[llvm] r351013 - [X86] More aggressive shuffle mask widening in combineExtractWithShuffle

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Sat Jan 12 08:38:56 2019
New Revision: 351013

URL: http://llvm.org/viewvc/llvm-project?rev=351013&view=rev
Log:
[X86] More aggressive shuffle mask widening in combineExtractWithShuffle

Use demanded extract index to set most of the shuffle mask to undef, making it easier to widen and peek through.

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
    llvm/trunk/test/CodeGen/X86/and-load-fold.ll

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=351013&r1=351012&r2=351013&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Sat Jan 12 08:38:56 2019
@@ -33691,6 +33691,15 @@ static SDValue combineExtractWithShuffle
       scaleShuffleMask<int>(Scale, Mask, ScaledMask);
       Mask = std::move(ScaledMask);
     } else if ((Mask.size() % NumSrcElts) == 0) {
+      // Simplify Mask based on demanded element.
+      int ExtractIdx = (int)N->getConstantOperandVal(1);
+      int Scale = Mask.size() / NumSrcElts;
+      int Lo = Scale * ExtractIdx;
+      int Hi = Scale * (ExtractIdx + 1);
+      for (int i = 0, e = (int)Mask.size(); i != e; ++i)
+        if (i < Lo || Hi <= i)
+          Mask[i] = SM_SentinelUndef;
+
       SmallVector<int, 16> WidenedMask;
       while (Mask.size() > NumSrcElts &&
              canWidenShuffleElements(Mask, WidenedMask))

Modified: llvm/trunk/test/CodeGen/X86/and-load-fold.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/and-load-fold.ll?rev=351013&r1=351012&r2=351013&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/and-load-fold.ll (original)
+++ llvm/trunk/test/CodeGen/X86/and-load-fold.ll Sat Jan 12 08:38:56 2019
@@ -7,8 +7,7 @@ define i8 @foo(<4 x i8>* %V) {
 ; CHECK-LABEL: foo:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    movd {{.*#+}} xmm0 = mem[0],zero,zero,zero
-; CHECK-NEXT:    punpcklbw {{.*#+}} xmm0 = xmm0[0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7]
-; CHECK-NEXT:    pextrw $2, %xmm0, %eax
+; CHECK-NEXT:    pextrw $1, %xmm0, %eax
 ; CHECK-NEXT:    andb $95, %al
 ; CHECK-NEXT:    # kill: def $al killed $al killed $eax
 ; CHECK-NEXT:    retq