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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - clang miscompiles at -O2 and above on valid code"
href="https://bugs.llvm.org/show_bug.cgi?id=38125">38125</a>
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</tr>
<tr>
<th>Summary</th>
<td>clang miscompiles at -O2 and above on valid code
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</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>LLVM Codegen
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>helloqirun@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>It seems to be a recent regression.
$ clang-trunk -v
clang version 7.0.0 (trunk 336646)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
$ clang-trunk abc.c ; ./a.out
0
FFFFFFFA
$ clang-trunk -O2 abc.c ; ./a.out
0
5
$ cat abc.c
int printf(char *, ...);
int a, c;
unsigned short b;
short d;
void fn1(char p1) { a = a ^ p1; }
void fn2(long p1) {
a = p1 & 5;
fn1(p1 >> 56);
}
int main() {
for (; c >= 0; c--)
d = -3L;
d |= b;
fn2(d);
printf("%d\n", b);
printf("%X\n", a);
}</pre>
</div>
</p>
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