[llvm] DenseMap: support enum class keys (PR #95972)

[Nikita Popov via llvm-commits]

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@@ -297,6 +297,27 @@ template <typename... Ts> struct DenseMapInfo<std::tuple<Ts...>> {
   }
 };
 
+// Provide DenseMapInfo for enum classes.
+template <typename Enum>
+struct DenseMapInfo<Enum, std::enable_if_t<std::is_enum_v<Enum>>> {
+  using UnderlyingType = std::underlying_type_t<Enum>;
+  using Info = DenseMapInfo<UnderlyingType>;
+
+  static Enum getEmptyKey() { return static_cast<Enum>(Info::getEmptyKey()); }
+
+  static Enum getTombstoneKey() {
+    return static_cast<Enum>(Info::getTombstoneKey());
+  }
+
+  static unsigned getHashValue(const Enum &Val) {
+    return Info::getHashValue(static_cast<UnderlyingType>(Val));
+  }
+
+  static bool isEqual(const Enum &LHS, const Enum &RHS) {
+    return Info::isEqual(static_cast<UnderlyingType>(LHS),
+                         static_cast<UnderlyingType>(RHS));
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nikic wrote:

Could directly compare `LHS == RHS` here?

https://github.com/llvm/llvm-project/pull/95972