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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Regression: Miscompile with -O1 and -fsanitize=signed-integer-overflow"
href="https://llvm.org/bugs/show_bug.cgi?id=23212">23212</a>
</td>
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<th>Summary</th>
<td>Regression: Miscompile with -O1 and -fsanitize=signed-integer-overflow
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Macintosh
</td>
</tr>
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<th>OS</th>
<td>MacOS X
</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>LLVM Codegen
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>jonathan.sauer@gmx.de
</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>The following program should print 1, and it does so when compiled with clang
r234732 and either -O1 or -fsanitize=signed-integer-overflow. However, when
compiled with both -O1 *and* -fsanitize=signed-integer-overflow, it prints 0.
#include <cstdio>
int flipSign(unsigned int t)
{
return -int(t);
}
int main()
{
std::printf("%d\n", -2 == flipSign(2));
}
% ~/LLVM/build/Release+Asserts/bin/clang++ -O1 clang.cpp && ./a.out
1
% ~/LLVM/build/Release+Asserts/bin/clang++ -fsanitize=signed-integer-overflow
clang.cpp && ./a.out
1
% ~/LLVM/build/Release+Asserts/bin/clang++ -O1
-fsanitize=signed-integer-overflow clang.cpp && ./a.out
0
When compiled with clang r234147, it always prints 1. So does removing the
explicit cast to "int" in "flipSign".
The miscompile also happens with higher optimization levels, e.g. -O2, -O3 and
-Os.
Detailed clang version:
clang version 3.7.0 (trunk 234732)
Target: x86_64-apple-darwin13.4.0
Thread model: posix</pre>
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