[LLVMdev] [GSoC] Applying for GSoC 2015

John Criswell
Sun, 08 Mar 2015 13:34:02 -0000

On 3/8/15 8:56 AM, Mingxing Zhang wrote:
> Hello John,
>
> According to the FAQ, I can submit two proposals although at most one
> of them can be accepted.
> Thus I will prepare a proposal for each of the two projects.

Correct.  Only one proposal will be accepted.


> And, after reading the code of cfl-aa and several related papers, I've
> listed four milestones for the AA project:
>
> 1) In order to use the fast algorithm described in PLDI'13 [1], cfl-aa
> makes a simplification on the CFL defined in POPL'08 [2], which will
> lead to a reduction on precision (I've confirmed this observation with
> the author).
> Thus a quantitative measurement on how much is the reduction is needed.
>
> 2) In cfl-aa, different fields of a same struct and the whole array
> are represented by a single node.
> This is the reason of the problem 2, 4 listed in
> http://llvm.org/OpenProjects.html.
> We should split these large nodes.

I think the real question is whether the loss of precision matters, and
if so, to which uses of alias analysis.  SAFECode, for example, wants
field information to determine type safety (so that it can optimize away
type-safe loads and stores), so field sensitivity matters.  Perhaps
field sensitivity doesn't matter for other applications (e.g.,
optimization).  There's no point in improving precision if it doesn't
help the analyses that people care about most.

As part of your project, I think you should state the uses of alias
analysis/points-to analysis that you're aiming to improve and understand
whether your proposed improvements will help that use.  I would also
recommend picking a use that matters to a significant portion of the
LLVM community.

>
> 3) Handling special global variables, such as errno.
>
> 4) It seems that the current version of cfl-aa is an intraprocedural
> analysis.
> If the time is enough, I think we may extend it to an interprocedural
> analysis.
> The algorithm described in [3] can be applied to scaling it.
>
> As for the bloat-detection project, the final result should be a tool
> that is verified by known bugs and a set of newly detected bugs.

For the bloat detection tool, I would like to be convinced that dynamic
tracing will be, or can be, sufficiently efficient to be practical.  I
hate to ask, but I think you need to run an experiment with Giri to show
that dynamic slicing is going to be practical for the executions that
you expect to analyze.  Either that, or you need to explain how you can
use something more efficient than dynamic slicing (note that dynamic
slicing and dynamic tracing are not the same, so be sure you're
correctly stating which one you need).

>
> Do you have any suggestions on these objectives?

In your proposal, be sure to include a set of milestones and how long
you think you will need to achieve those milestones.  I may have said
that before, but it's worth repeating.

