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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 --- - Clang miscompiles the code with loop unrolling (-m32/-O2)"
href="http://llvm.org/bugs/show_bug.cgi?id=19291">19291</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Clang miscompiles the code with loop unrolling (-m32/-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>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>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>samsonov@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>eugeni.stepanov@gmail.com, llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Reproduces with trunk Clang for me:
$ cat test.cc
#include <stdio.h>
#include <stdlib.h>
#include <vector>
using namespace std;
template <unsigned long bvsize>
void Test() {
vector<unsigned long> bits(bvsize);
for (unsigned long it = 0; it < 30; it++) {
for (unsigned long j = 0; j < bits.size(); j++) {
bits[j] = j;
}
for (size_t j = 0; j < bits.size(); j++) {
if (j != bits[j]) {
fprintf(stderr, "%zu:%lu\n", j, bits[j]);
abort();
}
}
}
}
int main(int argc, char **argv) {
Test<8>();
Test<16>();
Test<32>();
Test<64>();
return 0;
}
$ bin/clang -fPIC -O2 -m32 -lstdc++ test.cc && ./a.out
0:980777509
Aborted (core dumped)
The problem goes away if I remove -fPIC or -m32, or reduce the number of Test<>
instantiations.</pre>
</div>
</p>
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