+/// Do target-specific dag combines on floating point negations.
+static SDValue PerformFNEGCombine(SDNode *N, SelectionDAG &DAG,
+ const X86Subtarget *Subtarget) {
+ EVT VT = N->getValueType(0);
+ EVT SVT = VT.getScalarType();
+ SDValue Arg = N->getOperand(0);
+ SDLoc DL(N);
+
+ // Let legalize expand this if it isn't a legal type yet.
+ if (!DAG.getTargetLoweringInfo().isTypeLegal(VT))
+ return SDValue();
+
+ // If we're negating a FMUL node on a target with FMA, then we can avoid the
+ // use of a constant by performing (-0 - A*B) instead.
+ // FIXME: Check rounding control flags as well once it becomes available.
+ if (Arg.getOpcode() == ISD::FMUL && (SVT == MVT::f32 || SVT == MVT::f64) &&
+ Arg->getFlags()->hasNoSignedZeros() && Subtarget->hasAnyFMA()) {
+ SDValue Zero = DAG.getConstantFP(0.0, DL, VT);
+ return DAG.getNode(X86ISD::FNMSUB, DL, VT, Arg.getOperand(0),
+ Arg.getOperand(1), Zero);
+ }
+
+ // If we're negating a FMA node, then we can adjust the
+ // instruction to include the extra negation.
+ if (Arg.hasOneUse()) {
+ switch (Arg.getOpcode()) {
+ case X86ISD::FMADD:
+ return DAG.getNode(X86ISD::FNMSUB, DL, VT, Arg.getOperand(0),
+ Arg.getOperand(1), Arg.getOperand(2));
+ case X86ISD::FMSUB:
+ return DAG.getNode(X86ISD::FNMADD, DL, VT, Arg.getOperand(0),
+ Arg.getOperand(1), Arg.getOperand(2));
+ case X86ISD::FNMADD:
+ return DAG.getNode(X86ISD::FMSUB, DL, VT, Arg.getOperand(0),
+ Arg.getOperand(1), Arg.getOperand(2));
+ case X86ISD::FNMSUB:
+ return DAG.getNode(X86ISD::FMADD, DL, VT, Arg.getOperand(0),
+ Arg.getOperand(1), Arg.getOperand(2));
+ }
+ }
+ return SDValue();
+}
+