[X86][AVX] Add lowerVectorShuffleAsLanePermuteAndPermute for v4f64 shuffles (PR39161)

Add shuffle lowering for the case where we can shuffle the lanes into place followed by an in-lane permute.

This is mainly for cases where we can have non-repeating permutes in each lane, but for now I've just enabled it for v4f64 unary shuffles to fix PR39161 - there is no test coverage for other shuffles that might benefit yet.

We now have several cross-lane shuffle lowering methods that all do something similar - I've looked at merging some of these (notably by making the repeated mask mechanism in lowerVectorShuffleByMerging128BitLanes optional), but there is a lot of assertions/assumptions in the way that makes this tricky - I ended up going for adding yet another relatively simple method instead.

Differential Revision: https://reviews.llvm.org/D53148

llvm-svn: 344446

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -13430,6 +13430,60 @@ static SDValue lowerVectorShuffleAsSplitOrBlend(const SDLoc &DL, MVT VT,
   return lowerVectorShuffleAsDecomposedShuffleBlend(DL, VT, V1, V2, Mask, DAG);
 }
 
+/// Lower a vector shuffle crossing multiple 128-bit lanes as
+/// a lane permutation followed by a per-lane permutation.
+///
+/// This is mainly for cases where we can have non-repeating permutes
+/// in each lane.
+///
+/// TODO: This is very similar to lowerVectorShuffleByMerging128BitLanes,
+/// we should investigate merging them.
+static SDValue lowerVectorShuffleAsLanePermuteAndPermute(
+    const SDLoc &DL, MVT VT, SDValue V1, SDValue V2, ArrayRef<int> Mask,
+    SelectionDAG &DAG, const X86Subtarget &Subtarget) {
+  int NumElts = VT.getVectorNumElements();
+  int NumLanes = VT.getSizeInBits() / 128;
+  int NumEltsPerLane = NumElts / NumLanes;
+
+  SmallVector<int, 4> SrcLaneMask(NumLanes, SM_SentinelUndef);
+  SmallVector<int, 16> LaneMask(NumElts, SM_SentinelUndef);
+  SmallVector<int, 16> PermMask(NumElts, SM_SentinelUndef);
+
+  for (int i = 0; i != NumElts; ++i) {
+    int M = Mask[i];
+    if (M < 0)
+      continue;
+
+    // Ensure that each lane comes from a single source lane.
+    int SrcLane = M / NumEltsPerLane;
+    int DstLane = i / NumEltsPerLane;
+    if (!isUndefOrEqual(SrcLaneMask[DstLane], SrcLane))
+      return SDValue();
+    SrcLaneMask[DstLane] = SrcLane;
+
+    LaneMask[i] = (SrcLane * NumEltsPerLane) + (i % NumEltsPerLane);
+    PermMask[i] = (DstLane * NumEltsPerLane) + (M % NumEltsPerLane);
+  }
+
+  // If we're only shuffling a single lowest lane and the rest are identity
+  // then don't bother.
+  // TODO - isShuffleMaskInputInPlace could be extended to something like this.
+  int NumIdentityLanes = 0;
+  bool OnlyShuffleLowestLane = true;
+  for (int i = 0; i != NumLanes; ++i) {
+    if (isSequentialOrUndefInRange(PermMask, i * NumEltsPerLane, NumEltsPerLane,
+                                   i * NumEltsPerLane))
+      NumIdentityLanes++;
+    else if (SrcLaneMask[i] != 0 && SrcLaneMask[i] != NumLanes)
+      OnlyShuffleLowestLane = false;
+  }
+  if (OnlyShuffleLowestLane && NumIdentityLanes == (NumLanes - 1))
+    return SDValue();
+
+  SDValue LanePermute = DAG.getVectorShuffle(VT, DL, V1, V2, LaneMask);
+  return DAG.getVectorShuffle(VT, DL, LanePermute, DAG.getUNDEF(VT), PermMask);
+}
+
 /// Lower a vector shuffle crossing multiple 128-bit lanes as
 /// a permutation and blend of those lanes.
 ///
@@ -14166,6 +14220,11 @@ static SDValue lowerV4F64VectorShuffle(const SDLoc &DL, ArrayRef<int> Mask,
             DL, MVT::v4f64, V1, V2, Mask, Subtarget, DAG))
       return V;
 
