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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Hi Jia-<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">What apps/benchmarks do you plan to use to test the performance of cfl-aa ?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-Dibyendu<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> llvm-dev [mailto:llvm-dev-bounces@lists.llvm.org]
<b>On Behalf Of </b>George Burgess IV via llvm-dev<br>
<b>Sent:</b> Thursday, May 12, 2016 11:16 PM<br>
<b>To:</b> James Molloy <james@jamesmolloy.co.uk><br>
<b>Cc:</b> llvm-dev <llvm-dev@lists.llvm.org>; Jia Chen <jchen@cs.utexas.edu><br>
<b>Subject:</b> Re: [llvm-dev] [GSoC 2016] Introduction & Feedback - Better Alias Analysis<o:p></o:p></span></p>
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<p class="MsoNormal">> <span style="font-size:9.5pt">What's the magic rune to enable cfl-aa?</span><o:p></o:p></p>
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<p class="MsoNormal">We have two magical opt flags: -use-cfl-aa and -use-cfl-aa-in-codegen :)<o:p></o:p></p>
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<p class="MsoNormal">IIRC, both of them should cause CFLAA to be enabled as a last resort.<o:p></o:p></p>
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<p class="MsoNormal">On Thu, May 12, 2016 at 12:38 AM, Daniel Berlin <<a href="mailto:dberlin@dberlin.org" target="_blank">dberlin@dberlin.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">(Just to note: the other issue i remember with CFL-AA is that it currently causes performance loss. This is quite common when you increase precision, because things move/change things they couldn't before, and often do so without the natural
bounds imprecision provided before :P)<o:p></o:p></p>
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<p class="MsoNormal">On Thu, May 12, 2016 at 12:29 AM, James Molloy via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Yep, same. What's the magic rune to enable cfl-aa?<o:p></o:p></p>
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<p class="MsoNormal">James<o:p></o:p></p>
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<p class="MsoNormal">On Thu, 12 May 2016 at 05:58 Philip Reames via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">On 05/11/2016 05:16 PM, George Burgess IV via llvm-dev wrote:<o:p></o:p></p>
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<p class="MsoNormal">> <span style="font-size:9.5pt">After applying the patch on r267335 and bootstrap LLVM/clang with cfl-aa enabled on its own as well as behind basic-aa on an x86 machine, I ran test-suite with lit and saw no failed test cases</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">Woohoo! This is great news. :D</span><o:p></o:p></p>
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<p class="MsoNormal">Awesome!<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">I'm not sure how closely everyone is reading the intro emails, so we may get more help if we also send a slightly more targeted "Hey, CFLAA isn't obviously broken anymore. Please help us find any other problems/please
report performance numbers to us," email. Whether we do that this very second, or when GSoC actually starts, is up to you.</span><o:p></o:p></p>
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<p class="MsoNormal">Once this lands in tree, I'll do a run on our codebase to see if I see anything obvious. I suspect others can do the same.<o:p></o:p></p>
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Philip<o:p></o:p></p>
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<p class="MsoNormal">On Wed, May 11, 2016 at 3:02 PM, Jia Chen via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Dear LLVM community,<br>
<br>
I am a GSoC student this year working on the project of improving alias analysis in LLVM.<br>
<br>
The proposal initially came from a discussion I had with various devs on the mailing list some time ago [1]. The general goal of this project is to make alias analysis (in particular, cfl-aa) "better", and to be more concrete here is a list of objectives I
had in mind:<br>
<br>
- Evaluating the current state of cfl-aa, and fix all known bugs. <br>
- Improving the precision of cfl-aa. Although flow sensitivity may not be very helpful for LLVM in its current form, field sensitivity should be something important and I'll definitely try to add it to cfl-aa. Given the complexity LLVM's memory model has, my
guess is that I may need to spend most of my summer on this task.<br>
- Improving the performance of cfl-aa. (It is fairly efficient in its current form, IMO. Further performance tuning may be needed if more features such as field sensitivity were added.)<br>
- Understanding how various clients interacts with cfl-aa, and exploring various ways to minimize precision/performance losses caused by the interaction.<br>
- If time permits, maybe I can look at scev-aa and try to bring it back to the compilation pipeline.<br>
<br>
I know these objectives are not as clear cut as other GSoC projects people used to have, and it is hard to come up with a clear schedule as well as a success metric. Nevertheless even if my contributions may seem fragmented and incremental, I felt that as long
as the work is useful to the community, it is going to be the most valuable summer I've ever had as a student.<br>
<br>
** Current Status **<br>
<br>
I've submitted a simple patch last week (D19776) to fix a subtle bug in cfl-aa. After applying the patch on r267335 and bootstrap LLVM/clang with cfl-aa enabled on its own as well as behind basic-aa on an x86 machine, I ran test-suite with lit and saw no failed
test cases. I didn't time the tests in any rigorous way, but it didn't look like cfl-aa add very noticable performance overhead. It may be a good time, I think, to call for people's help to test cfl-aa on their internal codebase. If everything goes well, we
should be able to safely turn on cfl-aa by default soon.<br>
<br>
Let me conclude this introduction by saying thank you for accepting my proposal, and in particular I want to thank my mentors George and Hal for the providing me with so much support and guidance. Please let me know if you have any comments or suggestions.<br>
<br>
[1] <a href="http://lists.llvm.org/pipermail/llvm-dev/2016-March/096851.html" target="_blank">
http://lists.llvm.org/pipermail/llvm-dev/2016-March/096851.html</a><span style="color:#888888"><br>
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<o:p></o:p></span></p>
<pre><span style="color:#888888">-- <o:p></o:p></span></pre>
<pre><span style="color:#888888">Best Regards,<o:p></o:p></span></pre>
<pre><span style="color:#888888"><o:p> </o:p></span></pre>
<pre><span style="color:#888888">--<o:p></o:p></span></pre>
<pre><span style="color:#888888">Jia Chen<o:p></o:p></span></pre>
<pre><span style="color:#888888">Department of Computer Science<o:p></o:p></span></pre>
<pre><span style="color:#888888">University of Texas at Austin<o:p></o:p></span></pre>
<pre><span style="color:#888888"><a href="mailto:jchen@cs.utexas.edu" target="_blank">jchen@cs.utexas.edu</a><o:p></o:p></span></pre>
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