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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - false positive in for-loop: static analyzer iterates too often"
href="https://llvm.org/bugs/show_bug.cgi?id=24688">24688</a>
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<th>Summary</th>
<td>false positive in for-loop: static analyzer iterates too often
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>3.7
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Static Analyzer
</td>
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<th>Assignee</th>
<td>kremenek@apple.com
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<th>Reporter</th>
<td>stephan.beyer@uni-osnabrueck.de
</td>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>Hi,
consider the following C++ minimal example:
#include <iostream>
#include <cassert>
int main(int argc, const char *argv[])
{
int my_array[4] = {0, 1, 2, 3};
assert(argc < 3);
for (int i = 0; i < 2*argc; i += 2) {
std::cout << my_array[i] << std::endl;
}
return 0;
}
Clearly, it will output 0 when calling with no argument, and it will output 0
and 2 when calling with one argument.
However, the analyzer says:
minimal.cc:9:9: warning: Function call argument is an uninitialized value
std::cout << my_array[i] << std::endl;
^~~~~~~~~~~~~~~~~~~~~~~~
and the report says that this is because the loop condition is true for *3*
times. Which cannot be the case due to the assertion.
Note that replacing the for-loop by the equivalent
for (int i = 0; i < argc; i++) {
std::cout << my_array[2*i] << std::endl;
}
gets rid of the false positive.
I can reproduce it with Debian's clang++-3.5, 3.7 and 3.8.
Stephan</pre>
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