[llvm] [SelectionDAG] Fold extracts of subvector inserts (PR #201271)

[Simon Pilgrim via llvm-commits]

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@@ -27575,20 +27575,40 @@ SDValue DAGCombiner::visitEXTRACT_SUBVECTOR(SDNode *N) {
         return DAG.getSplatVector(NVT, DL, V.getOperand(0));
 
   // extract_subvector(insert_subvector(x,y,c1),c2)
+  //  --> extract_subvector(x,c2)
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RKSimon wrote:

In  t2 has multiple uses how come SimplifyMultipleUseDemandedVectorElts didn't handle the t3 case?

https://github.com/llvm/llvm-project/pull/201271