[llvm-dev] [GSoC 2016] Introduction & Feedback - Better Alias Analysis
Jia Chen via llvm-dev
llvm-dev at lists.llvm.org
Fri May 13 07:02:56 PDT 2016
Hi Dibyendu,
All I have at this point is llvm test-suite. I also have access to
SPEC'06, which may be helpful as well. My hope is that the applications
in those benchmarks are complex enough to put enough pressure on cfl-aa.
That being said, I'm not an expert in performance testing, and I am open
to suggestions on this topic.
On 05/12/2016 11:53 PM, Das, Dibyendu wrote:
>
> Hi Jia-
>
> What apps/benchmarks do you plan to use to test the performance of
> cfl-aa ?
>
> -Dibyendu
>
> *From:*llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of
> *George Burgess IV via llvm-dev
> *Sent:* Thursday, May 12, 2016 11:16 PM
> *To:* James Molloy <james at jamesmolloy.co.uk>
> *Cc:* llvm-dev <llvm-dev at lists.llvm.org>; Jia Chen <jchen at cs.utexas.edu>
> *Subject:* Re: [llvm-dev] [GSoC 2016] Introduction & Feedback - Better
> Alias Analysis
>
> > What's the magic rune to enable cfl-aa?
>
> We have two magical opt flags: -use-cfl-aa and -use-cfl-aa-in-codegen :)
>
> IIRC, both of them should cause CFLAA to be enabled as a last resort.
>
> On Thu, May 12, 2016 at 12:38 AM, Daniel Berlin <dberlin at dberlin.org
> <mailto:dberlin at dberlin.org>> wrote:
>
> (Just to note: the other issue i remember with CFL-AA is that it
> currently causes performance loss. This is quite common when you
> increase precision, because things move/change things they
> couldn't before, and often do so without the natural bounds
> imprecision provided before :P)
>
> On Thu, May 12, 2016 at 12:29 AM, James Molloy via llvm-dev
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>
> 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 <mailto: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
> <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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--
Best Regards,
--
Jia Chen
Department of Computer Science
University of Texas at Austin
jchen at cs.utexas.edu
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