[IR] Remove ConstantFP::getZeroValueForNegation.

[craig.topper]

Summary

This was mostly used for integers which was fixed in D147492.

The only FP usage was removed in D147497.

[nikic]

LGTM

llvm/include/llvm/IR/Constants.h

class ConstantFP final : public ConstantData {
 
   ConstantFP(Type *Ty, const APFloat &V);
 
   void destroyConstantImpl();
 
 public:
   ConstantFP(const ConstantFP &) = delete;
 
-  /// Floating point negation must be implemented with f(x) = -0.0 - x. This
-  /// method returns the negative zero constant for floating point or vector
-  /// floating point types; for all other types, it returns the null value.
-  static Constant *getZeroValueForNegation(Type *Ty);
-
   /// This returns a ConstantFP, or a vector containing a splat of a ConstantFP,
   /// for the specified value in the specified type. This should only be used
   /// for simple constant values like 2.0/1.0 etc, that are known-valid both as
   /// host double and as the target format.
   static Constant *get(Type *Ty, double V);
 
   /// If Ty is a vector type, return a Constant with a splat of the given
   /// value. Otherwise return a ConstantFP for the given value.

llvm/lib/IR/Constants.cpp

Constant *ConstantFP::getZero(Type *Ty, bool Negative) {
   Constant *C = get(Ty->getContext(), NegZero);
 
   if (VectorType *VTy = dyn_cast<VectorType>(Ty))
     return ConstantVector::getSplat(VTy->getElementCount(), C);
 
   return C;
 }
 
-Constant *ConstantFP::getZeroValueForNegation(Type *Ty) {
-  if (Ty->isFPOrFPVectorTy())
-    return getNegativeZero(Ty);
-
-  return Constant::getNullValue(Ty);
-}
-
 
 // ConstantFP accessors.
 ConstantFP* ConstantFP::get(LLVMContext &Context, const APFloat& V) {
   LLVMContextImpl* pImpl = Context.pImpl;
 
   std::unique_ptr<ConstantFP> &Slot = pImpl->FPConstants[V];
 
   if (!Slot) {