[llvm-branch-commits] [llvm] DAG: Handle half spanning extract_subvector in type legalization (PR #154101)

[Matt Arsenault via llvm-branch-commits]

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@@ -3845,9 +3845,22 @@ SDValue DAGTypeLegalizer::SplitVecOp_EXTRACT_SUBVECTOR(SDNode *N) {
   unsigned NumResultElts = SubVT.getVectorMinNumElements();
 
   if (IdxVal < LoEltsMin) {
-    assert(IdxVal + NumResultElts <= LoEltsMin &&
-           "Extracted subvector crosses vector split!");
-    return DAG.getNode(ISD::EXTRACT_SUBVECTOR, dl, SubVT, Lo, Idx);
+    // If the extracted elements are all in the low half, do a simple extract.
+    if (IdxVal + NumResultElts <= LoEltsMin)
+      return DAG.getNode(ISD::EXTRACT_SUBVECTOR, dl, SubVT, Lo, Idx);
+
+    // Extracted subvector crosses vector split, so we need to blend the two
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arsenm wrote:

I wasn't sure what to do with scalable vectors. I tried to get a scalable case hit here but failed 

https://github.com/llvm/llvm-project/pull/154101