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<p>Hi Philip,<o:p></o:p></p>
<p>Thanks for your kind reply.<o:p></o:p></p>
<p>> A) Are you measuring on tip of tree?� There were changes for multiple exit unrolling which landed very recently.<o:p></o:p></p>
<p>Yep, I am investigating benchmarks with llvm tip and I can see the llvm fails to unroll some loops with multiple exits.<o:p></o:p></p>
<p class="MsoNormal">> B) One of your exits does not dominate your latch.� Those are generally hard<o:p></o:p></p>
<p class="MsoNormal">> C) This example does not seem to require gotos.� I strongly suggest reducing your test cases if you want more informed commentary.�<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I am looking at perlbench recently and it has `goto` statements inside loop. The example is a reduced case. When I look at the gcc’s output of the example, it looks like gcc unrolls only the below `if` statement block…<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> if (*s++ != '\n')<o:p></o:p></p>
<p class="MsoNormal"> continue;<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks<o:p></o:p></p>
<p class="MsoNormal">JinGu Kang<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> <b>On Behalf Of
</b>Philip Reames via llvm-dev<br>
<b>Sent:</b> 16 July 2021 15:52<br>
<b>To:</b> Jingu Kang <Jingu.Kang@arm.com>; llvm-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm-dev] Question about Unrolling Loop with Multiple Exits<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p>A) Are you measuring on tip of tree?� There were changes for multiple exit unrolling which landed very recently.<o:p></o:p></p>
<p>B) One of your exits does not dominate your latch.� Those are generally hard.�
<o:p></o:p></p>
<p>C) This example does not seem to require gotos.� I strongly suggest reducing your test cases if you want more informed commentary.�
<o:p></o:p></p>
<p>Philip<o:p></o:p></p>
<div>
<p class="MsoNormal">On 7/16/21 7:42 AM, Jingu Kang via llvm-dev wrote:<o:p></o:p></p>
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<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal">Hi All,<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">While I am investigating benchmarks, I have found loops which llvm fails to unroll because the loops have multiple exits.<o:p></o:p></p>
<p class="MsoNormal">For example, <o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">char *foo(void);<o:p></o:p></p>
<p class="MsoNormal">int boo(char *s);<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">int test(char *s, char *end, char *check1, char *check2) {<o:p></o:p></p>
<p class="MsoNormal">� while (s <= end) {<o:p></o:p></p>
<p class="MsoNormal">��� if (*s++ != '\n')<o:p></o:p></p>
<p class="MsoNormal">����� continue;<o:p></o:p></p>
<p class="MsoNormal">��� if (check1 || check2) {<o:p></o:p></p>
<p class="MsoNormal">����� s = foo();<o:p></o:p></p>
<p class="MsoNormal">����� if (!s)<o:p></o:p></p>
<p class="MsoNormal">������� goto ret1;<o:p></o:p></p>
<p class="MsoNormal">��� }�� <o:p></o:p></p>
<p class="MsoNormal">����if (boo(s))<o:p></o:p></p>
<p class="MsoNormal">����� goto ret0;<o:p></o:p></p>
<p class="MsoNormal">� }<o:p></o:p></p>
<p class="MsoNormal">� goto ret1;<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">ret0:<o:p></o:p></p>
<p class="MsoNormal">� return 0;<o:p></o:p></p>
<p class="MsoNormal">ret1:<o:p></o:p></p>
<p class="MsoNormal">� return 1;<o:p></o:p></p>
<p class="MsoNormal">}<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">Above code causes below messages from LoopUnroll pass.<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">Bailout for multi-exit handling when latch exit has >1 predecessor.<o:p></o:p></p>
<p class="MsoNormal">Multiple exit/exiting blocks in loop and multi-exit unrolling not enabled!<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">I can see the option `unroll-runtime-multi-exit` and comments about it. I wonder there are already reviews for the work on phabriactor or some people are working on it.<o:p></o:p></p>
<p class="MsoNormal">If someone knows information about it, please share it.<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">Thanks<o:p></o:p></p>
<p class="MsoNormal">JinGu Kang<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal">�<o:p></o:p></p>
<p class="MsoNormal"><br>
<br>
<o:p></o:p></p>
<pre>_______________________________________________<o:p></o:p></pre>
<pre>LLVM Developers mailing list<o:p></o:p></pre>
<pre><a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a><o:p></o:p></pre>
<pre><a href="https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev">https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><o:p></o:p></pre>
</blockquote>
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