[llvm-branch-commits] [llvm] [LoongArch] Use xvperm.w for cross-lane access within a single vector (PR #151634)

[via llvm-branch-commits]

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@@ -1832,6 +1832,48 @@ static SDValue lowerVECTOR_SHUFFLE_XVSHUF4I(const SDLoc &DL, ArrayRef<int> Mask,
   return lowerVECTOR_SHUFFLE_VSHUF4I(DL, Mask, VT, V1, V2, DAG);
 }
 
+/// Lower VECTOR_SHUFFLE into XVPERM (if possible).
+static SDValue lowerVECTOR_SHUFFLE_XVPERM(const SDLoc &DL, ArrayRef<int> Mask,
+                                          MVT VT, SDValue V1, SDValue V2,
+                                          SelectionDAG &DAG) {
+  // LoongArch LASX only have XVPERM_W.
+  if (Mask.size() != 8 || (VT != MVT::v8i32 && VT != MVT::v8f32))
+    return SDValue();
+
+  unsigned NumElts = VT.getVectorNumElements();
+  unsigned HalfSize = NumElts / 2;
+  bool FrontLo = true, FrontHi = true;
+  bool BackLo = true, BackHi = true;
+
+  auto inRange = [](int val, int low, int high) {
+    return (val == -1) || (val >= low && val < high);
+  };
+
+  for (unsigned i = 0; i < HalfSize; ++i) {
+    int Fronti = Mask[i];
+    int Backi = Mask[i + HalfSize];
+
+    FrontLo &= inRange(Fronti, 0, HalfSize);
+    FrontHi &= inRange(Fronti, HalfSize, NumElts);
+    BackLo &= inRange(Backi, 0, HalfSize);
+    BackHi &= inRange(Backi, HalfSize, NumElts);
+  }
+
+  // If both the lower and upper 128-bit parts access only one half of the
+  // vector (either lower or upper), avoid using xvperm.w. The latency of
+  // xvperm.w(3) is higher than using xvshuf(1) and xvori(1).
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zhaoqi5 wrote:

OK. Thanks for your review.

https://github.com/llvm/llvm-project/pull/151634