[SourceManager] Expose max usage of source location space as a Statistic

clang/include/clang/Basic/SourceManager.h

@@ -1981,6 +1981,7 @@ class SourceManager : public RefCountedBase<SourceManager> {
                                          SourceLocation SpellLoc,
                                          SourceLocation ExpansionLoc,
                                          unsigned ExpansionLength) const;
+  void updateSlocUsageStats() const;
 };
 
 /// Comparison function object.

clang/lib/Basic/SourceManager.cpp

@@ -20,6 +20,7 @@
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/Allocator.h"
@@ -46,6 +47,13 @@ using namespace clang;
 using namespace SrcMgr;
 using llvm::MemoryBuffer;
 
+#define DEBUG_TYPE "source-manager"
+
+// Reaching a limit of 2^31 results in a hard error. This metric allows to track
+// if particular invocation of the compiler is close to it.
+STATISTIC(MaxUsedSLocBytes, "Maximum number of bytes used by source locations "
+                            "(both loaded and local).");
+
 //===----------------------------------------------------------------------===//
 // SourceManager Helper Classes
 //===----------------------------------------------------------------------===//
@@ -466,6 +474,7 @@ SourceManager::AllocateLoadedSLocEntries(unsigned NumSLocEntries,
   SLocEntryLoaded.resize(LoadedSLocEntryTable.size());
   SLocEntryOffsetLoaded.resize(LoadedSLocEntryTable.size());
   CurrentLoadedOffset -= TotalSize;
+  updateSlocUsageStats();
   int BaseID = -int(LoadedSLocEntryTable.size()) - 1;
   LoadedSLocEntryAllocBegin.push_back(FileID::get(BaseID));
   return std::make_pair(BaseID, CurrentLoadedOffset);
@@ -619,6 +628,7 @@ FileID SourceManager::createFileIDImpl(ContentCache &File, StringRef Filename,
   // We do a +1 here because we want a SourceLocation that means "the end of the
   // file", e.g. for the "no newline at the end of the file" diagnostic.
   NextLocalOffset += FileSize + 1;
+  updateSlocUsageStats();
 
   // Set LastFileIDLookup to the newly created file.  The next getFileID call is
   // almost guaranteed to be from that file.
@@ -679,6 +689,7 @@ SourceManager::createExpansionLocImpl(const ExpansionInfo &Info,
   }
   // See createFileID for that +1.
   NextLocalOffset += Length + 1;
+  updateSlocUsageStats();
   return SourceLocation::getMacroLoc(NextLocalOffset - (Length + 1));
 }
 
@@ -1843,6 +1854,12 @@ void SourceManager::associateFileChunkWithMacroArgExp(
   MacroArgsCache[EndOffs] = EndOffsMappedLoc;
 }
 
+void SourceManager::updateSlocUsageStats() const {
+  SourceLocation::UIntTy UsedBytes =
+      NextLocalOffset + (MaxLoadedOffset - CurrentLoadedOffset);
+  MaxUsedSLocBytes.updateMax(UsedBytes);
+}
+
 /// If \arg Loc points inside a function macro argument, the returned
 /// location will be the macro location in which the argument was expanded.
 /// If a macro argument is used multiple times, the expanded location will