-/// performSelectCCCombine - Target-specific DAG combining for ISD::SELECT_CC
-/// to match FMIN/FMAX patterns.
-static SDValue performSelectCCCombine(SDNode *N, SelectionDAG &DAG) {
- // Try to use FMIN/FMAX instructions for FP selects like "x < y ? x : y".
- // Unless the NoNaNsFPMath option is set, be careful about NaNs:
- // vmax/vmin return NaN if either operand is a NaN;
- // only do the transformation when it matches that behavior.
-
- SDValue CondLHS = N->getOperand(0);
- SDValue CondRHS = N->getOperand(1);
- SDValue LHS = N->getOperand(2);
- SDValue RHS = N->getOperand(3);
- ISD::CondCode CC = cast<CondCodeSDNode>(N->getOperand(4))->get();
-
- unsigned Opcode;
- bool IsReversed;
- if (selectCCOpsAreFMaxCompatible(CondLHS, LHS) &&
- selectCCOpsAreFMaxCompatible(CondRHS, RHS)) {
- IsReversed = false; // x CC y ? x : y
- } else if (selectCCOpsAreFMaxCompatible(CondRHS, LHS) &&
- selectCCOpsAreFMaxCompatible(CondLHS, RHS)) {
- IsReversed = true ; // x CC y ? y : x
- } else {
- return SDValue();
- }
-
- bool IsUnordered = false, IsOrEqual;
- switch (CC) {
- default:
- return SDValue();
- case ISD::SETULT:
- case ISD::SETULE:
- IsUnordered = true;
- case ISD::SETOLT:
- case ISD::SETOLE:
- case ISD::SETLT:
- case ISD::SETLE:
- IsOrEqual = (CC == ISD::SETLE || CC == ISD::SETOLE || CC == ISD::SETULE);
- Opcode = IsReversed ? AArch64ISD::FMAX : AArch64ISD::FMIN;
- break;
-
- case ISD::SETUGT:
- case ISD::SETUGE:
- IsUnordered = true;
- case ISD::SETOGT:
- case ISD::SETOGE:
- case ISD::SETGT:
- case ISD::SETGE:
- IsOrEqual = (CC == ISD::SETGE || CC == ISD::SETOGE || CC == ISD::SETUGE);
- Opcode = IsReversed ? AArch64ISD::FMIN : AArch64ISD::FMAX;
- break;
- }
-
- // If LHS is NaN, an ordered comparison will be false and the result will be
- // the RHS, but FMIN(NaN, RHS) = FMAX(NaN, RHS) = NaN. Avoid this by checking
- // that LHS != NaN. Likewise, for unordered comparisons, check for RHS != NaN.
- if (!DAG.isKnownNeverNaN(IsUnordered ? RHS : LHS))
- return SDValue();
-
- // For xxx-or-equal comparisons, "+0 <= -0" and "-0 >= +0" will both be true,
- // but FMIN will return -0, and FMAX will return +0. So FMIN/FMAX can only be
- // used for unsafe math or if one of the operands is known to be nonzero.
- if (IsOrEqual && !DAG.getTarget().Options.UnsafeFPMath &&
- !(DAG.isKnownNeverZero(LHS) || DAG.isKnownNeverZero(RHS)))
- return SDValue();
-
- return DAG.getNode(Opcode, SDLoc(N), N->getValueType(0), LHS, RHS);
-}
-