<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Compiling with -O1 is slower than -O2"
href="https://bugs.llvm.org/show_bug.cgi?id=43084">43084</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Compiling with -O1 is slower than -O2
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.4
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>hehaochen13@nudt.edu.cn
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=22412" name="attach_22412" title="from clangBug-14651">attachment 22412</a> <a href="attachment.cgi?id=22412&action=edit" title="from clangBug-14651">[details]</a></span>
from clangBug-14651
See the following results:
##### This is normal #####
-- clang version 3.4.2 --(CentOS Linux release 7.6.1810 Core)
time clang++ -O0 -w tramp3d-v4.cpp 5.951s
time clang++ -O1 -w tramp3d-v4.cpp 9.890s
time clang++ -O2 -w tramp3d-v4.cpp 12.931s
time clang++ -O3 -w tramp3d-v4.cpp 14.078s
time clang++ -Os -w tramp3d-v4.cpp 11.100s
time clang++ -Ofast -w tramp3d-v4.cpp 14.107s
##### This is normal #####
-- Apple clang version 11.0.0 (clang-1100.0.20.17) --(MacOS Mojave 10.14.6)
time clang -DHC4 -DSAFETY -DNOREDUCE -DNFAIR=3 -O0 -o files pan.c 1.176s
time clang -DHC4 -DSAFETY -DNOREDUCE -DNFAIR=3 -O1 -o files pan.c 12.805s
time clang -DHC4 -DSAFETY -DNOREDUCE -DNFAIR=3 -O2 -o files pan.c 20.955s
time clang -DHC4 -DSAFETY -DNOREDUCE -DNFAIR=3 -O3 -o files pan.c 20.907s
time clang -DHC4 -DSAFETY -DNOREDUCE -DNFAIR=3 -Os -o files pan.c 17.487s
time clang -DHC4 -DSAFETY -DNOREDUCE -DNFAIR=3 -Ofast -o files pan.c 20.362s
##### This is NOT normal #####
-- clang version 3.4.2 --(CentOS Linux release 7.6.1810 Core)
time clang -DHC4 -DSAFETY -DNOREDUCE -DNFAIR=3 -O0 -o files pan.c 1.440s
time clang -DHC4 -DSAFETY -DNOREDUCE -DNFAIR=3 -O1 -o files pan.c 37.666s //
This is NOT normal
time clang -DHC4 -DSAFETY -DNOREDUCE -DNFAIR=3 -O2 -o files pan.c 26.200s
time clang -DHC4 -DSAFETY -DNOREDUCE -DNFAIR=3 -O3 -o files pan.c 26.780s
time clang -DHC4 -DSAFETY -DNOREDUCE -DNFAIR=3 -Os -o files pan.c 18.114s
time clang -DHC4 -DSAFETY -DNOREDUCE -DNFAIR=3 -Ofast -o files pan.c 26.185s
pan.c is from clang-14651(<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED DUPLICATE - CLANG Compilation 4x Slower Than GCC"
href="show_bug.cgi?id=14651">https://bugs.llvm.org/show_bug.cgi?id=14651</a>), while
tramp3d-v4 is an open source benchmark.
As described in the GCC documentation: "-O2 turns on all optimization flags
specified by -O1 and it also turns on the following optimization flags: xxx,
xxx..."(and I think it is similar in
clang(<a href="https://stackoverflow.com/questions/15548023/clang-optimization-levels">https://stackoverflow.com/questions/15548023/clang-optimization-levels</a>))
So I think compiling with -O1 are not expected to be slower than that with -O2.
So I think this may be a performance bug.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>