[llvm] [VectorCombine] vectorizeLoadInsert - fix shuffle when inserting into non-poison undef value (PR #119906)

[Simon Pilgrim via llvm-commits]

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@@ -179,7 +179,9 @@ bool VectorCombine::vectorizeLoadInsert(Instruction &I) {
   // Match insert into fixed vector of scalar value.
   // TODO: Handle non-zero insert index.
   Value *Scalar;
-  if (!match(&I, m_InsertElt(m_Undef(), m_Value(Scalar), m_ZeroInt())) ||
+  UndefValue *BaseVec;
+  if (!match(&I, m_InsertElt(m_UndefValue(BaseVec), m_Value(Scalar),
+                             m_ZeroInt())) ||
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RKSimon wrote:

OK - I'll simplify the fold to just handle m_Poison

https://github.com/llvm/llvm-project/pull/119906