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[X86] combineSelect - refactor MIN/MAX detection code to make it easier to add additional select(setcc,x,y) folds. NFCI. 

I need to add some additional handling to address some of the regressions from D101074
This commit is contained in:
Simon Pilgrim 2021-06-17 13:17:51 +01:00
parent 5b3cb31edb
commit cdb4fcf9a1
1 changed files with 36 additions and 33 deletions
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69
llvm/lib/Target/X86/X86ISelLowering.cpp
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@ -41796,41 +41796,44 @@ static SDValue combineSelect(SDNode *N, SelectionDAG &DAG,
if (SDValue V = combineSelectOfTwoConstants(N, DAG))
return V;
// Canonicalize min/max:
// (x > 0) ? x : 0 -> (x >= 0) ? x : 0
// (x < -1) ? x : -1 -> (x <= -1) ? x : -1
// This allows use of COND_S / COND_NS (see TranslateX86CC) which eliminates
// the need for an extra compare against zero. e.g.
// (a - b) > 0 : (a - b) ? 0 -> (a - b) >= 0 : (a - b) ? 0
// subl %esi, %edi
// testl %edi, %edi
// movl $0, %eax
// cmovgl %edi, %eax
// =>
// xorl %eax, %eax
// subl %esi, $edi
// cmovsl %eax, %edi
//
// We can also canonicalize
// (x s> 1) ? x : 1 -> (x s>= 1) ? x : 1 -> (x s> 0) ? x : 1
// (x u> 1) ? x : 1 -> (x u>= 1) ? x : 1 -> (x != 0) ? x : 1
// This allows the use of a test instruction for the compare.
if (N->getOpcode() == ISD::SELECT && Cond.getOpcode() == ISD::SETCC &&
Cond.hasOneUse() &&
LHS == Cond.getOperand(0) && RHS == Cond.getOperand(1)) {
Cond.hasOneUse()) {
EVT CondVT = Cond.getValueType();
SDValue Cond0 = Cond.getOperand(0);
SDValue Cond1 = Cond.getOperand(1);
ISD::CondCode CC = cast<CondCodeSDNode>(Cond.getOperand(2))->get();
if ((CC == ISD::SETGT && (isNullConstant(RHS) || isOneConstant(RHS))) ||
(CC == ISD::SETLT && isAllOnesConstant(RHS))) {
ISD::CondCode NewCC = CC == ISD::SETGT ? ISD::SETGE : ISD::SETLE;
Cond = DAG.getSetCC(SDLoc(Cond), Cond.getValueType(),
Cond.getOperand(0), Cond.getOperand(1), NewCC);
return DAG.getSelect(DL, VT, Cond, LHS, RHS);
}
if (CC == ISD::SETUGT && isOneConstant(RHS)) {
ISD::CondCode NewCC = ISD::SETUGE;
Cond = DAG.getSetCC(SDLoc(Cond), Cond.getValueType(),
Cond.getOperand(0), Cond.getOperand(1), NewCC);
return DAG.getSelect(DL, VT, Cond, LHS, RHS);
// Canonicalize min/max:
// (x > 0) ? x : 0 -> (x >= 0) ? x : 0
// (x < -1) ? x : -1 -> (x <= -1) ? x : -1
// This allows use of COND_S / COND_NS (see TranslateX86CC) which eliminates
// the need for an extra compare against zero. e.g.
// (a - b) > 0 : (a - b) ? 0 -> (a - b) >= 0 : (a - b) ? 0
// subl %esi, %edi
// testl %edi, %edi
// movl $0, %eax
// cmovgl %edi, %eax
// =>
// xorl %eax, %eax
// subl %esi, $edi
// cmovsl %eax, %edi
//
// We can also canonicalize
// (x s> 1) ? x : 1 -> (x s>= 1) ? x : 1 -> (x s> 0) ? x : 1
// (x u> 1) ? x : 1 -> (x u>= 1) ? x : 1 -> (x != 0) ? x : 1
// This allows the use of a test instruction for the compare.
if (LHS == Cond0 && RHS == Cond1) {
if ((CC == ISD::SETGT && (isNullConstant(RHS) || isOneConstant(RHS))) ||
(CC == ISD::SETLT && isAllOnesConstant(RHS))) {
ISD::CondCode NewCC = CC == ISD::SETGT ? ISD::SETGE : ISD::SETLE;
Cond = DAG.getSetCC(SDLoc(Cond), CondVT, Cond0, Cond1, NewCC);
return DAG.getSelect(DL, VT, Cond, LHS, RHS);
}
if (CC == ISD::SETUGT && isOneConstant(RHS)) {
ISD::CondCode NewCC = ISD::SETUGE;
Cond = DAG.getSetCC(SDLoc(Cond), CondVT, Cond0, Cond1, NewCC);
return DAG.getSelect(DL, VT, Cond, LHS, RHS);
}
}
}