[NFC] Remove isConstFalseVal in favour of using isNullOrNullSplat

[david-arm]

Summary

It turns out that isConstFalseVal doesn't add any value over just
using isNullOrNullSplat, so it makes sense to remove redundant
interfaces.

[sdesmalen]

It would be nice if we could have a (scalable) vector test that uses SPLAT_VECTOR that exercises this function in some way.

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

3228–3229

It's clearly not guarded by any of the unit tests, but I think this case is now no longer supported? (i.e. if the value is 0b11111110, it should still return true if getBooleanContents returns UndefinedBooleanContent).

llvm/include/llvm/CodeGen/TargetLowering.h

public:
 
     void CommitTargetLoweringOpt(const TargetLoweringOpt &TLO);
   };
 
   /// Return if the N is a constant or constant vector equal to the true value
   /// from getBooleanContents().
   bool isConstTrueVal(const SDNode *N) const;
 
-  /// Return if the N is a constant or constant vector equal to the false value
-  /// from getBooleanContents().
-  bool isConstFalseVal(const SDNode *N) const;
-
   /// Return if \p N is a True value when extended to \p VT.
   bool isExtendedTrueVal(const ConstantSDNode *N, EVT VT, bool SExt) const;
 
   /// Try to simplify a setcc built with the specified operands and cc. If it is
   /// unable to simplify it, return a null SDValue.
   SDValue SimplifySetCC(EVT VT, SDValue N0, SDValue N1, ISD::CondCode Cond,
                         bool foldBooleans, DAGCombinerInfo &DCI,
                         const SDLoc &dl) const;

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

if (MatchStrict &&
     LHS = N.getOperand(1);
     RHS = N.getOperand(2);
     CC  = N.getOperand(3);
     return true;
   }
 
   if (N.getOpcode() != ISD::SELECT_CC ||
       !TLI.isConstTrueVal(N.getOperand(2).getNode()) ||
-      !TLI.isConstFalseVal(N.getOperand(3).getNode()))
+      !isNullOrNullSplat(N.getOperand(3)))
     return false;
 
   if (TLI.getBooleanContents(N.getValueType()) ==
       TargetLowering::UndefinedBooleanContent)
     return false;
 
   LHS = N.getOperand(0);
   RHS = N.getOperand(1);

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

case ZeroOrOneBooleanContent:
     return CVal.isOne();
   case ZeroOrNegativeOneBooleanContent:
     return CVal.isAllOnes();
   }
 
   llvm_unreachable("Invalid boolean contents");
 }
 
-bool TargetLowering::isConstFalseVal(const SDNode *N) const {
-  if (!N)
-    return false;
-
-  const ConstantSDNode *CN = dyn_cast<ConstantSDNode>(N);
-  if (!CN) {
-    const BuildVectorSDNode *BV = dyn_cast<BuildVectorSDNode>(N);
-    if (!BV)
-      return false;
-
-    // Only interested in constant splats, we don't care about undef
-    // elements in identifying boolean constants and getConstantSplatNode
-    // returns NULL if all ops are undef;
-    CN = BV->getConstantSplatNode();
-    if (!CN)
-      return false;
-  }
-
-  if (getBooleanContents(N->getValueType(0)) == UndefinedBooleanContent)
-    return !CN->getAPIntValue()[0];
-
-  return CN->isZero();
-}
-
 bool TargetLowering::isExtendedTrueVal(const ConstantSDNode *N, EVT VT,
                                        bool SExt) const {
   if (VT == MVT::i1)
     return N->isOne();
 
   TargetLowering::BooleanContent Cnt = getBooleanContents(VT);
   switch (Cnt) {
   case TargetLowering::ZeroOrOneBooleanContent:
if ((Cond == ISD::SETEQ || Cond == ISD::SETNE) &&
         // setcc (sext (setcc x, y, cc)), -1, setne) -> setcc (x, y, inv(cc))
         // setcc (sext (setcc x, y, cc)), -1, seteq) -> setcc (x, y, cc)
         SDValue TopSetCC = N0->getOperand(0);
         unsigned N0Opc = N0->getOpcode();
         bool SExt = (N0Opc == ISD::SIGN_EXTEND);
         if (TopSetCC.getValueType() == MVT::i1 && VT == MVT::i1 &&
             TopSetCC.getOpcode() == ISD::SETCC &&
             (N0Opc == ISD::ZERO_EXTEND || N0Opc == ISD::SIGN_EXTEND) &&
-            (isConstFalseVal(N1C) ||
+            (isNullOrNullSplat(N1) ||
              isExtendedTrueVal(N1C, N0->getValueType(0), SExt))) {
 
           bool Inverse = (N1C->isZero() && Cond == ISD::SETEQ) ||
                          (!N1C->isZero() && Cond == ISD::SETNE);
 
           if (!Inverse)
             return TopSetCC;