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[VectorCombine] scalarizeLoadExtract - don't create scalar loads if any extract is waiting to be erased #129375

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Merged
merged 3 commits into from
Mar 1, 2025
Merged

[VectorCombine] scalarizeLoadExtract - don't create scalar loads if any extract is waiting to be erased #129375

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93eacbc
[VectorCombine] scalarizeLoadExtract - don't create scalar loads is a…
RKSimon Mar 1, 2025
ba9ba19
fix typo in test case name
RKSimon Mar 1, 2025
52a6511
Just use use_empty as we're only handling ExtractElementInst - isInst…
RKSimon Mar 1, 2025
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5 changes: 5 additions & 0 deletions llvm/lib/Transforms/Vectorize/VectorCombine.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1579,6 +1579,11 @@ bool VectorCombine::scalarizeLoadExtract(Instruction &I) {
if (!UI || UI->getParent() != LI->getParent())
return false;

// If any extract is waiting to be erased, then bail out as this will
// distort the cost calculation and possibly lead to infinite loops.
if (UI->use_empty())
return false;

// Check if any instruction between the load and the extract may modify
// memory.
if (LastCheckedInst->comesBefore(UI)) {
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12 changes: 12 additions & 0 deletions llvm/test/Transforms/VectorCombine/X86/load-extractelement-scalarization.ll
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Expand Up @@ -24,3 +24,15 @@ define void @multiple_extract(ptr %p) {
store i32 %e1, ptr %p1, align 4
ret void
}

; infinite loop if we fold an extract that is waiting to be erased
define void @unused_extract(ptr %p) {
; CHECK-LABEL: @unused_extract(
; CHECK-NEXT: ret void
;
%load = load <4 x float>, ptr %p, align 8
%shuffle0 = shufflevector <4 x float> zeroinitializer, <4 x float> %load, <4 x i32> <i32 0, i32 4, i32 1, i32 5>
%shuffle1 = shufflevector <4 x float> %shuffle0, <4 x float> zeroinitializer, <4 x i32> <i32 0, i32 4, i32 poison, i32 poison>
%extract = extractelement <4 x float> %load, i64 1
ret void
}