[clang] ae726fe - [SourceManager] Explicitly check for potential iterator underflow

[Jan Korous via cfe-commits]

Author: Jan Korous
Date: 2020-09-15T15:54:16-07:00
New Revision: ae726fecae9a1cc9c50de5a9f6e860056f82c556

URL: https://github.com/llvm/llvm-project/commit/ae726fecae9a1cc9c50de5a9f6e860056f82c556
DIFF: https://github.com/llvm/llvm-project/commit/ae726fecae9a1cc9c50de5a9f6e860056f82c556.diff

LOG: [SourceManager] Explicitly check for potential iterator underflow

Differential Revision: https://reviews.llvm.org/D86231

Added: 
    

Modified: 
    clang/lib/Basic/SourceManager.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
index 0a76c78cd44f..0f194403bf04 100644
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -1936,6 +1936,11 @@ SourceManager::getMacroArgExpandedLocation(SourceLocation Loc) const {
 
   assert(!MacroArgsCache->empty());
   MacroArgsMap::iterator I = MacroArgsCache->upper_bound(Offset);
+  // In case every element in MacroArgsCache is greater than Offset we can't
+  // decrement the iterator.
+  if (I == MacroArgsCache->begin())
+    return Loc;
+
   --I;
 
   unsigned MacroArgBeginOffs = I->first;