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[BasicAA][LAA] Don't use same-block phis in cross iteration mode #116802

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Merged
merged 1 commit into from
Nov 27, 2024
Merged

[BasicAA][LAA] Don't use same-block phis in cross iteration mode #116802

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5 changes: 3 additions & 2 deletions llvm/lib/Analysis/BasicAliasAnalysis.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1447,9 +1447,10 @@ AliasResult BasicAAResult::aliasPHI(const PHINode *PN, LocationSize PNSize,
return AliasResult::NoAlias;
// If the values are PHIs in the same block, we can do a more precise
// as well as efficient check: just check for aliases between the values
// on corresponding edges.
// on corresponding edges. Don't do this if we are analyzing across
// iterations, as we may pick a different phi entry in different iterations.
if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
if (PN2->getParent() == PN->getParent()) {
if (PN2->getParent() == PN->getParent() && !AAQI.MayBeCrossIteration) {
std::optional<AliasResult> Alias;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
AliasResult ThisAlias = AAQI.AAR.alias(
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7 changes: 6 additions & 1 deletion llvm/test/Analysis/LoopAccessAnalysis/select-dependence.ll
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Expand Up @@ -44,8 +44,13 @@ exit:
define void @test_phi(ptr noalias %x, ptr noalias %y, ptr noalias %z) {
; CHECK-LABEL: 'test_phi'
; CHECK-NEXT: loop:
; CHECK-NEXT: Memory dependences are safe
; CHECK-NEXT: Report: unsafe dependent memory operations in loop. Use #pragma clang loop distribute(enable) to allow loop distribution to attempt to isolate the offending operations into a separate loop
; CHECK-NEXT: Unsafe indirect dependence.
; CHECK-NEXT: Dependences:
; CHECK-NEXT: IndirectUnsafe:
; CHECK-NEXT: %load = load double, ptr %gep.sel, align 8 ->
; CHECK-NEXT: store double %load, ptr %gep.sel2, align 8
; CHECK-EMPTY:
; CHECK-NEXT: Run-time memory checks:
; CHECK-NEXT: Grouped accesses:
; CHECK-EMPTY:
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