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Add x86-specific DAG combine to simplify:

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x == -y --> x+y == 0
 x != -y --> x+y != 0

On x86, the generated code goes from
   negl    %esi
   cmpl    %esi, %edi
   je    .LBB0_2
to
   addl    %esi, %edi
   je    .L4

This case is correctly handled for ARM with "cmn".

Patch by Manman Ren.
rdar://11245199
PR12545

llvm-svn: 155739
This commit is contained in:
Chad Rosier 2012-04-27 22:33:25 +00:00
parent ff5aec2d9d
commit d627fcbf2a
2 changed files with 50 additions and 0 deletions
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28
lib/Target/X86/X86ISelLowering.cpp
View File

@ -1223,6 +1223,7 @@ X86TargetLowering::X86TargetLowering(X86TargetMachine &TM)
setTargetDAGCombine(ISD::TRUNCATE);
setTargetDAGCombine(ISD::UINT_TO_FP);
setTargetDAGCombine(ISD::SINT_TO_FP);
setTargetDAGCombine(ISD::SETCC);
setTargetDAGCombine(ISD::FP_TO_SINT);
if (Subtarget->is64Bit())
setTargetDAGCombine(ISD::MUL);
@ -15000,6 +15001,32 @@ static SDValue PerformZExtCombine(SDNode *N, SelectionDAG &DAG,
return SDValue();
}
// Optimize x == -y --> x+y == 0
// x != -y --> x+y != 0
static SDValue PerformISDSETCCCombine(SDNode *N, SelectionDAG &DAG) {
ISD::CondCode CC = cast<CondCodeSDNode>(N->getOperand(2))->get();
SDValue LHS = N->getOperand(0);
SDValue RHS = N->getOperand(1);
if ((CC == ISD::SETNE || CC == ISD::SETEQ) && LHS.getOpcode() == ISD::SUB)
if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(LHS.getOperand(0)))
if (C->getAPIntValue() == 0 && LHS.hasOneUse()) {
SDValue addV = DAG.getNode(ISD::ADD, N->getDebugLoc(),
LHS.getValueType(), RHS, LHS.getOperand(1));
return DAG.getSetCC(N->getDebugLoc(), N->getValueType(0),
addV, DAG.getConstant(0, addV.getValueType()), CC);
}
if ((CC == ISD::SETNE || CC == ISD::SETEQ) && RHS.getOpcode() == ISD::SUB)
if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(RHS.getOperand(0)))
if (C->getAPIntValue() == 0 && RHS.hasOneUse()) {
SDValue addV = DAG.getNode(ISD::ADD, N->getDebugLoc(),
RHS.getValueType(), LHS, RHS.getOperand(1));
return DAG.getSetCC(N->getDebugLoc(), N->getValueType(0),
addV, DAG.getConstant(0, addV.getValueType()), CC);
}
return SDValue();
}
// Optimize RES = X86ISD::SETCC CONDCODE, EFLAG_INPUT
static SDValue PerformSETCCCombine(SDNode *N, SelectionDAG &DAG) {
unsigned X86CC = N->getConstantOperandVal(0);
@ -15230,6 +15257,7 @@ SDValue X86TargetLowering::PerformDAGCombine(SDNode *N,
case ISD::ZERO_EXTEND: return PerformZExtCombine(N, DAG, DCI, Subtarget);
case ISD::SIGN_EXTEND: return PerformSExtCombine(N, DAG, DCI, Subtarget);
case ISD::TRUNCATE: return PerformTruncateCombine(N, DAG, DCI);
case ISD::SETCC: return PerformISDSETCCCombine(N, DAG);
case X86ISD::SETCC: return PerformSETCCCombine(N, DAG);
case X86ISD::SHUFP: // Handle all target specific shuffles
case X86ISD::PALIGN:

22
test/CodeGen/X86/neg_cmp.ll Normal file
View File

@ -0,0 +1,22 @@
; RUN: llc < %s -march=x86-64 | FileCheck %s
; rdar://11245199
; PR12545
define void @f(i32 %x, i32 %y) nounwind uwtable ssp {
entry:
; CHECK: f:
; CHECK-NOT: neg
; CHECK: add
%sub = sub i32 0, %y
%cmp = icmp eq i32 %x, %sub
br i1 %cmp, label %if.then, label %if.end
if.then: ; preds = %entry
tail call void @g() nounwind
br label %if.end
if.end: ; preds = %if.then, %entry
ret void
}
declare void @g()