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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - wrong code by LTO at -O1 (only) on x86_64-linux-gnu (affecting 3.4 and trunk)"
href="http://llvm.org/bugs/show_bug.cgi?id=19891">19891</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>wrong code by LTO at -O1 (only) on x86_64-linux-gnu (affecting 3.4 and trunk)
</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>All
</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>su@cs.ucdavis.edu
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>The current clang trunk and clang 3.4 miscompile the following code when using
LTO at -O1 (only) on x86_64-linux-gnu in both 32-bit and 64-bit modes.
This is a regression from clang 3.3.
$ clang-trunk -v
clang version 3.5.0 (trunk 209780)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.8.1
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.1
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
$
$ clang-trunk -O1 small.c; a.out
1
$ clang-trunk -flto -O0 small.c; a.out
1
$ clang-3.3 -flto -O1 small.c; a.out
1
$
$ clang-trunk -flto -O1 small.c; a.out
0
$ clang-3.4 -flto -O1 small.c; a.out
0
$
--------------------------------
int printf (const char *, ...);
int a = 1, c = 1, d;
volatile int b;
int
fn1 ()
{
for (; d < 1; d++)
a = 0;
if (1 & 1 << b)
for (;;)
{
if (a)
break;
return 0;
}
else
c = 0;
return 1;
}
int
main ()
{
fn1 ();
printf ("%d\n", c);
return 0;
}</pre>
</div>
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