[cfe-dev] Cross Translational Unit Analysis in Clang Static Analyzer

Dániel Krupp via cfe-dev cfe-dev at lists.llvm.org
Fri Mar 31 08:28:49 PDT 2017

Hi All,

at the EuroLLVM'17 conference we presented our results  about a new analysis mode in clang static analyzer: Cross Translational Unit analysis.
See patch https://reviews.llvm.org/D30691
which is based on the work of A. Sidorin et al. http://lists.llvm.org/pipermail/cfe-dev/2015-October/045730.html, but without function summaries and updated to the newest Clang.

The CTU mode allows the analyzer to "inline" function calls that are defined in another TU than the one currently analyzed.
So it allows to find bugs that span multiple source files.
Without this patch the static analyzer engine, when meets an external function call,
cannot reason about the return value of a function (unknown) and the pointed values, references passed to a function as parameter are invalidated.

You can find a full patched clang 4.0 (use it with llvm commit 01609a325b5f85d88e3ab5c7d470409092436cb2 )

We have run the analysis on some reasonably-sized  (ffmpeg, curl, vim, openssl, postgresql) open source C projects and found many additional true positive reports compared to the traditional single TU mode in all projects.
This indicates that this feature would give many new results on any project.

We measured the heap usage, the analysis time and the number of new findings.
You can find the detailed comparison results here:
In summary, the number of reported bugs is ~1.5-5x times the original single TU analysis, at the cost of 1.5-5x higher analysis time, 1.5-5x max heap usage (roughly in proportion to the increase in the number of reported faults).

The design concept is described shortly in this document: http://cc.elte.hu/clang-ctu/eurollvm17/abstract.pdf

If you would like to try this analysis mode on your project please find the description of the 2 new additional analyzer scripts here:

Would be  happy to hear your opinion and experiences with this feature and would appreciate your help in reviewing the patch.

Thanks & Regards,

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