[llvm] [Hexagon] Change placeholder from `undef` to `poison` (PR #135555)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-hexagon

Author: Pedro Lobo (pedroclobo)

<details>
<summary>Changes</summary>

A `poison` vector should be used when performing an identity shuffle.

---
Full diff: https://github.com/llvm/llvm-project/pull/135555.diff


1 Files Affected:

- (modified) llvm/lib/Target/Hexagon/HexagonVectorCombine.cpp (+4-4) 


``````````diff
diff --git a/llvm/lib/Target/Hexagon/HexagonVectorCombine.cpp b/llvm/lib/Target/Hexagon/HexagonVectorCombine.cpp
index f800446592c06..d0f14d8ad7286 100644
--- a/llvm/lib/Target/Hexagon/HexagonVectorCombine.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonVectorCombine.cpp
@@ -2318,9 +2318,9 @@ auto HexagonVectorCombine::insertb(IRBuilderBase &Builder, Value *Dst,
   assert(0 <= Where && Where + Length <= DstLen);
 
   int P2Len = PowerOf2Ceil(SrcLen | DstLen);
-  auto *Undef = UndefValue::get(getByteTy());
-  Value *P2Src = vresize(Builder, Src, P2Len, Undef);
-  Value *P2Dst = vresize(Builder, Dst, P2Len, Undef);
+  auto *Poison = PoisonValue::get(getByteTy());
+  Value *P2Src = vresize(Builder, Src, P2Len, Poison);
+  Value *P2Dst = vresize(Builder, Dst, P2Len, Poison);
 
   SmallVector<int, 256> SMask(P2Len);
   for (int i = 0; i != P2Len; ++i) {
@@ -2331,7 +2331,7 @@ auto HexagonVectorCombine::insertb(IRBuilderBase &Builder, Value *Dst,
   }
 
   Value *P2Insert = Builder.CreateShuffleVector(P2Dst, P2Src, SMask, "shf");
-  return vresize(Builder, P2Insert, DstLen, Undef);
+  return vresize(Builder, P2Insert, DstLen, Poison);
 }
 
 auto HexagonVectorCombine::vlalignb(IRBuilderBase &Builder, Value *Lo,

``````````

</details>


https://github.com/llvm/llvm-project/pull/135555