[llvm] [ADT] Refactor DenseMapInfo for integer types (NFC) (PR #155549)

[Kazu Hirata via llvm-commits]

================
@@ -101,122 +102,32 @@ template<> struct DenseMapInfo<char> {
   }
 };
 
-// Provide DenseMapInfo for unsigned chars.
-template <> struct DenseMapInfo<unsigned char> {
-  static constexpr unsigned char getEmptyKey() { return ~0; }
-  static constexpr unsigned char getTombstoneKey() { return ~0 - 1; }
-  static unsigned getHashValue(const unsigned char &Val) { return Val * 37U; }
-
-  static bool isEqual(const unsigned char &LHS, const unsigned char &RHS) {
-    return LHS == RHS;
-  }
-};
-
-// Provide DenseMapInfo for unsigned shorts.
-template <> struct DenseMapInfo<unsigned short> {
-  static constexpr unsigned short getEmptyKey() { return 0xFFFF; }
-  static constexpr unsigned short getTombstoneKey() { return 0xFFFF - 1; }
-  static unsigned getHashValue(const unsigned short &Val) { return Val * 37U; }
-
-  static bool isEqual(const unsigned short &LHS, const unsigned short &RHS) {
-    return LHS == RHS;
-  }
-};
-
-// Provide DenseMapInfo for unsigned ints.
-template<> struct DenseMapInfo<unsigned> {
-  static constexpr unsigned getEmptyKey() { return ~0U; }
-  static constexpr unsigned getTombstoneKey() { return ~0U - 1; }
-  static unsigned getHashValue(const unsigned& Val) { return Val * 37U; }
-
-  static bool isEqual(const unsigned& LHS, const unsigned& RHS) {
-    return LHS == RHS;
-  }
-};
-
-// Provide DenseMapInfo for unsigned longs.
-template<> struct DenseMapInfo<unsigned long> {
-  static constexpr unsigned long getEmptyKey() { return ~0UL; }
-  static constexpr unsigned long getTombstoneKey() { return ~0UL - 1L; }
-
-  static unsigned getHashValue(const unsigned long& Val) {
-    if constexpr (sizeof(Val) == 4)
-      return DenseMapInfo<unsigned>::getHashValue(Val);
+// Provide DenseMapInfo for all integral types except char.
+//
+// The "char" case is excluded because it uses ~0 as the empty key despite
+// "char" being a signed type.  "std::is_same_v<T, char>" is included below
----------------
kazutakahirata wrote:

@topperc Thanks!  I think it's best not to touch `char` here.

https://github.com/llvm/llvm-project/pull/155549