[llvm] [LoongArch] Custom legalize vector_shuffle to `xvextrins` (PR #164375)

[via llvm-commits]

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@@ -2523,6 +2523,82 @@ static SDValue lowerVECTOR_SHUFFLE_XVPICKOD(const SDLoc &DL, ArrayRef<int> Mask,
   return DAG.getNode(LoongArchISD::VPICKOD, DL, VT, V2, V1);
 }
 
+/// Lower VECTOR_SHUFFLE into XVEXTRINS (if possible).
+static SDValue
+lowerVECTOR_SHUFFLE_XVEXTRINS(const SDLoc &DL, ArrayRef<int> Mask, MVT VT,
+                              SDValue V1, SDValue V2, SelectionDAG &DAG,
+                              const LoongArchSubtarget &Subtarget) {
+  int NumElts = VT.getVectorNumElements();
+  MVT EltVT = VT.getVectorElementType();
+  MVT GRLenVT = Subtarget.getGRLenVT();
+
+  if ((int)Mask.size() != NumElts)
+    return SDValue();
+
+  auto tryLowerToExtrAndIns = [&](int Base) -> SDValue {
+    SmallVector<int> DiffPos;
+    for (int i = 0; i < NumElts; ++i) {
+      if (Mask[i] == -1)
+        continue;
+      if (Mask[i] != Base + i) {
+        DiffPos.push_back(i);
+        if (DiffPos.size() > 2)
+          return SDValue();
+      }
+    }
+
+    // Need exactly two differing element to lower into XVEXTRINS.
+    if (DiffPos.size() != 2 || DiffPos[1] != DiffPos[0] + NumElts / 2)
+      return SDValue();
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zhaoqi5 wrote:

Great. Now support handling undef elements.

https://github.com/llvm/llvm-project/pull/164375