Fix a longstanding (but previously unknown) bug in the lazy

deserialization of precompiled headers, where the deserialization of
the source location entry for a buffer (e.g., macro instantiation
scratch space) would overwrite a one-element FileID cache in the
source manager. When tickled at the wrong time, we would return the
wrong decomposed source location and eventually cause c-index-test to
crash.

Found by dumb luck. It's amazing this hasn't shown up before.

llvm-svn: 98940

clang/lib/Basic/SourceManager.cpp

@@ -411,7 +411,7 @@ FileID SourceManager::createFileID(const ContentCache *File,
       = SLocEntry::get(Offset, FileInfo::get(IncludePos, File, FileCharacter));
     SLocEntryLoaded[PreallocatedID] = true;
     FileID FID = FileID::get(PreallocatedID);
-    return LastFileIDLookup = FID;
+    return FID;
   }
 
   SLocEntryTable.push_back(SLocEntry::get(NextOffset,

clang/test/Index/c-index-getCursor-test.m

@@ -52,6 +52,12 @@ int main (int argc, const char * argv[]) {
   main(someEnum, (const char **)bee);
 }
 
+#define CONCAT(X, Y) X##Y
+
+void f() {
+   int CONCAT(my,_var);
+}
+
 // CHECK: [1:1 - 3:1] Invalid Cursor => NoDeclFound
 // CHECK: [3:1 - 7:1] ObjCInterfaceDecl=Foo:3:12
 // CHECK: [7:1 - 7:7] ObjCInstanceMethodDecl=foo:7:1