[llvm] [DAG] canCreateUndefOrPoison - out of range vector insert/extract element indices only generate poison (PR #196720)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-selectiondag

Author: Simon Pilgrim (RKSimon)

<details>
<summary>Changes</summary>

Matches ValueTracking / GISel implementations - although testing options are limited until DAG has actual uses of UndefPoisonKind::UndefOnly

---
Full diff: https://github.com/llvm/llvm-project/pull/196720.diff


1 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (+7-4) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 0b7d8b7946f99..a221df567a10f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -5993,10 +5993,13 @@ bool SelectionDAG::canCreateUndefOrPoison(SDValue Op, const APInt &DemandedElts,
   case ISD::INSERT_VECTOR_ELT:
   case ISD::EXTRACT_VECTOR_ELT: {
     // Ensure that the element index is in bounds.
-    EVT VecVT = Op.getOperand(0).getValueType();
-    SDValue Idx = Op.getOperand(Opcode == ISD::INSERT_VECTOR_ELT ? 2 : 1);
-    KnownBits KnownIdx = computeKnownBits(Idx, Depth + 1);
-    return KnownIdx.getMaxValue().uge(VecVT.getVectorMinNumElements());
+    if (includesPoison(Kind)) {
+      EVT VecVT = Op.getOperand(0).getValueType();
+      SDValue Idx = Op.getOperand(Opcode == ISD::INSERT_VECTOR_ELT ? 2 : 1);
+      KnownBits KnownIdx = computeKnownBits(Idx, Depth + 1);
+      return KnownIdx.getMaxValue().uge(VecVT.getVectorMinNumElements());
+    }
+    return false;
   }
 
   case ISD::VECTOR_SHUFFLE: {

``````````

</details>


https://github.com/llvm/llvm-project/pull/196720