[clang] [Safe Buffers] Serialize unsafe_buffer_usage pragmas (PR #92031)

[Artem Dergachev via cfe-commits]

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@@ -1911,18 +1911,22 @@ SourceManager::getDecomposedIncludedLoc(FileID FID) const {
   return DecompLoc;
 }
 
-FileID SourceManager::getFirstFIDOfLoadedAST(SourceLocation Loc) const {
+unsigned SourceManager::getUniqueLoadedASTID(SourceLocation Loc) const {
   assert(isLoadedSourceLocation(Loc) &&
          "Must be a source location in a loaded PCH/Module file");
 
   auto [FID, Ignore] = getDecomposedLoc(Loc);
+  // `LoadedSLocEntryAllocBegin` stores the sorted lowest FID of each loaded
+  // allocation. Later allocations have lower FileIDs. The call below is to find
+  // the lowest FID of a loaded allocation from any FID in the same allocation.
+  // The lowest FID is used to identify a loaded allocation.
   const FileID *FirstFID =
       llvm::lower_bound(LoadedSLocEntryAllocBegin, FID, std::greater<FileID>{});
 
   assert(FirstFID &&
          "The failure to find the first FileID of a "
          "loaded AST from a loaded source location was unexpected.");
-  return *FirstFID;
+  return FirstFID->getHashValue();
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haoNoQ wrote:

Hmm can we go back to returning `FileID` here? We really shouldn't rely on the fact that the _hash_ value is equal to the  actual thing we're looking for.

https://github.com/llvm/llvm-project/pull/92031