[llvm] [IR] Fix UB on Op<2> in ShuffleVector predicates (PR #75549)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-ir

Author: Reid Kleckner (rnk)

<details>
<summary>Changes</summary>

This Op<2> usage was missed in 1ee6ec2bf3, which replaced the third shuffle operand with a vector of integer mask constants.

I noticed this when attempting to make changes to the layout of llvm::Value.

---
Full diff: https://github.com/llvm/llvm-project/pull/75549.diff


1 Files Affected:

- (modified) llvm/lib/IR/Instructions.cpp (+1-8) 


``````````diff
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index bc228a577c6a6c..299b4e74677dcc 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -2412,9 +2412,6 @@ bool ShuffleVectorInst::isInsertSubvectorMask(ArrayRef<int> Mask,
 }
 
 bool ShuffleVectorInst::isIdentityWithPadding() const {
-  if (isa<UndefValue>(Op<2>()))
-    return false;
-
   // FIXME: Not currently possible to express a shuffle mask for a scalable
   // vector for this case.
   if (isa<ScalableVectorType>(getType()))
@@ -2439,9 +2436,6 @@ bool ShuffleVectorInst::isIdentityWithPadding() const {
 }
 
 bool ShuffleVectorInst::isIdentityWithExtract() const {
-  if (isa<UndefValue>(Op<2>()))
-    return false;
-
   // FIXME: Not currently possible to express a shuffle mask for a scalable
   // vector for this case.
   if (isa<ScalableVectorType>(getType()))
@@ -2457,8 +2451,7 @@ bool ShuffleVectorInst::isIdentityWithExtract() const {
 
 bool ShuffleVectorInst::isConcat() const {
   // Vector concatenation is differentiated from identity with padding.
-  if (isa<UndefValue>(Op<0>()) || isa<UndefValue>(Op<1>()) ||
-      isa<UndefValue>(Op<2>()))
+  if (isa<UndefValue>(Op<0>()) || isa<UndefValue>(Op<1>()))
     return false;
 
   // FIXME: Not currently possible to express a shuffle mask for a scalable

``````````

</details>


https://github.com/llvm/llvm-project/pull/75549