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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. -O2)"
href="https://bugs.llvm.org/show_bug.cgi?id=51140">51140</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>missed optimization for dead code elimination at -O3 (vs. -O2)
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</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>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>theodoros.theodoridis@inf.ethz.ch
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>$./bin/clang -v
clang version 13.0.0 (<a href="https://github.com/llvm/llvm-project.git">https://github.com/llvm/llvm-project.git</a>
96d8f2a1e0842b83b319a8daf3cc82dd5e1350fa)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /dev/shm/llvm-project/build/./bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
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
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Selected multilib: .;@m64
$cat test.c
extern void foo(void);
extern void bar(void);
int a, b;
int main() {
int c;
unsigned d = 0;
for (; d < 2; d++)
while (a)
for (c = -11; c < 21; c++) {
b = 1 - d;
if (!b)
foo();
bar();
}
return 0;
}
$./bin/clang -O2 test.c -S -o O2.s
$./bin/clang -O3 test.c -S -o O3.s
$grep foo O2.s
$grep foo O3.s
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo
callq foo</pre>
</div>
</p>
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