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[Mem2Reg] Don't use single store optimization for potentially poison value #97711

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Merged
merged 1 commit into from
Jul 4, 2024
Merged

[Mem2Reg] Don't use single store optimization for potentially poison value #97711

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10 changes: 8 additions & 2 deletions llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -525,7 +525,14 @@ rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info, LargeBlockInfo &LBI,
SmallSet<DbgAssignIntrinsic *, 8> *DbgAssignsToDelete,
SmallSet<DbgVariableRecord *, 8> *DVRAssignsToDelete) {
StoreInst *OnlyStore = Info.OnlyStore;
bool StoringGlobalVal = !isa<Instruction>(OnlyStore->getOperand(0));
Value *ReplVal = OnlyStore->getOperand(0);
// Loads may either load the stored value or uninitialized memory (undef).
// If the stored value may be poison, then replacing an uninitialized memory
// load with it would be incorrect.
if (!isGuaranteedNotToBePoison(ReplVal))
return false;

bool StoringGlobalVal = !isa<Instruction>(ReplVal);
BasicBlock *StoreBB = OnlyStore->getParent();
int StoreIndex = -1;

Expand Down Expand Up @@ -565,7 +572,6 @@ rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info, LargeBlockInfo &LBI,
}

// Otherwise, we *can* safely rewrite this load.
Value *ReplVal = OnlyStore->getOperand(0);
// If the replacement value is the load, this must occur in unreachable
// code.
if (ReplVal == LI)
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3 changes: 1 addition & 2 deletions llvm/test/Transforms/Mem2Reg/single-store.ll
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@@ -1,15 +1,14 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt -S -passes=mem2reg < %s | FileCheck %s

; FIXME: This is a miscompile.
define i8 @single_store_literal_poison(i1 %cond) {
; CHECK-LABEL: define i8 @single_store_literal_poison(
; CHECK-SAME: i1 [[COND:%.*]]) {
; CHECK-NEXT: br i1 [[COND]], label %[[IF:.*]], label %[[EXIT:.*]]
; CHECK: [[IF]]:
; CHECK-NEXT: br label %[[EXIT]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: ret i8 poison
; CHECK-NEXT: ret i8 undef
;
%a = alloca i8, align 1
br i1 %cond, label %if, label %exit
Expand Down