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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW " title="NEW --- - sign-compare warning for == and != are pretty useless" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D24036&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=rDG3YZVqWO_rliD2DPoaZX85yHO-gjXFefVPmAaYLho&s=nBQKw9X_SojUgnX9ho4m-5HMzvztN25cdpyPo6YFgLM&e=">24036</a>
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<th>Summary</th>
<td>sign-compare warning for == and != are pretty useless
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</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>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Frontend
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>daniel.marjamaki@evidente.se
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>I recommend that -Wsign-compare is not written for == and != comparisons.
For relational comparisons the sign makes a direct difference, the result of 'a
<span class="quote">> b' can be different if you do a sign-cast of an operand.</span >
For equality comparisons the sign does not make a direct difference. the result
of 'a == b' is the same even if you sign-cast an operand.
Code example:
void f(signed int a, unsigned int b) {
if (a == b) {}
}
Clang writes this warning:
signcompare.c:3:9: warning: comparison of integers of different signs: 'int'
and 'unsigned int' [-Wsign-compare]
if (a == b) {}
~ ^ ~
In my humble opinion the risk of a bug here is really low.
The proper fix for this is to write:
if (a >= 0 && a == b) {}
However I have seen that this is fixed by a useless cast.
This kind of false positive is indirectly a security problem. People routinely
hide these false positives using casts or changed variable types etc. and that
cause bugs and hides other real warnings.
I believe this bug report is related to:
<a class="bz_bug_link
bz_status_NEW " title="NEW --- - false positive, -Wsign-compare, signed value obviously can't be negative" href="show_bug.cgi?id=24035">https://llvm.org/bugs/show_bug.cgi?id=24035</a></pre>
</div>
</p>
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