[VectorCombine] scalarizeLoadExtract - don't create scalar loads if any extract is waiting to be erased #129375
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…ny extract is waiting to be erased If any extract is waiting to be erased, then bail out as this will distort the cost calculation and possibly lead to infinite loops. Fixes llvm#129373
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@llvm/pr-subscribers-llvm-transforms Author: Simon Pilgrim (RKSimon) ChangesIf any extract is waiting to be erased, then bail out as this will distort the cost calculation and possibly lead to infinite loops. Fixes #129373 Full diff: https://github.com/llvm/llvm-project/pull/129375.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
index bb4e1c0f67e79..84cd08cd690d2 100644
--- a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
+++ b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -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 (isInstructionTriviallyDead(UI))
+ return false;
+
// Check if any instruction between the load and the extract may modify
// memory.
if (LastCheckedInst->comesBefore(UI)) {
diff --git a/llvm/test/Transforms/VectorCombine/X86/load-extractelement-scalarization.ll b/llvm/test/Transforms/VectorCombine/X86/load-extractelement-scalarization.ll
index 0acfeccb92ef7..4e95950591cbc 100644
--- a/llvm/test/Transforms/VectorCombine/X86/load-extractelement-scalarization.ll
+++ b/llvm/test/Transforms/VectorCombine/X86/load-extractelement-scalarization.ll
@@ -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 @unsued_extract(ptr %p) {
+; CHECK-LABEL: @unsued_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
+}
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@llvm/pr-subscribers-vectorizers Author: Simon Pilgrim (RKSimon) ChangesIf any extract is waiting to be erased, then bail out as this will distort the cost calculation and possibly lead to infinite loops. Fixes #129373 Full diff: https://github.com/llvm/llvm-project/pull/129375.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
index bb4e1c0f67e79..84cd08cd690d2 100644
--- a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
+++ b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -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 (isInstructionTriviallyDead(UI))
+ return false;
+
// Check if any instruction between the load and the extract may modify
// memory.
if (LastCheckedInst->comesBefore(UI)) {
diff --git a/llvm/test/Transforms/VectorCombine/X86/load-extractelement-scalarization.ll b/llvm/test/Transforms/VectorCombine/X86/load-extractelement-scalarization.ll
index 0acfeccb92ef7..4e95950591cbc 100644
--- a/llvm/test/Transforms/VectorCombine/X86/load-extractelement-scalarization.ll
+++ b/llvm/test/Transforms/VectorCombine/X86/load-extractelement-scalarization.ll
@@ -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 @unsued_extract(ptr %p) {
+; CHECK-LABEL: @unsued_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
+}
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dtcxzyw
approved these changes
Mar 1, 2025
llvm/test/Transforms/VectorCombine/X86/load-extractelement-scalarization.ll
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…ructionTriviallyDead is only needed for more complex general cases
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…ny extract is waiting to be erased (llvm#129375) If any extract is waiting to be erased, then bail out as this will distort the cost calculation and possibly lead to infinite loops. Fixes llvm#129373 (cherry picked from commit 5ddf40f)
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Mar 21, 2025
…ny extract is waiting to be erased (llvm#129375) If any extract is waiting to be erased, then bail out as this will distort the cost calculation and possibly lead to infinite loops. Fixes llvm#129373
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If any extract is waiting to be erased, then bail out as this will distort the cost calculation and possibly lead to infinite loops.
Fixes #129373