[clang][Basic] Make SourceLocation usable as key in hash maps, NFCI

This change creates a `DenseMapInfo` trait specialization for the
SourceLocation class. The empty key, the tombstone key, and the hash
function are identical to `DenseMapInfo<unsigned>`, because we already
have hash maps that use raw the representation of `SourceLocation` as
a key.

The update of existing `DenseMap`s containing raw representation of
`SourceLocation`s will be done in a follow-up patch. As an example
the patch makes use of the new trait in one instance:
clang-tidy/google/UpgradeGoogletestCaseCheck.{h,cpp}

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D89719

1 files changed, 5 insertions, 0 deletions

diff --git a/clang/lib/Basic/SourceLocation.cpp b/clang/lib/Basic/SourceLocation.cpp
index 8cb0899..2ff1797 100644
--- a/clang/lib/Basic/SourceLocation.cpp
+++ b/clang/lib/Basic/SourceLocation.cpp
@@ -14,6 +14,7 @@
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/PrettyStackTrace.h"
 #include "clang/Basic/SourceManager.h"
+#include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/MemoryBuffer.h"
@@ -40,6 +41,10 @@ void PrettyStackTraceLoc::print(raw_ostream &OS) const {
 // SourceLocation
 //===----------------------------------------------------------------------===//
 
+unsigned SourceLocation::getHashValue() const {
+  return llvm::DenseMapInfo<unsigned>::getHashValue(ID);
+}
+
 void SourceLocation::print(raw_ostream &OS, const SourceManager &SM)const{
   if (!isValid()) {
     OS << "<invalid loc>";