[clang] [clang][modules] Remove preloaded SLocEntries from PCM files (PR #66962)

[Jan Svoboda via cfe-commits]

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@@ -1986,13 +1984,15 @@ bool SourceManager::isInTheSameTranslationUnitImpl(
   if (isLoadedFileID(LOffs.first) != isLoadedFileID(ROffs.first))
     return false;
 
-  // If both are loaded from different AST files.
   if (isLoadedFileID(LOffs.first) && isLoadedFileID(ROffs.first)) {
-    auto FindTableSegment = [this](FileID FID) {
-      return llvm::upper_bound(LoadedSLocEntryTableSegments, -FID.ID - 2);
+    auto FindSLocEntryAlloc = [this](FileID FID) {
+      // FileIDs are negative, we store the beginning of each allocation (the
+      // lowest FileID), later allocations have lower FileIDs.
+      return llvm::upper_bound(LoadedSLocEntryAllocBegin, FID, std::greater{});
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jansvoboda11 wrote:

No, that's just me not being able to visualize binary search over anything else than positive increasing integers 😅

You're right, this should be `lower_bound`. `upper_bound` would report the incorrect allocation for the first `FileID`. Fixed in the latest commit and added a unit test.

https://github.com/llvm/llvm-project/pull/66962