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

[Philip Reames via llvm-dev]

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
>         <mailto:llvm-dev at lists.llvm.org>>
>         *To: *"Renato Golin" <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
>         <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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>         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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