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<div class="moz-cite-prefix">On 3/1/17 6:58 PM, Peizhao Ou wrote:<br>
</div>
<blockquote
cite="mid:CAAQDmoL3TpRdcXNNksEofsX91J_nC359R=DY8uiUpuLeCtb3_w@mail.gmail.com"
type="cite">
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<div dir="ltr">Yeah, it looks like SROA does mem2reg too. One more
update is that the following two combinations are fine:
<div>1. opt (no optimization) + llc (-O0)</div>
<div>2. opt (-O3) + llc (-O3)</div>
<div><br>
</div>
<div>And the problematic combination is "opt (-O3) + llc (-O0)".
Now I suspect that there are even synergistic effects between
frontend and backend optimizations. Any comments about that?</div>
</div>
</blockquote>
<br>
There are passes like UnifyExitNodes that some passes may assume
have already been executed. That could trigger a misoptimization.<br>
<br>
That said, I would really like to see bugpoint try to reduce this
bug. Your situation is a perfect case for bugpoint, and bugpoint
should be able to reduce the optimizations and code down to a point
where someone can tell whether it's a missing optimization or a bug
in an optimization.<br>
<br>
Regards,<br>
<br>
John Criswell<br>
<br>
<blockquote
cite="mid:CAAQDmoL3TpRdcXNNksEofsX91J_nC359R=DY8uiUpuLeCtb3_w@mail.gmail.com"
type="cite">
<div dir="ltr">
<div><br>
</div>
<div>Thanks,</div>
<div>Peizhao</div>
<div><a moz-do-not-send="true"
href="http://plrg.eecs.uci.edu/%7Epeizhaoo/profile/">http://plrg.eecs.uci.edu/~peizhaoo/profile/</a> </div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, Mar 1, 2017 at 2:35 PM, Sean
Silva <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:chisophugis@gmail.com" target="_blank">chisophugis@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote">
<div dir="ltr"><br>
<div class="gmail_extra"><br>
<div class="gmail_quote"><span class="">On Wed, Mar 1,
2017 at 12:53 PM, John Criswell via llvm-dev <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:llvm-dev@lists.llvm.org"
target="_blank">llvm-dev@lists.llvm.org</a>></span>
wrote:<br>
<blockquote class="gmail_quote">
<div><span>
<div
class="m_627183699730871673m_-943774855540209988moz-cite-prefix">On
3/1/17 2:54 PM, Peizhao Ou via llvm-dev
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hi everyone,
<div><br>
</div>
<div>I am currently testing out a
combination of IR->IR passes with opt
to benchmark how they affect
performance. The source code works fine
if simply use the clang (-O0/-O3) to
directly compile to object files and
link them. However, when I use opt with
a select set of passes and then use llc
to compile them to binary, the compiled
binary is wrong.</div>
</div>
</blockquote>
<br>
</span> Can you clarify what you mean by "binary
is wrong"? Does the program not link, or does
it produce incorrect results when executed?<br>
<br>
You might try running mem2reg before any other
passes in your random list of optimizations.
mem2reg does SSA construction; I'd bet that
you're more likely to trigger a bug in other
passes if you haven't run mem2reg first. That
said, I don't think any passes are needed for
correctness.<br>
</div>
</blockquote>
<div><br>
</div>
</span>
<div>SROA does this too (among other things).</div>
<span class="HOEnZb">
<div><br>
</div>
<div>-- Sean Silva</div>
</span>
<div>
<div class="h5">
<div> </div>
<blockquote class="gmail_quote">
<div> <br>
You might also try using bugpoint to reduce
the bug that you're seeing. As I said before,
you may be triggering bugs that don't usually
show up in the standard pass pipeline.
Reducing the bug (and fixing it if you are
willing and able) would help improve the
quality of the code.<br>
<br>
Regards,<br>
<br>
John Criswell<br>
<br>
<br>
<blockquote type="cite"><span>
<div dir="ltr">
<div><br>
</div>
<div>That makes me wonder if there are
any IR->IR passes that are
indispensable and they are to
guarantee the semantics?</div>
<div><br>
</div>
<div>Here's my workflow just in case:<br>
</div>
<div>******************************<wbr>******************************<wbr>*********************</div>
<div>1. Compile the source code to
unoptimized IRs:</div>
<div>clang -c -emit-llvm -O0 test.c -o
test.bc</div>
<div>2. Run opt with a set of IR->IR
passes, e.g.,</div>
<div>opt -simplifycfg -sroa -inferattrs
-globalopt -instcombine -simplifycfg
-prune-eh -inline -tailcallelim
-simplifycfg -loop-simplify -lcssa
-loop-rotate -licm -gvn -verify
test.bc -o test.bc</div>
<div>3. Run llc with -O0:</div>
<div>llc -file-type=obj test.bc -o
test.o</div>
<div>4. Last link all the object files:</div>
<div>clang -O0 test1.o test2.o -o test</div>
<div>******************************<wbr>******************************<wbr>*********************<br>
</div>
<div><br>
</div>
<div>Thanks,</div>
<div>Peizhao</div>
<div><br>
</div>
</div>
<br>
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<pre class="m_627183699730871673m_-943774855540209988moz-signature" cols="72">--
John Criswell
Assistant Professor
Department of Computer Science, University of Rochester
<a moz-do-not-send="true" class="m_627183699730871673m_-943774855540209988moz-txt-link-freetext" href="http://www.cs.rochester.edu/u/criswell" target="_blank">http://www.cs.rochester.edu/u/<wbr>criswell</a></pre>
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<p>
</p><pre class="moz-signature" cols="72">--
John Criswell
Assistant Professor
Department of Computer Science, University of Rochester
<a class="moz-txt-link-freetext" href="http://www.cs.rochester.edu/u/criswell">http://www.cs.rochester.edu/u/criswell</a></pre></body></html>