[llvm-dev] Existing studies on the benefits of pointer analysis

Tue Mar 22 14:41:38 PDT 2016

No pointer analysis will show any benefits until it is on by default and
tuning starts :)

or everything is tuned and then it's turned on, whichever way you want to
do it.

On Tue, Mar 22, 2016 at 2:33 PM, Jia Chen <jchen at cs.utexas.edu> wrote:

> It's something that I am certainly interested in and qualified to do.
>
> However, the way I read Daniel's reply in this thread is: "LLVM, in its
> current form, is unlikely to benefit from a more precise aa". He did
> mention that cfl-aa is "more understandable and maintainable", and is "fast
> enough", but nothing is said about the benefits. There was some discussions
> I could find back in 2014, which basically says that cfl-aa offers no
> significant improvement in performance. Things may got greatly improved
> since then, yet it is not clear to me what the current situation is.
>
> With the benefits being unclear a GSoC proposal on this topic may not look
> motivated enough.
>
>
> On 03/22/2016 01:55 PM, Philip Reames wrote:
>
> It's found more and more like "get CFL-AA turned on by default" might be a
> viable GSoC project for the right student.  It would require someone with
> existing knowledge of AA and a willingness to debug nasty problems, but it
> sounds like there's definitely interest in the community in seeing this
> happen.
>
> If the student finished early (unlikely), they could start on SCEV-AA as
> well.
>
> Philip
>
> On 03/21/2016 01:10 PM, George Burgess IV via llvm-dev wrote:
>
> As of late-August 2015, putting CFL-AA behind BasicAA caused miscompiles
> when trying to bootstrap Clang/LLVM, yeah. It didn't seem that there were
> many new errors (I think it caused ~10 tests to fail, where fail = either
> segv or produce the wrong output), but it did end up breaking things. I
> don't recall if standalone CFL-AA causes miscompiles, but I highly doubt
> the breakages I observed were BasicAA's fault.
>
> WRT speed, `time make -j14` on my box (6c/12t) didn't show a meaningful
> increase in compile time when CFL-AA gets enabled (read: it got lost in the
> noise). So, I agree that it's probably fast enough at the moment; if we
> want to enhance it, we should focus on making it bootstrap
> clang+LLVM/making it more accurate.
>
> On Mon, Mar 21, 2016 at 12:26 PM, Hal Finkel <hfinkel at anl.gov> wrote:
>
>>
>> ------------------------------
>>
>> *From: *"Daniel Berlin via llvm-dev" < <llvm-dev at lists.llvm.org>
>> llvm-dev at lists.llvm.org>
>> *To: *"Renato Golin" < <renato.golin at linaro.org>renato.golin at linaro.org>,
>> "George Burgess IV" <george.burgess.iv at gmail.com>
>> *Cc: *"llvm-dev" < <llvm-dev at lists.llvm.org>llvm-dev at lists.llvm.org>,
>> "Jia Chen" <jchen at cs.utexas.edu>
>> *Sent: *Monday, March 21, 2016 2:07:44 PM
>> *Subject: *Re: [llvm-dev] Existing studies on the benefits of pointer
>> analysis
>>
>>
>>
>> On Mon, Mar 21, 2016 at 12:05 PM, Renato Golin <renato.golin at linaro.org>
>> wrote:
>>
>>> On 21 March 2016 at 18:59, Daniel Berlin <dberlin at dberlin.org> wrote:
>>> > Which is why i've never mentioned it or used it in the community ;)
>>>
>>> Makes sense. :)
>>>
>>>
>>> > I would rather see someone spend their time getting SCEV-AA on by
>>> default or
>>> > CFL-AA on by default than doing another evaluation.
>>>
>>> But those may not be simple enough for a GSOC, that's why I mentioned it.
>>>
>>>
>> CFL-AA should just be fixing performance regressions, and maybe a little
>> bug fixing, which is hopefully easy enough.  It's already fast enough as a
>> pass.
>>
>>
>> My understanding from George is that there are self-hosting miscompiles
>> if you disable all AA except for CFL-AA. This is what is preventing us from
>> enabling it by default. George, is that right?
>>
>>  -Hal
>>
>>
>> SCEV-AA would be harder (must make SCEV-AA faster).
>>
>> The analysis could not only get us a birds view of the problem ahead,
>>> but also introduce new developers to AA, which would make their future
>>> work on SCEV-AA or CFL-AA easier. Kind of a teaching tool to get more
>>> AA-savvy people.
>>>
>>
>> Sure.
>>
>>>
>>> cheers,
>>> --renato
>>>
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>>
>>
>> --
>> Hal Finkel
>> Assistant Computational Scientist
>> Leadership Computing Facility
>> Argonne National Laboratory
>>
>
>
>
> _______________________________________________
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>
>
> --
> Best Regards,
>
> --
> Jia Chen
>
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