[DAGCombiner] fold sext into decrement

This is a sibling to rL357178 that I noticed we'd hit if we chose
an alternate transform in D59818.

  %z = zext i8 %x to i32
  %dec = add i32 %z, -1
  %r = sext i32 %dec to i64
  =>
  %z2 = zext i8 %x to i64
  %r = add i64 %z2, -1

https://rise4fun.com/Alive/kPP

The x86 vector diffs show a slight regression, so there's a chance
that we should limit this and the previous transform to scalars.

But given that we allowed vectors before, I'm matching that behavior
here. We should change both transforms together if that's the right
thing to do.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@357254 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index c24aafe59102a6936add60c44a0c7c007df065b2..5dccaf5f31187125e4b1855bfa997c076191fa69 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9039,6 +9039,15 @@ SDValue DAGCombiner::visitSIGN_EXTEND(SDNode *N) {
     SDValue Zext = DAG.getZExtOrTrunc(N0.getOperand(1).getOperand(0), DL, VT);
     return DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT), Zext);
   }
+  // Eliminate this sign extend by doing a decrement in the destination type:
+  // sext i32 ((zext i8 X to i32) + (-1)) to i64 --> (zext i8 X to i64) + (-1)
+  if (N0.getOpcode() == ISD::ADD && N0.hasOneUse() &&
+      isAllOnesOrAllOnesSplat(N0.getOperand(1)) &&
+      N0.getOperand(0).getOpcode() == ISD::ZERO_EXTEND &&
+      TLI.isOperationLegalOrCustom(ISD::ADD, VT)) {
+    SDValue Zext = DAG.getZExtOrTrunc(N0.getOperand(0).getOperand(0), DL, VT);
+    return DAG.getNode(ISD::ADD, DL, VT, Zext, DAG.getAllOnesConstant(DL, VT));
+  }
 
   return SDValue();
 }

diff --git a/test/CodeGen/X86/sext-i1.ll b/test/CodeGen/X86/sext-i1.ll
index d14fd755ce3dbff139bfe1868834fef462f61a61..6d548cfcdcbd30bc909a1af1140aadf629fafaa9 100644 (file)
--- a/test/CodeGen/X86/sext-i1.ll
+++ b/test/CodeGen/X86/sext-i1.ll
@@ -184,7 +184,6 @@ define i32 @zext_decrement_sext(i8 %x) {
 ; X64:       # %bb.0:
 ; X64-NEXT:    movzbl %dil, %eax
 ; X64-NEXT:    decl %eax
-; X64-NEXT:    cwtl
 ; X64-NEXT:    retq
   %z = zext i8 %x to i16
   %dec = add i16 %z, -1

diff --git a/test/CodeGen/X86/vector-sext.ll b/test/CodeGen/X86/vector-sext.ll
index 60a58cc724392abd7a2fbec548ecef7ed1af1e9c..9dae10e3f2eee172bcb119b593eee7cc11557f38 100644 (file)
--- a/test/CodeGen/X86/vector-sext.ll
+++ b/test/CodeGen/X86/vector-sext.ll
@@ -6458,28 +6458,29 @@ define <8 x i32> @zext_decremenet_sext(<8 x i8> %x) {
 ; AVX1-LABEL: zext_decremenet_sext:
 ; AVX1:       # %bb.0:
 ; AVX1-NEXT:    vpand {{.*}}(%rip), %xmm0, %xmm0
-; AVX1-NEXT:    vpcmpeqd %xmm1, %xmm1, %xmm1
-; AVX1-NEXT:    vpaddw %xmm1, %xmm0, %xmm0
-; AVX1-NEXT:    vpmovsxwd %xmm0, %xmm1
-; AVX1-NEXT:    vpshufd {{.*#+}} xmm0 = xmm0[2,3,0,1]
-; AVX1-NEXT:    vpmovsxwd %xmm0, %xmm0
-; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm1, %ymm0
+; AVX1-NEXT:    vpxor %xmm1, %xmm1, %xmm1
+; AVX1-NEXT:    vpunpckhwd {{.*#+}} xmm1 = xmm0[4],xmm1[4],xmm0[5],xmm1[5],xmm0[6],xmm1[6],xmm0[7],xmm1[7]
+; AVX1-NEXT:    vpcmpeqd %xmm2, %xmm2, %xmm2
+; AVX1-NEXT:    vpaddd %xmm2, %xmm1, %xmm1
+; AVX1-NEXT:    vpmovzxwd {{.*#+}} xmm0 = xmm0[0],zero,xmm0[1],zero,xmm0[2],zero,xmm0[3],zero
+; AVX1-NEXT:    vpaddd %xmm2, %xmm0, %xmm0
+; AVX1-NEXT:    vinsertf128 $1, %xmm1, %ymm0, %ymm0
 ; AVX1-NEXT:    retq
 ;
 ; AVX2-LABEL: zext_decremenet_sext:
 ; AVX2:       # %bb.0:
 ; AVX2-NEXT:    vpand {{.*}}(%rip), %xmm0, %xmm0
-; AVX2-NEXT:    vpcmpeqd %xmm1, %xmm1, %xmm1
-; AVX2-NEXT:    vpaddw %xmm1, %xmm0, %xmm0
-; AVX2-NEXT:    vpmovsxwd %xmm0, %ymm0
+; AVX2-NEXT:    vpmovzxwd {{.*#+}} ymm0 = xmm0[0],zero,xmm0[1],zero,xmm0[2],zero,xmm0[3],zero,xmm0[4],zero,xmm0[5],zero,xmm0[6],zero,xmm0[7],zero
+; AVX2-NEXT:    vpcmpeqd %ymm1, %ymm1, %ymm1
+; AVX2-NEXT:    vpaddd %ymm1, %ymm0, %ymm0
 ; AVX2-NEXT:    retq
 ;
 ; AVX512-LABEL: zext_decremenet_sext:
 ; AVX512:       # %bb.0:
 ; AVX512-NEXT:    vpand {{.*}}(%rip), %xmm0, %xmm0
-; AVX512-NEXT:    vpcmpeqd %xmm1, %xmm1, %xmm1
-; AVX512-NEXT:    vpaddw %xmm1, %xmm0, %xmm0
-; AVX512-NEXT:    vpmovsxwd %xmm0, %ymm0
+; AVX512-NEXT:    vpmovzxwd {{.*#+}} ymm0 = xmm0[0],zero,xmm0[1],zero,xmm0[2],zero,xmm0[3],zero,xmm0[4],zero,xmm0[5],zero,xmm0[6],zero,xmm0[7],zero
+; AVX512-NEXT:    vpcmpeqd %ymm1, %ymm1, %ymm1
+; AVX512-NEXT:    vpaddd %ymm1, %ymm0, %ymm0
 ; AVX512-NEXT:    retq
 ;
 ; X32-SSE2-LABEL: zext_decremenet_sext: