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It's something that I am certainly interested in and qualified to
do.<br>
<br>
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.<br>
<br>
With the benefits being unclear a GSoC proposal on this topic may
not look motivated enough.<br>
<br>
<div class="moz-cite-prefix">On 03/22/2016 01:55 PM, Philip Reames
wrote:<br>
</div>
<blockquote cite="mid:56F19533.4030702@philipreames.com" type="cite">
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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.<br>
<br>
If the student finished early (unlikely), they could start on
SCEV-AA as well. <br>
<br>
Philip<br>
<br>
<div class="moz-cite-prefix">On 03/21/2016 01:10 PM, George
Burgess IV via llvm-dev wrote:<br>
</div>
<blockquote
cite="mid:CAKh6zBE6m31RNz1DXNU56j9asZpZAAHnbLUB0qigpduJGXaPVw@mail.gmail.com"
type="cite">
<div dir="ltr">
<div><span
style="color:rgb(0,0,0);font-family:arial,helvetica,sans-serif;font-size:13.3333px">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.</span></div>
<div><span
style="color:rgb(0,0,0);font-family:arial,helvetica,sans-serif;font-size:13.3333px"><br>
</span></div>
<div><font color="#000000" face="arial, helvetica, sans-serif"><span
style="font-size:13.3333px">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.</span></font></div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Mar 21, 2016 at 12:26 PM,
Hal Finkel <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:hfinkel@anl.gov" target="_blank">hfinkel@anl.gov</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div
style="font-family:arial,helvetica,sans-serif;font-size:10pt;color:#000000"><br>
<hr>
<blockquote style="border-left:2px solid
rgb(16,16,255);margin-left:5px;padding-left:5px;color:rgb(0,0,0);font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt"><b>From:
</b>"Daniel Berlin via llvm-dev" <<a
moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:llvm-dev@lists.llvm.org"><a class="moz-txt-link-abbreviated" href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a></a>><br>
<b>To: </b>"Renato Golin" <<a
moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:renato.golin@linaro.org"><a class="moz-txt-link-abbreviated" href="mailto:renato.golin@linaro.org">renato.golin@linaro.org</a></a>>,
"George Burgess IV" <<a moz-do-not-send="true"
href="mailto:george.burgess.iv@gmail.com"
target="_blank">george.burgess.iv@gmail.com</a>><br>
<b>Cc: </b>"llvm-dev" <<a
moz-do-not-send="true"
href="mailto:llvm-dev@lists.llvm.org"
target="_blank"><a class="moz-txt-link-abbreviated" href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a></a>>,
"Jia Chen" <<a moz-do-not-send="true"
href="mailto:jchen@cs.utexas.edu"
target="_blank">jchen@cs.utexas.edu</a>><br>
<b>Sent: </b>Monday, March 21, 2016 2:07:44 PM<br>
<b>Subject: </b>Re: [llvm-dev] Existing studies
on the benefits of pointer analysis<span><br>
<br>
<div dir="ltr"><br>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Mar 21,
2016 at 12:05 PM, Renato Golin <span
dir="ltr"><<a moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:renato.golin@linaro.org">renato.golin@linaro.org</a>></span>
wrote:<br>
<blockquote class="gmail_quote"
style="margin:0pt 0pt 0pt
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex"><span>On
21 March 2016 at 18:59, Daniel Berlin
<<a moz-do-not-send="true"
href="mailto:dberlin@dberlin.org"
target="_blank">dberlin@dberlin.org</a>>
wrote:<br>
> Which is why i've never mentioned
it or used it in the community ;)<br>
<br>
</span>Makes sense. :)<br>
<span><br>
<br>
> I would rather see someone spend
their time getting SCEV-AA on by
default or<br>
> CFL-AA on by default than doing
another evaluation.<br>
<br>
</span>But those may not be simple
enough for a GSOC, that's why I
mentioned it.<br>
<br>
</blockquote>
<div><br>
</div>
<div>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.</div>
</div>
</div>
</div>
</span></blockquote>
<br>
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?<br>
<br>
-Hal<br>
<blockquote style="border-left:2px solid
rgb(16,16,255);margin-left:5px;padding-left:5px;color:rgb(0,0,0);font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt"><span>
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">
<div><br>
</div>
<div>SCEV-AA would be harder (must make
SCEV-AA faster).</div>
<div><br>
</div>
<blockquote class="gmail_quote"
style="margin:0pt 0pt 0pt
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex"> The
analysis could not only get us a birds
view of the problem ahead,<br>
but also introduce new developers to AA,
which would make their future<br>
work on SCEV-AA or CFL-AA easier. Kind
of a teaching tool to get more<br>
AA-savvy people.<br>
</blockquote>
<div><br>
</div>
<div>Sure. </div>
<blockquote class="gmail_quote"
style="margin:0pt 0pt 0pt
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex"> <br>
cheers,<br>
--renato<br>
</blockquote>
</div>
<br>
</div>
</div>
<br>
</span><span>_______________________________________________<br>
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target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><br>
</span></blockquote>
<span><font color="#888888"><br>
<br>
<br>
-- <br>
<div><span name="x"></span>Hal Finkel<br>
Assistant Computational Scientist<br>
Leadership Computing Facility<br>
Argonne National Laboratory<span name="x"></span><br>
</div>
</font></span></div>
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</div>
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<br>
</blockquote>
-- <br>
Best Regards,<br>
<br>
--<br>
Jia Chen<br>
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