[llvm] [RISCV] Use ri.vunzip2{a,b} for e64 fixed length deinterleave(2) shuffles (PR #137217)

[Craig Topper via llvm-commits]

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@@ -5768,6 +5786,26 @@ static SDValue lowerVECTOR_SHUFFLE(SDValue Op, SelectionDAG &DAG,
     }
   }
 
+  // If this is a deinterleave(2), try using vunzip{a,b}.  This mostly catches
+  // e64 which can't match above.
+  unsigned Index = 0;
+  if (Subtarget.hasVendorXRivosVizip() &&
+      ShuffleVectorInst::isDeInterleaveMaskOfFactor(Mask, 2, Index) &&
+      1 < count_if(Mask, [](int Idx) { return Idx != -1; })) {
+    unsigned Opc =
+        Index == 0 ? RISCVISD::RI_VUNZIP2A_VL : RISCVISD::RI_VUNZIP2B_VL;
+    if (V2.isUndef())
+      return lowerVZIP(Opc, V1, V2, DL, DAG, Subtarget);
+    if (SDValue Src = foldConcatVector(V1, V2)) {
+      EVT NewVT = VT.getDoubleNumVectorElementsVT();
+      SDValue ZeroIdx = DAG.getVectorIdxConstant(0, DL);
+      Src = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, NewVT, Src, ZeroIdx);
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topperc wrote:

getExtractSubvector?

https://github.com/llvm/llvm-project/pull/137217