[Clang[NFC] Fix bitmask for NullabilityPayload in Types.h

[xgupta]

Summary

The code is using the bit mask NullabilityKindMask which is 0x3
(00000011 in binary) to clear the bits in the NullabilityPayload variable.
Since NullabilityPayload is a 64-bit variable and NullabilityKindMask is
only a 8-bit variable(0x3), it will only affect the last 8 bits of the
variable. The higher 56 bits will remain unchanged.

Found by PVS-Studio - https://pvs-studio.com/en/blog/posts/cpp/1003/, N37.

[aaron.ballman]

clang/include/clang/APINotes/Types.h

535

I think a cleaner way to solve this is to make NullabilityKindMask be 64-bits. None of the other operations need this change, but it seems like it will be a bit more future-proof that way. WDYT?

[xgupta]

address comments

[xgupta]

clang/include/clang/APINotes/Types.h

535

Yeah, I do agree. Thanks for the suggestion.

[aaron.ballman]

LGTM!

clang/include/clang/APINotes/Types.h

 
 inline bool operator!=(const ParamInfo &LHS, const ParamInfo &RHS) {
   return !(LHS == RHS);
 }
 
 /// API notes for a function or method.
 class FunctionInfo : public CommonEntityInfo {
 private:
-  static constexpr const unsigned NullabilityKindMask = 0x3;
+  static constexpr const uint64_t NullabilityKindMask = 0x3;
   static constexpr const unsigned NullabilityKindSize = 2;
 
   static constexpr const unsigned ReturnInfoIndex = 0;
 
 public:
   // If yes, we consider all types to be non-nullable unless otherwise noted.
   // If this flag is not set, the pointer types are considered to have
   // unknown nullability.
void addTypeInfo(unsigned index, NullabilityKind kind) {
     assert(static_cast<unsigned>(kind) < NullabilityKindMask);
 
     NullabilityAudited = true;
     if (NumAdjustedNullable < index + 1)
       NumAdjustedNullable = index + 1;
 
     // Mask the bits.
     NullabilityPayload &=
         ~(NullabilityKindMask << (index * NullabilityKindSize));
 
     // Set the value.
     unsigned kindValue = (static_cast<unsigned>(kind))
                          << (index * NullabilityKindSize);
     NullabilityPayload |= kindValue;
   }
 
   /// Adds the return type info.