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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - missed optimization for dead code elimination at -O3 (vs. -O1)"
href="https://bugs.llvm.org/show_bug.cgi?id=49731">49731</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>missed optimization for dead code elimination at -O3 (vs. -O1)
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Interprocedural Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>zhendong.su@inf.ethz.ch
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>[654] % clangtk -v
clang version 13.0.0 (<a href="https://github.com/llvm/llvm-project.git">https://github.com/llvm/llvm-project.git</a>
dc46783f7f61f54618b4cf1b0b325fdad304d109)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /local/suz-local/opfuzz/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
[655] %
[655] % clangtk -O1 -S -o O1.s small.c
[656] % clangtk -O3 -S -o O3.s small.c
[657] %
[657] % wc O1.s O3.s
17 45 546 O1.s
46 140 1298 O3.s
63 185 1844 total
[658] %
[658] % grep foo O1.s
[659] % grep foo O3.s
callq foo
[660] %
[660] % cat small.c
extern void foo(void);
static long a = 78240;
static int b, d;
static short e;
static short c(short f, short h) { return h == 0 || (f && h == 1) ? 0 : f % h;
}
int main() {
short g = a;
for (b = 0; b < 1; b++) {
e = a;
d = c((e == a) ^ g, a);
}
if (d) {
foo();
for (; a; a++)
;
}
return 0;
}</pre>
</div>
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