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X86: optimization for -(x != 0)

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This patch will optimize -(x != 0) on X86
FROM 
cmpl	$0x01,%edi
sbbl	%eax,%eax
notl	%eax
TO
negl %edi
sbbl %eax %eax


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155853 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Manman Ren 2012-04-30 22:51:25 +00:00
parent 7a3afa91ad
commit 16a76519a5
2 changed files with 37 additions and 0 deletions
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16
lib/Target/X86/X86ISelLowering.cpp
View File

@ -8589,6 +8589,22 @@ SDValue X86TargetLowering::LowerSELECT(SDValue Op, SelectionDAG &DAG) const {
SDValue Y = isAllOnes(Op2) ? Op1 : Op2;
SDValue CmpOp0 = Cmp.getOperand(0);
// further optimization for special cases
// (select (x != 0), -1, 0) -> neg & sbb
// (select (x == 0), 0, -1) -> neg & sbb
if (ConstantSDNode *YC = dyn_cast<ConstantSDNode>(Y))
if (YC->isNullValue() &&
(isAllOnes(Op1) == (CondCode == X86::COND_NE))) {
SDVTList VTs = DAG.getVTList(CmpOp0.getValueType(), MVT::i32);
SDValue Neg = DAG.getNode(ISD::SUB, DL, VTs,
DAG.getConstant(0, CmpOp0.getValueType()),
CmpOp0);
SDValue Res = DAG.getNode(X86ISD::SETCC_CARRY, DL, Op.getValueType(),
DAG.getConstant(X86::COND_B, MVT::i8),
SDValue(Neg.getNode(), 1));
return Res;
}
Cmp = DAG.getNode(X86ISD::CMP, DL, MVT::i32,
CmpOp0, DAG.getConstant(1, CmpOp0.getValueType()));
Cmp = ConvertCmpIfNecessary(Cmp, DAG);

21
test/CodeGen/X86/select.ll
View File

@ -218,3 +218,24 @@ define i32 @test14(i32 %a, i32 %b) nounwind {
; CHECK-NEXT: ret
}
; rdar://10961709
define i32 @test15(i32 %x) nounwind {
entry:
%cmp = icmp ne i32 %x, 0
%sub = sext i1 %cmp to i32
ret i32 %sub
; CHECK: test15:
; CHECK: negl
; CHECK: sbbl
}
define i32 @test16(i32 %x) nounwind {
entry:
%c = icmp eq i32 %x, 0
%d = select i1 %c, i32 0, i32 -1
ret i32 %d
; CHECK: test16:
; CHECK: negl
; CHECK: sbbl
}