<div dir="ltr">Victor, please file a bug tracking the issue. We can put relevant information there including test cases used in the experiment etc.<div><br></div><div>thanks,</div><div><br></div><div>David</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Feb 7, 2018 at 2:15 PM, Victor Leschuk <span dir="ltr"><<a href="mailto:vleschuk@accesssoftek.com" target="_blank">vleschuk@accesssoftek.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>David, could you please clarify on which code did you gain 10%
improvement? I have run numerous tests with and w/o this option
and it looks like it has no effect on performance (I am talking of
the old 2016 sample to be concrete). Maybe we could investigate it
together? Just tell me where to start?<br>
</p><div><div class="h5">
<br>
<div class="m_-7612381275907462952moz-cite-prefix">On 02/07/2018 02:11 AM, Xinliang David
Li wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Victor, thanks for the experiment.
<div><br>
</div>
<div>My suspicion is it is due to the remaining issues with
block layout -- especially with loop rotation (with PGO).
Another problem is that tail dup is not happening after loop
rotation which can limit the effectiveness of loop rotation.</div>
<div><br>
</div>
<div>I tried the internal option -mllvm
-force-precise-rotation-cost and there is about 10% speedup
with -fprofile-use. This option turns on more precise cost
model when computing rotation strategy but it is not turned on
by default.</div>
<div><br>
</div>
<div>+carrot who is working on this area.</div>
<div><br>
</div>
<div>thanks,</div>
<div><br>
</div>
<div>David</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Tue, Feb 6, 2018 at 1:37 PM, Victor
Leschuk <span dir="ltr"><<a href="mailto:vleschuk@accesssoftek.com" target="_blank">vleschuk@accesssoftek.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>Hello David, thanks for detailed response!</p>
<p>Do you have any tests that you use to measure the PGO
effectiveness? I have tested clang version 6.0 with the
same sample that Jie Chen used in 2016 and actually both
frontend-based PGO and IR-based make code run slower,
see the average time:</p>
<p>clang++ -O3: 3.15 sec </p>
<p>clang++ -O3 and -fprofile-instr-use: 3.160 sec<br>
</p>
<p>clang++ -O3 and -fprofile-use: 3.180 sec<br>
</p>
<p>g++ (7.3.0) -O3: 3.640 sec<br>
</p>
<p>g++ (7.3.0) -O3 and -fprofile-use: 2.92 sec</p>
<p>Do you have any idea what can be wrong? Maybe there are
some recommendations in which cases one should use PGO
with clang and when it is better not to do it?</p>
<p>Thanks!<br>
</p>
<div>
<div class="m_-7612381275907462952h5"> <br>
<div class="m_-7612381275907462952m_-5231669173907304757moz-cite-prefix">On
02/05/2018 09:38 AM, Xinliang David Li wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr"><br>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Sun, Feb 4, 2018 at
9:59 PM, Victor Leschuk <span dir="ltr"><<a href="mailto:vleschuk@accesssoftek.com" target="_blank">vleschuk@accesssoftek.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello David!<br>
<br>
I have recently started acquaintance with
PGO in LLVM/clang and found<br>
your e-mail thread:<br>
<a href="http://lists.llvm.org/pipermail/llvm-dev/2016-May/099395.html" rel="noreferrer" target="_blank">http://lists.llvm.org/pipermai<wbr>l/llvm-dev/2016-May/099395.htm<wbr>l</a>
. Here you<br>
posted a nice list of optimizations that use
profiling and of those<br>
which could be using but don't. However that
thread is about 2 years<br>
old. Could you please kindly let me know if
there were any significant<br>
changes in this area since that time?<br>
</blockquote>
<div><br>
</div>
<div><br>
</div>
<div>Yes, there were quite some changes since
then. Here are some of the new features:</div>
<div><br>
</div>
<div>* LLVM IR based PGO -- this is designed
to maximize program performance. The option
to turn it on is
-fprofile-generate/-fprofile-u<wbr>se</div>
<div>* value profiling support in PGO --
currently support indirect call target
profiling and memcpy/memset size profiling
and optimizations</div>
<div>* Profile data is made available for
inliner to use (enabled only for the new
pass manager: -fexperimental-new-pass-manage<wbr>r)</div>
<div>* Profile aware LICM is available --
implemented via a profile driven code
sinking pass </div>
<div>* Partial inlining is made profile
aware; Graham Yu also added support for
multiple region function outlining (with
PGO)</div>
<div>* BB layout heuristics are tuned with PGO</div>
<div>* hotness driven function layout
optimization </div>
<div><br>
</div>
<div>There are pending work in the following
area:</div>
<div>* profile aware loop vectorization, etc</div>
<div>* control heigh reduction optimization
(Hiroshi is working on this)</div>
<div><br>
</div>
<div>ThinLTO also works well with PGO.</div>
<div><br>
</div>
<div>Hope this helps.</div>
<div><br>
</div>
<div>David</div>
<div><br>
</div>
<div>
<pre style="white-space:pre-wrap;color:rgb(0,0,0);font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial">><i> What I can tell you is that there are many missing ones (that can benefit
</i>from profile): such as profile aware LICM (patch pending), speculative PRE,
loop unrolling, loop peeling, auto vectorization, inlining, function
splitting, function layout, function outlinling, profile driven size
optimization, induction variable optimization/strength reduction, stringOp
specialization/optimization/in<wbr>lining, switch peeling/lowering etc. The
biggest profile user today include ralloc, BB layout, ifcvt, shrinkwrapping
etc, but there should be rooms to be improvement there too.</pre>
<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> <br>
Thanks in advance!<br>
<span class="m_-7612381275907462952m_-5231669173907304757HOEnZb"><font color="#888888"><br>
--<br>
Best Regards,<br>
<br>
Victor Leschuk | Software Engineer |
Access Softek<br>
<br>
</font></span></blockquote>
</div>
<br>
</div>
</div>
</blockquote>
<br>
<pre class="m_-7612381275907462952m_-5231669173907304757moz-signature" cols="72">--
Best Regards,
Victor Leschuk | Software Engineer | Access Softek</pre>
</div>
</div>
</div>
</blockquote>
</div>
<br>
</div>
</blockquote>
<br>
<pre class="m_-7612381275907462952moz-signature" cols="72">--
Best Regards,
Victor Leschuk | Software Engineer | Access Softek</pre>
</div></div></div>
</blockquote></div><br></div>