[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

clang-tools-extra/clang-tidy/google/UpgradeGoogletestCaseCheck.cpp

@@ -298,8 +298,7 @@ void UpgradeGoogletestCaseCheck::check(const MatchFinder::MatchResult &Result) {
     }
 
     if (IsInInstantiation) {
-      if (MatchedTemplateLocations.count(
-              ReplacementRange.getBegin().getRawEncoding()) == 0) {
+      if (MatchedTemplateLocations.count(ReplacementRange.getBegin()) == 0) {
         // For each location matched in a template instantiation, we check if
         // the location can also be found in `MatchedTemplateLocations`. If it
         // is not found, that means the expression did not create a match
@@ -313,8 +312,7 @@ void UpgradeGoogletestCaseCheck::check(const MatchFinder::MatchResult &Result) {
     if (IsInTemplate) {
       // We gather source locations from template matches not in template
       // instantiations for future matches.
-      MatchedTemplateLocations.insert(
-          ReplacementRange.getBegin().getRawEncoding());
+      MatchedTemplateLocations.insert(ReplacementRange.getBegin());
     }
 
     if (!AddFix) {

clang-tools-extra/clang-tidy/google/UpgradeGoogletestCaseCheck.h

@@ -33,7 +33,7 @@ public:
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
 
 private:
-  llvm::DenseSet<unsigned> MatchedTemplateLocations;
+  llvm::DenseSet<SourceLocation> MatchedTemplateLocations;
 };
 
 } // namespace google

clang/include/clang/Basic/SourceLocation.h

@@ -175,6 +175,7 @@ public:
            End.isFileID();
   }
 
+  unsigned getHashValue() const;
   void print(raw_ostream &OS, const SourceManager &SM) const;
   std::string printToString(const SourceManager &SM) const;
   void dump(const SourceManager &SM) const;
@@ -479,6 +480,27 @@ namespace llvm {
     }
   };
 
+  /// Define DenseMapInfo so that SourceLocation's can be used as keys in
+  /// DenseMap and DenseSet. This trait class is eqivalent to
+  /// DenseMapInfo<unsigned> which uses SourceLocation::ID is used as a key.
+  template <> struct DenseMapInfo<clang::SourceLocation> {
+    static clang::SourceLocation getEmptyKey() {
+      return clang::SourceLocation::getFromRawEncoding(~0U);
+    }
+
+    static clang::SourceLocation getTombstoneKey() {
+      return clang::SourceLocation::getFromRawEncoding(~0U - 1);
+    }
+
+    static unsigned getHashValue(clang::SourceLocation Loc) {
+      return Loc.getHashValue();
+    }
+
+    static bool isEqual(clang::SourceLocation LHS, clang::SourceLocation RHS) {
+      return LHS == RHS;
+    }
+  };
+
   // Teach SmallPtrSet how to handle SourceLocation.
   template<>
   struct PointerLikeTypeTraits<clang::SourceLocation> {

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>";