+    // Try to permute the lanes and then use a per-lane permute.
+    if (SDValue V = lowerVectorShuffleAsLanePermuteAndPermute(
+            DL, MVT::v4f64, V1, V2, Mask, DAG, Subtarget))
+      return V;
+
     // Otherwise, fall back.
     return lowerVectorShuffleAsLanePermuteAndBlend(DL, MVT::v4f64, V1, V2, Mask,
                                                    DAG, Subtarget);
@@ -14200,6 +14259,7 @@ static SDValue lowerV4F64VectorShuffle(const SDLoc &DL, ArrayRef<int> Mask,
     if (SDValue Result = lowerVectorShuffleByMerging128BitLanes(
             DL, MVT::v4f64, V1, V2, Mask, Subtarget, DAG))
       return Result;
+
   // If we have VLX support, we can use VEXPAND.
   if (Subtarget.hasVLX())
     if (SDValue V = lowerVectorShuffleToEXPAND(DL, MVT::v4f64, Zeroable, Mask,

llvm/test/CodeGen/X86/vector-shuffle-256-v4.ll

@@ -91,9 +91,8 @@ define <4 x double> @shuffle_v4f64_0300(<4 x double> %a, <4 x double> %b) {
 define <4 x double> @shuffle_v4f64_1000(<4 x double> %a, <4 x double> %b) {
 ; AVX1-LABEL: shuffle_v4f64_1000:
 ; AVX1:       # %bb.0:
-; AVX1-NEXT:    vpermilpd {{.*#+}} xmm1 = xmm0[1,0]
-; AVX1-NEXT:    vmovddup {{.*#+}} xmm0 = xmm0[0,0]
-; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm1, %ymm0
+; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
+; AVX1-NEXT:    vpermilpd {{.*#+}} ymm0 = ymm0[1,0,2,2]
 ; AVX1-NEXT:    retq
 ;
 ; AVX2-LABEL: shuffle_v4f64_1000:
@@ -174,10 +173,8 @@ define <4 x double> @shuffle_v4f64_2222_bc(<4 x i64> %a, <4 x i64> %b) {
 define <4 x double> @shuffle_v4f64_2233(<4 x double> %a, <4 x double> %b) {
 ; AVX1-LABEL: shuffle_v4f64_2233:
 ; AVX1:       # %bb.0:
-; AVX1-NEXT:    vextractf128 $1, %ymm0, %xmm0
-; AVX1-NEXT:    vmovddup {{.*#+}} xmm1 = xmm0[0,0]
-; AVX1-NEXT:    vpermilpd {{.*#+}} xmm0 = xmm0[1,1]
-; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm1, %ymm0
+; AVX1-NEXT:    vperm2f128 {{.*#+}} ymm0 = ymm0[2,3,2,3]
+; AVX1-NEXT:    vpermilpd {{.*#+}} ymm0 = ymm0[0,0,3,3]
 ; AVX1-NEXT:    retq
 ;
 ; AVX2-LABEL: shuffle_v4f64_2233:
@@ -766,9 +763,8 @@ define <4 x i64> @shuffle_v4i64_0300(<4 x i64> %a, <4 x i64> %b) {
 define <4 x i64> @shuffle_v4i64_1000(<4 x i64> %a, <4 x i64> %b) {
 ; AVX1-LABEL: shuffle_v4i64_1000:
 ; AVX1:       # %bb.0:
-; AVX1-NEXT:    vpermilps {{.*#+}} xmm1 = xmm0[2,3,0,1]
-; AVX1-NEXT:    vpermilps {{.*#+}} xmm0 = xmm0[0,1,0,1]
-; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm1, %ymm0
+; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
+; AVX1-NEXT:    vpermilpd {{.*#+}} ymm0 = ymm0[1,0,2,2]
 ; AVX1-NEXT:    retq
 ;
 ; AVX2-LABEL: shuffle_v4i64_1000: