<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><br></div><div>Thanks,</div><div>Peizhao</div><div><a href="http://plrg.eecs.uci.edu/~peizhaoo/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 href="mailto:chisophugis@gmail.com" target="_blank">chisophugis@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><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 href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"><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"><font color="#888888"><div><br></div><div>-- Sean Silva</div></font></span><div><div class="h5"><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000">
<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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</span></blockquote><span class="m_627183699730871673HOEnZb"><font color="#888888">
<br>
<p><br>
</p>
<pre class="m_627183699730871673m_-943774855540209988moz-signature" cols="72">--
John Criswell
Assistant Professor
Department of Computer Science, University of Rochester
<a 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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