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

[Jia Chen via llvm-dev]

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 
>> <mailto:hfinkel at anl.gov>> wrote:
>>
>>
>>     ------------------------------------------------------------------------
>>
>>         *From: *"Daniel Berlin via llvm-dev" <llvm-dev at lists.llvm.org>
>>         *To: *"Renato Golin" <renato.golin at linaro.org>, "George
>>         Burgess IV" <george.burgess.iv at gmail.com
>>         <mailto:george.burgess.iv at gmail.com>>
>>         *Cc: *"llvm-dev" <llvm-dev at lists.llvm.org
>>         <mailto:llvm-dev at lists.llvm.org>>, "Jia Chen"
>>         <jchen at cs.utexas.edu <mailto: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 <mailto: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 <mailto: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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>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-- 
Best Regards,

--
Jia Chen
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