[llvm-dev] [GSoC 2016] Introduction & Feedback - Better Alias Analysis

Philip Reames via llvm-dev llvm-dev at lists.llvm.org
Wed May 11 21:57:41 PDT 2016

On 05/11/2016 05:16 PM, George Burgess IV via llvm-dev wrote:
> > After applying the patch on r267335 and bootstrap LLVM/clang with 
> cfl-aa enabled on its own as well as behind basic-aa on an x86 
> machine, I ran test-suite with lit and saw no failed test cases
> Woohoo! This is great news. :D
> I'm not sure how closely everyone is reading the intro emails, so we 
> may get more help if we also send a slightly more targeted "Hey, CFLAA 
> isn't obviously broken anymore. Please help us find any other 
> problems/please report performance numbers to us," email. Whether we 
> do that this very second, or when GSoC actually starts, is up to you.
Once this lands in tree, I'll do a run on our codebase to see if I see 
anything obvious.  I suspect others can do the same.

> On Wed, May 11, 2016 at 3:02 PM, Jia Chen via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>     Dear LLVM community,
>     I am a GSoC student this year working on the project of improving
>     alias analysis in LLVM.
>     The proposal initially came from a discussion I had with various
>     devs on the mailing list some time ago [1]. The general goal of
>     this project is to make alias analysis (in particular, cfl-aa)
>     "better", and to be more concrete here is a list of objectives I
>     had in mind:
>     - Evaluating the current state of cfl-aa, and fix all known bugs.
>     - Improving the precision of cfl-aa. Although flow sensitivity may
>     not be very helpful for LLVM in its current form, field
>     sensitivity should be something important and I'll definitely try
>     to add it to cfl-aa. Given the complexity LLVM's memory model has,
>     my guess is that I may need to spend most of my summer on this task.
>     - Improving the performance of cfl-aa. (It is fairly efficient in
>     its current form, IMO. Further performance tuning may be needed if
>     more features such as field sensitivity were added.)
>     - Understanding how various clients interacts with cfl-aa, and
>     exploring various ways to minimize precision/performance losses
>     caused by the interaction.
>     - If time permits, maybe I can look at scev-aa and try to bring it
>     back to the compilation pipeline.
>     I know these objectives are not as clear cut as other GSoC
>     projects people used to have, and it is hard to come up with a
>     clear schedule as well as a success metric. Nevertheless even if
>     my contributions may seem fragmented and incremental, I felt that
>     as long as the work is useful to the community, it is going to be
>     the most valuable summer I've ever had as a student.
>     ** Current Status **
>     I've submitted a simple patch last week (D19776) to fix a subtle
>     bug in cfl-aa. After applying the patch on r267335 and bootstrap
>     LLVM/clang with cfl-aa enabled on its own as well as behind
>     basic-aa on an x86 machine, I ran test-suite with lit and saw no
>     failed test cases. I didn't time the tests in any rigorous way,
>     but it didn't look like cfl-aa add very noticable performance
>     overhead. It may be a good time, I think, to call for people's
>     help to test cfl-aa on their internal codebase. If everything goes
>     well, we should be able to safely turn on cfl-aa by default soon.
>     Let me conclude this introduction by saying thank you for
>     accepting my proposal, and in particular I want to thank my
>     mentors George and Hal for the providing me with so much support
>     and guidance. Please let me know if you have any comments or
>     suggestions.
>     [1] http://lists.llvm.org/pipermail/llvm-dev/2016-March/096851.html
>     -- 
>     Best Regards,
>     --
>     Jia Chen
>     Department of Computer Science
>     University of Texas at Austin
>     jchen at cs.utexas.edu <mailto:jchen at cs.utexas.edu>
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>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
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