I am investigating potential code-completion speedups while using clang&#39;s code-completion mechanism. The flow described below is what I found in [rtags](https://github.com/Andersbakken/rtags), by Anders Bakken.

Translation units are parsed by a daemon monitoring files for changes. This is done by called `clang_parseTranslationUnit` and related functions(`reparse*`, `dispose*`). When the user requests a completion at a given line and column in a source file, the daemon passes the cached translation unit for the last saved version of the source file and the current source file to `clang_codeCompleteAt`. ([Clang CodeComplete docs](http://clang.llvm.org/doxygen/group__CINDEX__CODE__COMPLET.html)).

The flags passed to `clang_parseTranslationUnit`(from [CompletionThread::process, line 271](https://github.com/Andersbakken/rtags/blob/master/src/CompletionThread.cpp)) are `CXTranslationUnit_PrecompiledPreamble|CXTranslationUnit_CacheCompletionResults|CXTranslationUnit_SkipFunctionBodes`. The flags passed to `clang_codeCompleteAt`(from [CompletionThread::process, line 305](https://github.com/Andersbakken/rtags/blob/master/src/CompletionThread.cpp)) are `CXCodeComplete_IncludeMacros|CXCodeComplete_IncludeCodePatterns`.

The call to `clang_codeCompleteAt` is very slow - it takes around 3-5 seconds to obtain a completion even in the cases where the completion location is a legitimate member access code, a subset of the intended use case mentioned in the documentation of [`clang_codeCompleteAt`](http://clang.llvm.org/doxygen/group__CINDEX__CODE__COMPLET.html#ga50fedfa85d8d1517363952f2e10aa3bf). This seems way too slow by IDE code-completion standards. Is there a way of speeding this up?

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Faster code-completion with clang