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

Tue Mar 22 12:11:11 PDT 2016

FWIW, I'd be happy to help mentoring such a project if a student is interested.

During the last LLVM Dev Meeting (the US one), I think better AA was number one in the list of requested features during the BoF on "Sophisticated Program Analysis on LLVM IR"  ( http://devmtg15.llvm.org/event/4VNY/sophisticated-program-analysis-on-llvm-ir ). 
CC John, I don't remember if there was a summary of the BoF posted online.

-- 
Mehdi

> On Mar 22, 2016, at 11:55 AM, Philip Reames via llvm-dev <llvm-dev at lists.llvm.org> 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" < <mailto:llvm-dev at lists.llvm.org>llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
>> To: "Renato Golin" < <mailto:renato.golin at linaro.org>renato.golin at linaro.org <mailto: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 < <mailto:renato.golin at linaro.org>renato.golin at linaro.org <mailto: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
>> 
>> 
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>> 
>> 
>> -- 
>> Hal Finkel
>> Assistant Computational Scientist
>> Leadership Computing Facility
>> Argonne National Laboratory
>> 
>> 
>> 
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