Is libclang slower than using clang driver based tool?

I am writing an autocompletion and syntax tool using libclang. I am pretty much using the same code as in c-index-test.c file. But the speed of results is very slow. There are few non libclang clang tools which works faster than my libclang tool.

Is there any optimization I can do to get 开发者_如何学Goresults faster? My code is pretty much as follows:

CXIndex cidx = CreateIndex(0,0);
TU = clang_parseTranslationUnit(Cidx, 0, argv, argc,0,0...); 

and so on.

Even the very first time I run clang tool, they seem to be faster.

Codebase I am working is huge.