<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Clang miscompiles with -O0."
href="https://bugs.llvm.org/show_bug.cgi?id=37115">37115</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Clang miscompiles with -O0.
</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>Windows NT
</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>Vsevolod.Livinskij@frtk.ru
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Clang miscompiles testcase with -O0.
Reproducer:
<span class="quote">>$ cat repr.cpp</span >
#include <stdio.h>
struct struct_1 {
int a : 17;
bool b;
static int stat_memb;
};
int struct_1::stat_memb;
struct_1 struct_obj_1 = {42, false};
struct_1 struct_obj_2 = {42, false};
int var;
void tf_3_foo() {
struct_obj_2.stat_memb = unsigned(~0) > 0;
var = -((-9223372036854775807L - 1) * struct_obj_1.stat_memb /
(-9223372036854775807L - 1)) * struct_obj_1.a;
}
int main() {
tf_3_foo();
printf("%d\n", var);
}
Error:
<span class="quote">>$ clang++ -O0 repr.cpp ; ./a.out</span >
42
<span class="quote">>$ clang++ -O1 repr.cpp ; ./a.out</span >
-42
GCC also gives -42 as an answer.
LLVM version:
<span class="quote">>$ clang++ -v</span >
clang version 7.0.0 (trunk 329789)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /llvm/bin-trunk/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>