From: Simon Pilgrim <llvm-dev@redking.me.uk>
Date: Thu, 12 Jul 2018 13:03:58 +0000 (+0000)
Subject: [X86][AVX] Use Zeroable mask to improve shuffle mask widening
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=2d2bdce25cef6305c8042cec41d6b78e24bc26c6;p=llvm

[X86][AVX] Use Zeroable mask to improve shuffle mask widening

Noticed while updating D42044, lowerV2X128VectorShuffle can improve the shuffle mask with the zeroable data to create a target shuffle mask to recognise more 'zero upper 128' patterns.

NOTE: lowerV4X128VectorShuffle could benefit as well but the code needs refactoring first to discriminate between SM_SentinelUndef and SM_SentinelZero for negative shuffle indices.

Differential Revision: https://reviews.llvm.org/D49092

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@336900 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index e21e2bb6894..2ffd917337c 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -4973,6 +4973,19 @@ static bool canWidenShuffleElements(ArrayRef<int> Mask,
   return true;
 }
 
+static bool canWidenShuffleElements(ArrayRef<int> Mask,
+                                    const APInt &Zeroable,
+                                    SmallVectorImpl<int> &WidenedMask) {
+  SmallVector<int, 32> TargetMask(Mask.begin(), Mask.end());
+  for (int i = 0, Size = TargetMask.size(); i < Size; ++i) {
+    if (TargetMask[i] == SM_SentinelUndef)
+      continue;
+    if (Zeroable[i])
+      TargetMask[i] = SM_SentinelZero;
+  }
+  return canWidenShuffleElements(TargetMask, WidenedMask);
+}
+
 static bool canWidenShuffleElements(ArrayRef<int> Mask) {
   SmallVector<int, 32> WidenedMask;
   return canWidenShuffleElements(Mask, WidenedMask);
@@ -13144,7 +13157,7 @@ static SDValue lowerV2X128VectorShuffle(const SDLoc &DL, MVT VT, SDValue V1,
     return SDValue();
 
   SmallVector<int, 4> WidenedMask;
-  if (!canWidenShuffleElements(Mask, WidenedMask))
+  if (!canWidenShuffleElements(Mask, Zeroable, WidenedMask))
     return SDValue();
 
   bool IsLowZero = (Zeroable & 0x3) == 0x3;
@@ -13213,7 +13226,8 @@ static SDValue lowerV2X128VectorShuffle(const SDLoc &DL, MVT VT, SDValue V1,
   //    [6]   - ignore
   //    [7]   - zero high half of destination
 
-  assert(WidenedMask[0] >= 0 && WidenedMask[1] >= 0 && "Undef half?");
+  assert((WidenedMask[0] >= 0 || IsLowZero) &&
+         (WidenedMask[1] >= 0 || IsHighZero) && "Undef half?");
 
   unsigned PermMask = 0;
   PermMask |= IsLowZero  ? 0x08 : (WidenedMask[0] << 0);
@@ -14326,6 +14340,7 @@ static SDValue lowerV4X128VectorShuffle(const SDLoc &DL, MVT VT,
   // function lowerV2X128VectorShuffle() is better solution.
   assert(VT.is512BitVector() && "Unexpected vector size for 512bit shuffle.");
 
+  // TODO - use Zeroable like we do for lowerV2X128VectorShuffle?
   SmallVector<int, 4> WidenedMask;
   if (!canWidenShuffleElements(Mask, WidenedMask))
     return SDValue();
diff --git a/test/CodeGen/X86/avx-cast.ll b/test/CodeGen/X86/avx-cast.ll
index 868e61ce5ef..4240f798bf9 100644
--- a/test/CodeGen/X86/avx-cast.ll
+++ b/test/CodeGen/X86/avx-cast.ll
@@ -20,9 +20,7 @@ define <8 x float> @castA(<4 x float> %m) nounwind uwtable readnone ssp {
 define <4 x double> @castB(<2 x double> %m) nounwind uwtable readnone ssp {
 ; AVX-LABEL: castB:
 ; AVX:       ## %bb.0:
-; AVX-NEXT:    ## kill: def $xmm0 killed $xmm0 def $ymm0
-; AVX-NEXT:    vxorps %xmm1, %xmm1, %xmm1
-; AVX-NEXT:    vblendps {{.*#+}} ymm0 = ymm0[0,1,2,3],ymm1[4,5,6,7]
+; AVX-NEXT:    vmovaps %xmm0, %xmm0
 ; AVX-NEXT:    retq
   %shuffle.i = shufflevector <2 x double> %m, <2 x double> zeroinitializer, <4 x i32> <i32 0, i32 1, i32 2, i32 2>
   ret <4 x double> %shuffle.i
@@ -33,9 +31,7 @@ define <4 x double> @castB(<2 x double> %m) nounwind uwtable readnone ssp {
 define <4 x i64> @castC(<2 x i64> %m) nounwind uwtable readnone ssp {
 ; AVX-LABEL: castC:
 ; AVX:       ## %bb.0:
-; AVX-NEXT:    ## kill: def $xmm0 killed $xmm0 def $ymm0
-; AVX-NEXT:    vxorps %xmm1, %xmm1, %xmm1
-; AVX-NEXT:    vblendps {{.*#+}} ymm0 = ymm0[0,1,2,3],ymm1[4,5,6,7]
+; AVX-NEXT:    vmovaps %xmm0, %xmm0
 ; AVX-NEXT:    retq
   %shuffle.i = shufflevector <2 x i64> %m, <2 x i64> zeroinitializer, <4 x i32> <i32 0, i32 1, i32 2, i32 2>
   ret <4 x i64> %shuffle.i