Regards,

John Criswell

>
> Thanks!
>
>
> [1] Fast Algorithms for Dyck-CFL-Reachability with Applications to
> Alias Analysis. PLDI'13
> [2] Demand-Driven Alias Analysis for C. POPL'08
> [3] Demand-Driven Context-Sensitive Alias Analysis for Java. ISSTA'11
>
>
> On 5 March 2015 at 09:58, Mingxing Zhang <james0zan at gmail.com
> <mailto:james0zan at gmail.com>> wrote:
>
>     Wow, that is cool!
>     I'll check about it.
>
>     Thank you!
>
>     On 4 March 2015 at 21:57, John Criswell <jtcriswel at gmail.com
>     <mailto:jtcriswel at gmail.com>> wrote:
>
>         On 3/4/15 2:18 AM, Mingxing Zhang wrote:
>>         Hello John,
>>
>>         Thank you for your advices and congratulations~
>>
>>         I'll read the code of cfl-aa and Giri first and make the
>>         decision of which project to pursue.
>>         The choice will be reported to this thread once I made the
>>         determination (hopefully within this week).
>
>         You should check for yourself, but I don't think anything
>         prevents you from submitting two proposals.  If you have time
>         to write two strong proposals, I see no problem with that.
>
>         Just make sure that any proposal you write is strong: it
>         provides a concrete explanation of what you want to do, some
>         justification for why it would benefit the community (short or
>         long term), and why you're the person qualified to do it.
>         Proposals should also include a set of milestones and expected
>         dates for completing those milestones.
>
>         Regards,
>
>         John Criswell
>
>
>>
>>         Thanks!
>>
>>
>>         On 3 March 2015 at 23:12, John Criswell <jtcriswel at
gmail.com
>>         <mailto:jtcriswel at gmail.com>> wrote:
>>
>>             Dear Mingxing,
>>
>>             I think both projects are interesting and useful.
>>
>>             Points-to analysis is something that is needed by
>>             research users of LLVM, but to the best of my knowledge,
>>             no solid implementation currently exists (although the
>>             cfl-aa work being done at Google may provide us with
>>             something; you should check into it before writing a
>>             proposal).  My interest is in a points-to analysis that
>>             is robust and is useful to both research and industry
>>             users of LLVM.  A points-to analysis proposal must
>>             indicate how it will help both of these subsets of the
>>             LLVM community, and it must argue why current efforts do
>>             not meet the requirements of both subsets of the community.
>>
>>             The runtime bloat tool also looks interesting, and your
>>             approach (at least to me) is interesting.  One question
>>             in my mind, though, is whether dynamic slicing is going
>>             to work well. Swarup Sahoo and I built a dynamic slicer
>>             for LLVM named Giri, and we found the tracing required
>>             for dynamic slicing to be slow.  For our purposes, the
>>             overhead was okay as we only needed to record execution
>>             until a crash (which happened quickly).  In your bloat
>>             tool, the program will probably run for awhile, creating
>>             a long trace record.  You should take a look at the Giri
>>             code, use it to trace some programs, and see if the
>>             overheads are going to be tolerable.  If they are not,
>>             then your first task would be to optimize Giri for your
>>             bloat tool.
>>
>>             You should also be more specific about which LLVM
>>             instructions will be traced.  For example, I wouldn't
>>             record the outputs of every LLVM instruction; I might
>>             only record the outputs of loads and stores or the end of
>>             a def-use chain.
>>
>>             I'd be interested in mentoring either project.
>>
>>             BTW, it looks like your FSE paper won an award.  Congrats.
>>
>>             Regards,
>>
>>             John Criswell
>>
>>
>>
>>
>>
>>
>>
>>             On 3/3/15 2:30 AM, Mingxing Zhang wrote:
>>>             Hi all,
>>>
>>>             As a Ph.D. student majored in Software Reliability, I
>>>             have used LLVM in many of my projects, such as the
>>>             Anticipating Invariant
>>>             (http://james0zan.github.io/AI.html) and some other
>>>             undergoing ones.
>>>             Thus, it would be a great pleasure for me if I could
>>>             take this opportunity to contribute to this awesome
project.
>>>
>>>             After reading the idea list
>>>             (http://llvm.org/OpenProjects.html), I was most
>>>             interested in the idea of improving the "Pointer
and
>>>             Alias Analysis" passes.
>>>             Could you please give me some more tips or advices on
>>>             how to get started on working on the application?
>>>
>>>             Simultaneously, I also have another idea about using
>>>             LLVM to detect runtime bloat, just like the
>>>             ThreadSanitizer tool for data races.
>>>             If there is anyone here who would like to mentor this
>>>             project, could you please find some time to review the
>>>             more detailed proposal on gist
>>>
<https://gist.github.com/james0zan/d03737c60b10d0d11d34>
>>>             and give me some feedbacks?
>>>
>>>             P.S.
>>>               I do prefer the bloat detection tool, but I'm not
sure
>>>             about whether it is suitable for GSoC.
>>>               Thus I will apply for the Alias Analysis one if it is
>>>             not suitable.
>>>
>>>             Thanks!
>>>
>>>             --
>>>             Mingxing Zhang
>>>
>>>             Tel.: +86-10-62797143 <tel:%2B86-10-62797143>
>>>             Web: http://james0zan.github.io/
>>>             Addr: Room 3-122, FIT Building, Tsinghua University,
>>>             Beijing 100084, China
>>>
>>>
>>>             _______________________________________________
>>>             LLVM Developers mailing list
>>>             LLVMdev at cs.uiuc.edu  <mailto:LLVMdev at
cs.uiuc.edu>          http://llvm.cs.uiuc.edu
>>>             http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>             /
>>
>>             --
>>             John Criswell
>>             Assistant Professor
>>             Department of Computer Science, University of Rochester
>>             http://www.cs.rochester.edu/u/criswell
>>
>>
>>
>>
>>         --
>>         Mingxing Zhang
>>
>>         Tel.: +86-10-62797143 <tel:%2B86-10-62797143>
>>         Web: http://james0zan.github.io/
>>         Addr: Room 3-122, FIT Building, Tsinghua University, Beijing
>>         100084, China
>
>
>         --
>         John Criswell
>         Assistant Professor
>         Department of Computer Science, University of Rochester
>         http://www.cs.rochester.edu/u/criswell
>
>
>
>
>     --
>     Mingxing Zhang
>
>     Tel.: +86-10-62797143 <tel:%2B86-10-62797143>
>     Web: http://james0zan.github.io/
>     Addr: Room 3-122, FIT Building, Tsinghua University, Beijing
>     100084, China
>
>
>
>
> --
> Mingxing Zhang
>
> Tel.: +86-10-62797143
> Web: http://james0zan.github.io/
> Addr: Room 3-122, FIT Building, Tsinghua University, Beijing 100084, China


--
John Criswell
Assistant Professor
Department of Computer Science, University of Rochester
http://www.cs.rochester.edu/u/criswell

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