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

James Molloy via llvm-dev
Thu, 12 May 2016 07:29:12 -0000

Yep, same. What's the magic rune to enable cfl-aa?

James

On Thu, 12 May 2016 at 05:58 Philip Reames via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> 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
>
> Awesome!
>
>
> 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.
>
>
> Philip
>
>
> On Wed, May 11, 2016 at 3:02 PM, Jia Chen via llvm-dev <
> 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 Austinjchen at cs.utexas.edu
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
>
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