Fold compares for distinct allocations
Summary:
We can fold compares to false when two distinct allocations within a
function are compared for equality.
Patch by Anna Thomas!
Reviewers: majnemer, reames, sanjoy
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D19390
llvm-svn: 267214
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index d8ff7f7..3ef9a9e 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1862,12 +1862,18 @@
return nullptr;
}
-static bool isNeverEqualToUnescapedAlloc(Value *V) {
+static bool isNeverEqualToUnescapedAlloc(Value *V, const TargetLibraryInfo *TLI,
+ Instruction *AI) {
if (isa<ConstantPointerNull>(V))
return true;
if (auto *LI = dyn_cast<LoadInst>(V))
return isa<GlobalVariable>(LI->getPointerOperand());
- return false;
+ // Two distinct allocations will never be equal.
+ // We rely on LookThroughBitCast in isAllocLikeFn being false, since looking
+ // through bitcasts of V can cause
+ // the result statement below to be true, even when AI and V (ex:
+ // i8* ->i32* ->i8* of AI) are the same allocations.
+ return isAllocLikeFn(V, TLI) && V != AI;
}
static bool
@@ -1894,12 +1900,12 @@
case Instruction::ICmp: {
ICmpInst *ICI = cast<ICmpInst>(I);
// We can fold eq/ne comparisons with null to false/true, respectively.
- // We fold comparisons in some conditions provided the alloc has not
- // escaped.
+ // We also fold comparisons in some conditions provided the alloc has
+ // not escaped.
if (!ICI->isEquality())
return false;
unsigned OtherIndex = (ICI->getOperand(0) == PI) ? 1 : 0;
- if (!isNeverEqualToUnescapedAlloc(ICI->getOperand(OtherIndex)))
+ if (!isNeverEqualToUnescapedAlloc(ICI->getOperand(OtherIndex), TLI, AI))
return false;
Users.emplace_back(I);
continue;