Index: clang/tools/libclang/Indexing.cpp
===================================================================
--- clang/tools/libclang/Indexing.cpp
+++ clang/tools/libclang/Indexing.cpp
@@ -132,7 +132,7 @@
     Set = ParsedRegions;
   }
 
-  void update(ArrayRef<PPRegion> Regions) {
+  void update(const PPRegionSetTy& Regions) {
     std::lock_guard<std::mutex> MG(Mux);
     ParsedRegions.insert(Regions.begin(), Regions.end());
   }
@@ -144,7 +144,8 @@
   Preprocessor &PP;
 
   PPRegionSetTy ParsedRegions;
-  SmallVector<PPRegion, 32> NewParsedRegions;
+  PPRegionSetTy NewParsedRegions;
+
   PPRegion LastRegion;
   bool LastIsParsed;
 
@@ -166,9 +167,9 @@
       return LastIsParsed;
 
     LastRegion = region;
-    LastIsParsed = ParsedRegions.count(region);
+    LastIsParsed = NewParsedRegions.count(region) || ParsedRegions.count(region);
     if (!LastIsParsed)
-      NewParsedRegions.push_back(region);
+      NewParsedRegions.insert(std::move(region));
     return LastIsParsed;
   }