[x86] Teach the decomposed shuffle/blend lowering to use an early blend

[oota-llvm.git] / lib / Target / X86 / X86ISelLowering.cpp

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 31b1ada9a855594cf2e0d1a62b1bba01f2e2b389..b63911b006fee557b8075217aa6aac7938c3f35f 100644 (file)
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -7588,12 +7588,13 @@ static SDValue lowerVectorShuffleAsBlendAndPermute(SDLoc DL, MVT VT, SDValue V1,
   return DAG.getVectorShuffle(VT, DL, V, DAG.getUNDEF(VT), PermuteMask);
 }
 
-/// \brief Generic routine to lower a shuffle and blend as a decomposed set of
-/// unblended shuffles followed by an unshuffled blend.
+/// \brief Generic routine to decompose a shuffle and blend into indepndent
+/// blends and permutes.
 ///
 /// This matches the extremely common pattern for handling combined
 /// shuffle+blend operations on newer X86 ISAs where we have very fast blend
-/// operations.
+/// operations. It will try to pick the best arrangement of shuffles and
+/// blends.
 static SDValue lowerVectorShuffleAsDecomposedShuffleBlend(SDLoc DL, MVT VT,
                                                           SDValue V1,
                                                           SDValue V2,
@@ -7613,6 +7614,16 @@ static SDValue lowerVectorShuffleAsDecomposedShuffleBlend(SDLoc DL, MVT VT,
       BlendMask[i] = i + Size;
     }
 
+  // Try to lower with the simpler initial blend strategy unless one of the
+  // input shuffles would be a no-op. We prefer to shuffle inputs as the
+  // shuffle may be able to fold with a load or other benefit. However, when
+  // we'll have to do 2x as many shuffles in order to achieve this, blending
+  // first is a better strategy.
+  if (!isNoopShuffleMask(V1Mask) && !isNoopShuffleMask(V2Mask))
+    if (SDValue BlendPerm =
+            lowerVectorShuffleAsBlendAndPermute(DL, VT, V1, V2, Mask, DAG))
+      return BlendPerm;
+
   V1 = DAG.getVectorShuffle(VT, DL, V1, DAG.getUNDEF(VT), V1Mask);
   V2 = DAG.getVectorShuffle(VT, DL, V2, DAG.getUNDEF(VT), V2Mask);
   return DAG.getVectorShuffle(VT, DL, V1, V2, BlendMask);