[VPlan] Fix MayReadFromMemory/MayWriteToMemory on VPWidenIntrinsicRecipe

[lukel97]

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.

[llvmbot]

@llvm/pr-subscribers-vectorizers

@llvm/pr-subscribers-llvm-transforms

Author: Luke Lau (lukel97)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/136684.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/Vectorize/VPlan.h (+2-2)

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);

[fhahn]

LGTM, thanks