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[DSE] Use alias analysis to identify no-op stores #122610

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[DSE] Use alias analysis to identify no-op stores #122610

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4 changes: 3 additions & 1 deletion llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2116,7 +2116,9 @@ struct DSEState {
return true;

if (auto *LoadI = dyn_cast<LoadInst>(Store->getOperand(0))) {
if (LoadI->getPointerOperand() == Store->getOperand(1)) {
if (LoadI->getPointerOperand() == Store->getOperand(1) ||
AA.isMustAlias(MemoryLocation::get(LoadI),
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@justinfargnoli justinfargnoli Jan 13, 2025

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Confirming my understanding of the problem: checking that the address spaces are not equal is insufficient because address spaces may not be disjoint, correct?

MemoryLocation::get(Store))) {
// Get the defining access for the load.
auto *LoadAccess = MSSA.getMemoryAccess(LoadI)->getDefiningAccess();
// Fast path: the defining accesses are the same.
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11 changes: 11 additions & 0 deletions llvm/test/Transforms/DeadStoreElimination/noop-stores.ll
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Expand Up @@ -1152,3 +1152,14 @@ if.else:
end:
ret void
}

define i32 @test_use_alias_analysis(ptr %Q) {
; CHECK-LABEL: @test_use_alias_analysis(
; CHECK-NEXT: [[A:%.*]] = load i32, ptr [[Q:%.*]], align 4
; CHECK-NEXT: ret i32 [[A]]
;
%a = load i32, ptr %Q
%Q2 = addrspacecast ptr %Q to ptr addrspace(5)
store i32 %a, ptr addrspace(5) %Q2
ret i32 %a
}
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