[llvm] [AArch64] Use isKnownNonZero to optimize eligible compares to cmn and ccmn (PR #96349)
David Green via llvm-commits
llvm-commits at lists.llvm.org
Mon Jul 22 03:02:51 PDT 2024
================
@@ -3566,13 +3574,21 @@ static SDValue emitConditionalComparison(SDValue LHS, SDValue RHS,
Opcode = AArch64ISD::CCMN;
RHS = DAG.getConstant(Imm.abs(), DL, Const->getValueType(0));
}
- } else if (RHS.getOpcode() == ISD::SUB) {
- SDValue SubOp0 = RHS.getOperand(0);
- if (isNullConstant(SubOp0) && (CC == ISD::SETEQ || CC == ISD::SETNE)) {
- // See emitComparison() on why we can only do this for SETEQ and SETNE.
- Opcode = AArch64ISD::CCMN;
- RHS = RHS.getOperand(1);
- }
+ } else if (isCMN(RHS, CC, DAG)) {
+ Opcode = AArch64ISD::CCMN;
+ RHS = RHS.getOperand(1);
+ } else if (isCMN(LHS, CC, DAG) &&
+ (isIntEqualitySetCC(CC) ||
+ (isUnsignedIntSetCC(CC) && DAG.isKnownNeverZero(RHS)) ||
+ (isSignedIntSetCC(CC) && cannotBeIntMin(RHS, DAG)))) {
----------------
davemgreen wrote:
I think the and_ult_eq_s0s1_or case was mis-compiling because of
```
// Swap LHS and RHS if it wasn't an equality comparison
// So we don't have to worry about changing the CC
// a < b -> -b < -a
std::swap(LHS, RHS);
```
The condition needed to be updated too.
https://github.com/llvm/llvm-project/pull/96349
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