Folding compares with unescaped allocations
Summary:
If we know that the pointer allocated within a function does not escape,
we can fold away comparisons that are done with global pointers
Patch by Anna Thomas!
Reviewers: reames, majnemer, sanjoy
Subscribers: mgrang, mcrosier, majnemer, llvm-commits
Differential Revision: http://reviews.llvm.org/D19276
llvm-svn: 267035
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 8a9d282..586699d 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1863,6 +1863,14 @@
return nullptr;
}
+static bool isNeverEqualToUnescapedAlloc(Value *V) {
+ if (isa<ConstantPointerNull>(V))
+ return true;
+ if (auto *LI = dyn_cast<LoadInst>(V))
+ return isa<GlobalVariable>(LI->getPointerOperand());
+ return false;
+}
+
static bool
isAllocSiteRemovable(Instruction *AI, SmallVectorImpl<WeakVH> &Users,
const TargetLibraryInfo *TLI) {
@@ -1887,7 +1895,12 @@
case Instruction::ICmp: {
ICmpInst *ICI = cast<ICmpInst>(I);
// We can fold eq/ne comparisons with null to false/true, respectively.
- if (!ICI->isEquality() || !isa<ConstantPointerNull>(ICI->getOperand(1)))
+ // We 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)))
return false;
Users.emplace_back(I);
continue;