llvm dev - Mar 2016 - Existing studies on the benefits of pointer analysis

----- Original Message -----
> 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>
> Cc: "llvm-dev" <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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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>
> *To: *"Renato Golin" <renato.golin at linaro.org>,
"George Burgess IV" <
> george.burgess.iv at gmail.com>
> *Cc: *"llvm-dev" <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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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
>
>
>
>         _______________________________________________
>         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
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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