[llvm] [InstCombine] Explicitly match poison operand. NFCI (PR #141744)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Luke Lau (lukel97)

<details>
<summary>Changes</summary>

This is a follow up from https://github.com/llvm/llvm-project/pull/141300#discussion_r2109109224

An undef mask element in a shufflevector is really poison, so explicitly match it here for clarity.


---
Full diff: https://github.com/llvm/llvm-project/pull/141744.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp (+2-2) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index e01dafd36d30d..e101edf4a6208 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1422,7 +1422,7 @@ InstCombinerImpl::foldShuffledIntrinsicOperands(IntrinsicInst *II) {
   ArrayRef<int> Mask;
   auto *NonConstArg = find_if_not(II->args(), IsaPred<Constant>);
   if (!NonConstArg ||
-      !match(NonConstArg, m_Shuffle(m_Value(X), m_Undef(), m_Mask(Mask))))
+      !match(NonConstArg, m_Shuffle(m_Value(X), m_Poison(), m_Mask(Mask))))
     return nullptr;
 
   // At least 1 operand must have 1 use because we are creating 2 instructions.
@@ -1433,7 +1433,7 @@ InstCombinerImpl::foldShuffledIntrinsicOperands(IntrinsicInst *II) {
   SmallVector<Value *, 4> NewArgs;
   Type *SrcTy = X->getType();
   for (Value *Arg : II->args()) {
-    if (match(Arg, m_Shuffle(m_Value(X), m_Undef(), m_SpecificMask(Mask))) &&
+    if (match(Arg, m_Shuffle(m_Value(X), m_Poison(), m_SpecificMask(Mask))) &&
         X->getType() == SrcTy)
       NewArgs.push_back(X);
     else if (match(Arg, m_ImmConstant(C))) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/141744