[llvm-branch-commits] [llvm] DAG: Preserve poison in more concat_vectors folds (PR #206948)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-selectiondag

Author: Matt Arsenault (arsenm)

<details>
<summary>Changes</summary>

Avoid degrading poison to undef.

---
Full diff: https://github.com/llvm/llvm-project/pull/206948.diff


1 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (+6-2) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 28160dcd8100a..34be92d3c847f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -7024,7 +7024,9 @@ static SDValue foldCONCAT_VECTORS(const SDLoc &DL, EVT VT,
   SmallVector<SDValue, 16> Elts;
   for (SDValue Op : Ops) {
     EVT OpVT = Op.getValueType();
-    if (Op.isUndef())
+    if (Op.getOpcode() == ISD::POISON)
+      Elts.append(OpVT.getVectorNumElements(), DAG.getPOISON(SVT));
+    else if (Op.getOpcode() == ISD::UNDEF)
       Elts.append(OpVT.getVectorNumElements(), DAG.getUNDEF(SVT));
     else if (Op.getOpcode() == ISD::BUILD_VECTOR)
       Elts.append(Op->op_begin(), Op->op_end());
@@ -7043,7 +7045,9 @@ static SDValue foldCONCAT_VECTORS(const SDLoc &DL, EVT VT,
 
   if (SVT.bitsGT(VT.getScalarType())) {
     for (SDValue &Op : Elts) {
-      if (Op.isUndef())
+      if (Op.getOpcode() == ISD::POISON)
+        Op = DAG.getPOISON(SVT);
+      else if (Op.getOpcode() == ISD::UNDEF)
         Op = DAG.getUNDEF(SVT);
       else
         Op = DAG.getTargetLoweringInfo().isZExtFree(Op.getValueType(), SVT)

``````````

</details>


https://github.com/llvm/llvm-project/pull/206948