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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - combination of -march=native and -O1/2/3 causes "illegal instruction" error"
href="http://llvm.org/bugs/show_bug.cgi?id=22776">22776</a>
</td>
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<tr>
<th>Summary</th>
<td>combination of -march=native and -O1/2/3 causes "illegal instruction" error
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.6
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<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>
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<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>stbudach@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=13983" name="attach_13983" title="test file to reproduce the error">attachment 13983</a> <a href="attachment.cgi?id=13983&action=edit" title="test file to reproduce the error">[details]</a></span>
test file to reproduce the error
#include <iostream>
#include <string>
#include <random>
std::string generateRandomString(size_t len)
{
std::string alphabet = "ACGT";
std::random_device rd;
std::default_random_engine rng(rd());
std::uniform_int_distribution<int> dist (0, alphabet.size()-1);
std::string randomString;
randomString.reserve(len);
for(size_t i = 0; i < len; ++i)
randomString.push_back(alphabet[dist(rng)]);
return randomString;
}
int main()
{
std::cout << generateRandomString(20) << '\n';
}
When compiling the code with "clang++ -std=c++11 -march=native -O3 -o test
test.cpp" I get no compiler errors, but the binary crashes with an "illegal
instruction". Using -march=native and -O1/2/3 separately works fine, just the
combination triggers the error (with clang++ 3.5 and 3.6 on Ubuntu 14.04).
My CPU is an i3-4000M, and clang recognizes it as -target-cpu core-avx2.</pre>
</div>
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