[llvm] [DirectX] Change placeholders from `undef` to `poison` (PR #130970)

[Pedro Lobo via llvm-commits]

https://github.com/pedroclobo created https://github.com/llvm/llvm-project/pull/130970

Call `insertelement` with a `poison` vector.

>From 2dd292d248d2699372a3efeada092500b5b5460e Mon Sep 17 00:00:00 2001
From: Pedro Lobo <pedro.lobo at tecnico.ulisboa.pt>
Date: Tue, 11 Mar 2025 22:54:55 +0000
Subject: [PATCH] [DirectX] Change placeholders from `undef` to `poison`

Call `insertelement` with a `poison` vector.
---
 llvm/lib/Target/DirectX/DXILIntrinsicExpansion.cpp | 2 +-
 llvm/lib/Target/DirectX/DXILOpLowering.cpp         | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Target/DirectX/DXILIntrinsicExpansion.cpp b/llvm/lib/Target/DirectX/DXILIntrinsicExpansion.cpp
index cf142806bb1df..e44d3b70eb657 100644
--- a/llvm/lib/Target/DirectX/DXILIntrinsicExpansion.cpp
+++ b/llvm/lib/Target/DirectX/DXILIntrinsicExpansion.cpp
@@ -147,7 +147,7 @@ static Value *expandCrossIntrinsic(CallInst *Orig) {
   Value *zx_xz = MulSub(op0_z, op0_x, op1_z, op1_x);
   Value *xy_yx = MulSub(op0_x, op0_y, op1_x, op1_y);
 
-  Value *cross = UndefValue::get(VT);
+  Value *cross = PoisonValue::get(VT);
   cross = Builder.CreateInsertElement(cross, yz_zy, (uint64_t)0);
   cross = Builder.CreateInsertElement(cross, zx_xz, 1);
   cross = Builder.CreateInsertElement(cross, xy_yx, 2);
diff --git a/llvm/lib/Target/DirectX/DXILOpLowering.cpp b/llvm/lib/Target/DirectX/DXILOpLowering.cpp
index 63aeade9c19e4..203a24038f618 100644
--- a/llvm/lib/Target/DirectX/DXILOpLowering.cpp
+++ b/llvm/lib/Target/DirectX/DXILOpLowering.cpp
@@ -483,7 +483,7 @@ class OpLowerer {
         if (!Extracts[I])
           Extracts[I] = IRB.CreateExtractValue(Op, I);
 
-      Value *Vec = UndefValue::get(OldTy);
+      Value *Vec = PoisonValue::get(OldTy);
       for (int I = 0, E = N; I != E; ++I)
         Vec = IRB.CreateInsertElement(Vec, Extracts[I], I);
       OldResult->replaceAllUsesWith(Vec);