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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=49775">49775</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>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>[582] % clangtk -v
clang version 13.0.0 (<a href="https://github.com/llvm/llvm-project.git">https://github.com/llvm/llvm-project.git</a>
9fb0025f7084db14d16fe5cbe1d799f4ee0020af)
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
[583] %
[583] % clangtk -O2 -S -o O2.s small.c
[584] % clangtk -O3 -S -o O3.s small.c
[585] %
[585] % wc O2.s O3.s
32 76 770 O2.s
147 415 2958 O3.s
179 491 3728 total
[586] %
[586] % grep foo O2.s
[587] % grep foo O3.s
callq foo
[588] %
[588] % cat small.c
extern void foo(void);
static int b, c, *d = &b, *e = &b;
char *f;
int h;
static void g() { b = h; }
int main() {
int i = 0;
while (i < 2)
i++;
if (!(i ^ *e)) {
foo();
g();
for (c = 0; c < 50; c++)
*f = 0;
}
*d = 0;
}</pre>
</div>
</p>
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