[llvm-dev] Patches for enabling clang's noundef analysis by default (original) (raw)
Juneyoung Lee via llvm-dev llvm-dev at lists.llvm.org
Mon Aug 23 00:41:18 PDT 2021
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Hello all,
I would like to get feedback for two patches that enable clang's noundef analysis flag by default. The two patches are: https://reviews.llvm.org/D105169 , https://reviews.llvm.org/D108453 . They are splitted for readability, but they will be merged into one commit and pushed if accepted.
The noundef analysis flag was added by D81678 <
https://reviews.llvm.org/D81678> in the past.
Its goal is to mark arguments and return values in C/C++ as noundef if
legal.
Besides its performance benefit to sanitizers, which was the main
motivation, attaching noundef is beneficial because it allows quite a few
optimizations that are unsound w.r.t. undef or poison (they are usually
guarded with isGuaranteedNotToBeUndefOrPoison check).
Since the fact that arg/ret values are noundef is derived from the source
language (C/C++)'s specification, the information is permanently lost
unless explicitly attached by clang (as other dereferenceable/align/...
attributes from C/C++ do).
Previously, the flag was not activated by default because it required a lot of tests to be updated. This can raise conflicts with downstream patches (discussed in this thread: D82317 <https://reviews.llvm.org/D82317>)
To avoid conflicts, I'd like to update requested tests by simply adding
-disable-noundef-analysis at // RUN: %clang_cc1 ... rather than
updating their texts (which is what D108453 is already doing).
For the requested directories or tests, I'll simply add the flag to the
RUN: command.
This will reduce the opportunity of raising conflicts with downstreams.
Any questions or concerns about enabling the flag are appreciated. The two patches are written by Hyeongyu Kim, and I'm a messenger for the patches. :)
Sincerely, Juneyoung -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20210823/0a7e8531/attachment.html>
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