[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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@@ -5062,9 +5062,27 @@ static SDValue lowerVZIP(unsigned Opc, SDValue Op0, SDValue Op1,
     Op1 = convertToScalableVector(ContainerVT, Op1, DAG, Subtarget);
   }
 
-  auto [Mask, VL] = getDefaultVLOps(IntVT, ContainerVT, DL, DAG, Subtarget);
-  SDValue Passthru = DAG.getUNDEF(ContainerVT);
-  SDValue Res = DAG.getNode(Opc, DL, ContainerVT, Op0, Op1, Passthru, Mask, VL);
+  MVT InnerVT = ContainerVT;
+  auto [Mask, VL] = getDefaultVLOps(IntVT, InnerVT, DL, DAG, Subtarget);
+  if (Op1.isUndef() && ContainerVT.bitsGT(getLMUL1VT(ContainerVT)) &&
+      (RISCVISD::RI_VUNZIP2A_VL == Opc || RISCVISD::RI_VUNZIP2B_VL == Opc)) {
+    InnerVT = ContainerVT.getHalfNumVectorElementsVT();
+    VL = DAG.getConstant(VT.getVectorNumElements() / 2, DL,
+                         Subtarget.getXLenVT());
+    Mask = getAllOnesMask(InnerVT, VL, DL, DAG);
+    unsigned HighIdx = InnerVT.getVectorElementCount().getKnownMinValue();
+    Op1 = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, InnerVT, Op0,
+                      DAG.getVectorIdxConstant(HighIdx, DL));
+    Op0 = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, InnerVT, Op0,
+                      DAG.getVectorIdxConstant(0, DL));
+  }
+
+  SDValue Passthru = DAG.getUNDEF(InnerVT);
+  SDValue Res = DAG.getNode(Opc, DL, InnerVT, Op0, Op1, Passthru, Mask, VL);
+  if (InnerVT.bitsLT(ContainerVT))
+    Res = DAG.getNode(ISD::INSERT_SUBVECTOR, DL, ContainerVT,
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topperc wrote:

getInsertSubvector?

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