[VPlan] Fix MayReadFromMemory/MayWriteToMemory on VPWidenIntrinsicRecipe #136684
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These seem to be the wrong way round, e.g. see the definition at Instruction::mayReadFromMemory(). If an instruction only writes to memory then it's known to not read memory, and so on. Only noticed this when using VPWidenIntrinsicRecipe in a local patch and wondered why it kept on getting DCEd despite the intrinsic writing to memory.
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@llvm/pr-subscribers-vectorizers @llvm/pr-subscribers-llvm-transforms Author: Luke Lau (lukel97) ChangesThese seem to be the wrong way round, e.g. see the definition at Instruction::mayReadFromMemory(). Only noticed this when using VPWidenIntrinsicRecipe in a local patch and wondered why it kept on getting DCEd despite the intrinsic writing to memory. Full diff: https://github.com/llvm/llvm-project/pull/136684.diff 1 Files Affected:
diff --git a/llvm/lib/Transforms/Vectorize/VPlan.h b/llvm/lib/Transforms/Vectorize/VPlan.h
index 7084676af6d5b..1958502e5f8d3 100644
--- a/llvm/lib/Transforms/Vectorize/VPlan.h
+++ b/llvm/lib/Transforms/Vectorize/VPlan.h
@@ -1322,8 +1322,8 @@ class VPWidenIntrinsicRecipe : public VPRecipeWithIRFlags {
LLVMContext &Ctx = Ty->getContext();
AttributeSet Attrs = Intrinsic::getFnAttributes(Ctx, VectorIntrinsicID);
MemoryEffects ME = Attrs.getMemoryEffects();
- MayReadFromMemory = ME.onlyWritesMemory();
- MayWriteToMemory = ME.onlyReadsMemory();
+ MayReadFromMemory = !ME.onlyWritesMemory();
+ MayWriteToMemory = !ME.onlyReadsMemory();
MayHaveSideEffects = MayWriteToMemory ||
!Attrs.hasAttribute(Attribute::NoUnwind) ||
!Attrs.hasAttribute(Attribute::WillReturn);
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IanWood1
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May 6, 2025
…ipe (llvm#136684) These seem to be the wrong way round, e.g. see the definition at Instruction::mayReadFromMemory(). If an instruction only writes to memory then it's known to not read memory, and so on. Only noticed this when using VPWidenIntrinsicRecipe in a local patch and wondered why it kept on getting DCEd despite the intrinsic writing to memory.
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These seem to be the wrong way round, e.g. see the definition at Instruction::mayReadFromMemory().
If an instruction only writes to memory then it's known to not read memory, and so on.
Only noticed this when using VPWidenIntrinsicRecipe in a local patch and wondered why it kept on getting DCEd despite the intrinsic writing to memory.