<rdar://problem/13479539> Only rebuild the global module cache when we're allowed to.

This eliminates excessive rebuilds of the global module cache.

llvm-svn: 177766

clang/lib/Frontend/CompilerInstance.cpp

@@ -62,7 +62,8 @@ void CompilerInstance::setInvocation(CompilerInvocation *Value) {
 
 bool CompilerInstance::shouldBuildGlobalModuleIndex() const {
   return (BuildGlobalModuleIndex ||
-          (ModuleManager && ModuleManager->isGlobalIndexUnavailable())) &&
+          (ModuleManager && ModuleManager->isGlobalIndexUnavailable() &&
+           getFrontendOpts().GenerateGlobalModuleIndex)) &&
          !ModuleBuildFailed;
 }