[ADT] Allow llvm::hash_code as DenseMap key.

Summary:
This is useful when hash collisions are unlikely and acceptable, e.g. in clangd
completion ranking.

Reviewers: ioeric

Subscribers: ilya-biryukov, llvm-commits

Differential Revision: https://reviews.llvm.org/D48361

llvm-svn: 335125

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/include/llvm/ADT/DenseMapInfo.h b/llvm/include/llvm/ADT/DenseMapInfo.h
index a96904c7dbb..5d12b424fb3 100644
--- a/llvm/include/llvm/ADT/DenseMapInfo.h
+++ b/llvm/include/llvm/ADT/DenseMapInfo.h
@@ -262,6 +262,13 @@ template <typename T> struct DenseMapInfo<ArrayRef<T>> {
   }
 };
 
+template <> struct DenseMapInfo<hash_code> {
+  static inline hash_code getEmptyKey() { return hash_code(-1); }
+  static inline hash_code getTombstoneKey() { return hash_code(-2); }
+  static unsigned getHashValue(hash_code val) { return val; }
+  static bool isEqual(hash_code LHS, hash_code RHS) { return LHS == RHS; }
+};
+
 } // end namespace llvm
 
 #endif // LLVM_ADT_DENSEMAPINFO_H