[llvm] r314332 - [X86] Rewrite the zero vector checks in lowerV2X128VectorShuffle to use the Zeroable APInt

[Craig Topper via llvm-commits]

Author: ctopper
Date: Wed Sep 27 11:56:20 2017
New Revision: 314332

URL: http://llvm.org/viewvc/llvm-project?rev=314332&view=rev
Log:
[X86] Rewrite the zero vector checks in lowerV2X128VectorShuffle to use the Zeroable APInt

We already have zeroable bits in an APInt. We might as well use that instead of checking for an all zero BUILD_VECTOR.

Differential Revision: https://reviews.llvm.org/D37950

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=314332&r1=314331&r2=314332&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Wed Sep 27 11:56:20 2017
@@ -12085,12 +12085,12 @@ static SDValue lowerV2X128VectorShuffle(
                                                 Zeroable, Subtarget, DAG))
     return Blend;
 
-  bool IsV1Zero = ISD::isBuildVectorAllZeros(V1.getNode());
-  bool IsV2Zero = ISD::isBuildVectorAllZeros(V2.getNode());
+  bool IsLowZero = (Zeroable & 0x3) == 0x3;
+  bool IsHighZero = (Zeroable & 0xc) == 0xc;
 
   // If either input operand is a zero vector, use VPERM2X128 because its mask
   // allows us to replace the zero input with an implicit zero.
-  if (!IsV1Zero && !IsV2Zero) {
+  if (!IsLowZero && !IsHighZero) {
     // Check for patterns which can be matched with a single insert of a 128-bit
     // subvector.
     bool OnlyUsesV1 = isShuffleEquivalent(V1, V2, Mask, {0, 1, 0, 1});
@@ -12124,30 +12124,17 @@ static SDValue lowerV2X128VectorShuffle(
   //    [6]   - ignore
   //    [7]   - zero high half of destination
 
-  int MaskLO = WidenedMask[0] < 0 ? 0 : WidenedMask[0];
-  int MaskHI = WidenedMask[1] < 0 ? 0 : WidenedMask[1];
+  assert(WidenedMask[0] >= 0 && WidenedMask[1] >= 0 && "Undef half?");
 
-  unsigned PermMask = MaskLO | (MaskHI << 4);
+  unsigned PermMask = 0;
+  PermMask |= IsLowZero  ? 0x08 : (WidenedMask[0] << 0);
+  PermMask |= IsHighZero ? 0x80 : (WidenedMask[1] << 4);
 
-  // If either input is a zero vector, replace it with an undef input.
-  // Shuffle mask values <  4 are selecting elements of V1.
-  // Shuffle mask values >= 4 are selecting elements of V2.
-  // Adjust each half of the permute mask by clearing the half that was
-  // selecting the zero vector and setting the zero mask bit.
-  if (IsV1Zero) {
+  // Check the immediate mask and replace unused sources with undef.
+  if ((PermMask & 0x0a) != 0x00 && (PermMask & 0xa0) != 0x00)
     V1 = DAG.getUNDEF(VT);
-    if (MaskLO < 2)
-      PermMask = (PermMask & 0xf0) | 0x08;
-    if (MaskHI < 2)
-      PermMask = (PermMask & 0x0f) | 0x80;
-  }
-  if (IsV2Zero) {
+  if ((PermMask & 0x0a) != 0x02 && (PermMask & 0xa0) != 0x20)
     V2 = DAG.getUNDEF(VT);
-    if (MaskLO >= 2)
-      PermMask = (PermMask & 0xf0) | 0x08;
-    if (MaskHI >= 2)
-      PermMask = (PermMask & 0x0f) | 0x80;
-  }
 
   return DAG.getNode(X86ISD::VPERM2X128, DL, VT, V1, V2,
                      DAG.getConstant(PermMask, DL, MVT::i8));