[llvm] [X86] combineINSERT_SUBVECTOR - fold insert_subvector(base,extract_subvector(broadcast)) -> blend shuffle(base,broadcast) (REAPPLIED) (PR #133724)

[Phoebe Wang via llvm-commits]

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@@ -58896,6 +58896,30 @@ static SDValue combineINSERT_SUBVECTOR(SDNode *N, SelectionDAG &DAG,
         Mask[i + IdxVal] = i + ExtIdxVal + VecNumElts;
       return DAG.getVectorShuffle(OpVT, dl, Vec, ExtSrc, Mask);
     }
+    // If we're broadcasting, see if we can use a blend instead of
+    // extract/insert pair. Ensure that the subvector is aligned with the
+    // insertion/extractions.
+    if ((ExtIdxVal % SubVecNumElts) == 0 && (IdxVal % SubVecNumElts) == 0 &&
+        (ExtSrc.getOpcode() == X86ISD::VBROADCAST ||
+         ExtSrc.getOpcode() == X86ISD::VBROADCAST_LOAD ||
+         (ExtSrc.getOpcode() == X86ISD::SUBV_BROADCAST_LOAD &&
+          cast<MemIntrinsicSDNode>(ExtSrc)->getMemoryVT() == SubVecVT))) {
+      if (OpVT.is256BitVector() && SubVecVT.is128BitVector()) {
+        uint64_t BlendMask = IdxVal == 0 ? 0x0F : 0xF0;
+        SDValue Blend = DAG.getNode(
+            X86ISD::BLENDI, dl, MVT::v8f32, DAG.getBitcast(MVT::v8f32, Vec),
+            DAG.getBitcast(MVT::v8f32, ExtSrc),
+            DAG.getTargetConstant(BlendMask, dl, MVT::i8));
+        return DAG.getBitcast(OpVT, Blend);
+      } else if (OpVT.is512BitVector() && SubVecVT.is256BitVector()) {
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phoebewang wrote:

Does it also work for `SubVecVT.is128BitVector()`?

https://github.com/llvm/llvm-project/pull/133724