[X86] Add a one use check to the setcc inversion code in combineVSelectWithAllOnesOrZeros

[craig.topper]

Summary

If we're going to generate a new inverted setcc, we should make sure we will be able to remove the old setcc.

This found in a larger test case from a coworker I haven't had a chance to reduce yet.

[RKSimon]

LGTM but a test case would be useful.

lib/Target/X86/X86ISelLowering.cpp

33851

Update comment?

lib/Target/X86/X86ISelLowering.cpp

combineVSelectWithAllOnesOrZeros(SDNode *N, SelectionDAG &DAG,
   // vector floating-point selects.
   if (CondVT.getScalarSizeInBits() != VT.getScalarSizeInBits())
     return SDValue();
 
   bool TValIsAllOnes = ISD::isBuildVectorAllOnes(LHS.getNode());
   bool FValIsAllZeros = ISD::isBuildVectorAllZeros(RHS.getNode());
 
   // Try to invert the condition if true value is not all 1s and false value is
   // not all 0s.
-  if (!TValIsAllOnes && !FValIsAllZeros &&
+  if (!TValIsAllOnes && !FValIsAllZeros && Cond.hasOneUse() &&
       // Check if the selector will be produced by CMPP*/PCMP*.
       Cond.getOpcode() == ISD::SETCC &&
       // Check if SETCC has already been promoted.
       TLI.getSetCCResultType(DAG.getDataLayout(), *DAG.getContext(), VT) ==
           CondVT) {
     bool FValIsAllOnes = ISD::isBuildVectorAllOnes(RHS.getNode());
 
     if (TValIsAllZeros || FValIsAllOnes) {