[llvm] [InstCombine] recognize missed i128 split optimization (PR #129363)

[Simon Pilgrim via llvm-commits]

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@@ -3119,6 +3119,13 @@ static Value *matchOrConcat(Instruction &Or, InstCombiner::BuilderTy &Builder) {
       match(UpperSrc, m_BitReverse(m_Value(UpperBRev))))
     return ConcatIntrinsicCalls(Intrinsic::bitreverse, UpperBRev, LowerBRev);
 
+  Value *X;
+  if (match(LowerSrc, m_SExt(m_Value(X))) &&
+      match(UpperSrc,
+            m_SExt(m_AShr(m_Specific(X), m_SpecificInt(HalfWidth / 2 - 1))))) {
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RKSimon wrote:

This might not be HalfWidth - it will be the the scalar size of X (-1)

https://github.com/llvm/llvm-project/pull/129363