================
@@ -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).
----------------
zhaoqi5 wrote:
Yes, `xvperm.w` is actually enough for this case.
But when legalizing `vector_shuffle`, `canonicalizeShuffleVectorByLane()` will
firstly generate `xvpermi.d` to avoid cross-lane access (similar to discussion
in https://github.com/llvm/llvm-project/pull/151633#discussion_r2247330425).
When comming to here, the masks has already changed to be `1,0,2,3,3,2,1,0`,
the already generated `xvpermi.d` is unable to be removed anyway.
I haven't come up with a good solution about this yet.
However, based solely on the masks obtained here, it is necessary to avoid
conversion here.
https://github.com/llvm/llvm-project/pull/151634
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