy.
+  if (Optional<AllocFnsTy> Data =
+          getAllocationData(V, AnyAlloc, TLI, /*LookThroughBitCast=*/false))
+    return Data;
+
+  // FIXME: Not calling getCalledFunction twice would be nice.
+  const Function *Callee = getCalledFunction(V, /*LookThroughBitCast=*/false);
+  if (!Callee || !Callee->hasFnAttribute(Attribute::AllocSize))
+    return None;
+
+  Attribute Attr = Callee->getFnAttribute(Attribute::AllocSize);
+  std::pair<unsigned, Optional<unsigned>> Args = Attr.getAllocSizeArgs();
+
+  AllocFnsTy Result;
+  // Because allocsize only tells us how many bytes are allocated, we're not
+  // really allowed to assume anything, so we use MallocLike.
+  Result.AllocTy = MallocLike;
+  Result.NumParams = Callee->getNumOperands();
+  Result.FstParam = Args.first;
+  Result.SndParam = Args.second.getValueOr(-1);
+  return Result;
+}
+
 static bool hasNoAliasAttr(const Value *V, bool LookThroughBitCast) {
   ImmutableCallSite CS(LookThroughBitCast ? V->stripPointerCasts() : V);
   return CS && CS.paramHasAttr(AttributeSet::ReturnIndex, Attribute::NoAlias);
@@ -505,8 +512,7 @@ SizeOffsetType ObjectSizeOffsetVisitor::visitArgument(Argument &A) {
 }
 
 SizeOffsetType ObjectSizeOffsetVisitor::visitCallSite(CallSite CS) {
-  Optional<AllocFnsTy> FnData =
-      getAllocationData(CS.getInstruction(), AnyAlloc, TLI);
+  Optional<AllocFnsTy> FnData = getAllocationSize(CS.getInstruction(), TLI);
   if (!FnData)
     return unknown();
 
@@ -765,8 +771,7 @@ SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitAllocaInst(AllocaInst &I) {
 }
 
 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitCallSite(CallSite CS) {
-  Optional<AllocFnsTy> FnData =
-      getAllocationData(CS.getInstruction(), AnyAlloc, TLI);
+  Optional<AllocFnsTy> FnData = getAllocationSize(CS.getInstruction(), TLI);
   if (!FnData)
     return unknown();
 
diff --git a/llvm/unittests/Analysis/CMakeLists.txt b/llvm/unittests/Analysis/CMakeLists.txt
index 33fc5c78ce5..65a2ac094cf 100644
--- a/llvm/unittests/Analysis/CMakeLists.txt
+++ b/llvm/unittests/Analysis/CMakeLists.txt
@@ -14,6 +14,7 @@ add_llvm_unittest(AnalysisTests
   CGSCCPassManagerTest.cpp
   LazyCallGraphTest.cpp
   LoopPassManagerTest.cpp
+  MemoryBuiltinsTest.cpp
   ScalarEvolutionTest.cpp
   TBAATest.cpp
   ValueTrackingTest.cpp
diff --git a/llvm/unittests/Analysis/MemoryBuiltinsTest.cpp b/llvm/unittests/Analysis/MemoryBuiltinsTest.cpp
new file mode 100644
index 00000000000..898ebeece4f
--- /dev/null
+++ b/llvm/unittests/Analysis/MemoryBuiltinsTest.cpp
@@ -0,0 +1,50 @@
+//===- MemoryBuiltinsTest.cpp - Tests for utilities in MemoryBuiltins.h ---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+// allocsize should not imply that a function is a traditional allocation
+// function (e.g. that can be optimized out/...); it just tells us how many
+// bytes exist at the pointer handed back by the function.
+TEST(AllocSize, AllocationBuiltinsTest) {
+  LLVMContext Context;
+  Module M("", Context);
+  IntegerType *ArgTy = Type::getInt32Ty(Context);
+
+  Function *AllocSizeFn = Function::Create(
+      FunctionType::get(Type::getInt8PtrTy(Context), {ArgTy}, false),
+      GlobalValue::ExternalLinkage, "F", &M);
+
+  AllocSizeFn->addFnAttr(Attribute::getWithAllocSizeArgs(Context, 1, None));
+
+  // 100 is arbitrary.
+  std::unique_ptr<CallInst> Caller(
+      CallInst::Create(AllocSizeFn, {ConstantInt::get(ArgTy, 100)}));
+
+  const TargetLibraryInfo *TLI = nullptr;
+  EXPECT_FALSE(isNoAliasFn(Caller.get(), TLI));
+  EXPECT_FALSE(isMallocLikeFn(Caller.get(), TLI));
+  EXPECT_FALSE(isCallocLikeFn(Caller.get(), TLI));
+  EXPECT_FALSE(isAllocLikeFn(Caller.get(), TLI));
+
+  // FIXME: We might be able to treat allocsize functions as general allocation
+  // functions. For the moment, being conservative seems better (and we'd have
+  // to plumb stuff around `isNoAliasFn`).
+  EXPECT_FALSE(isAllocationFn(Caller.get(), TLI));
+}
+}