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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - System header warning in /usr/include/math.h"
href="https://bugs.llvm.org/show_bug.cgi?id=35268">35268</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>System header warning in /usr/include/math.h
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>5.0
</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>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Frontend
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>tstellar@redhat.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>How to reproduce:
$ cat isnan.c
#include <math.h>
int main(void)
{
double foo = 1.0;
if (isnan(foo))
return 1;
return 0;
}
$ clang -Wdouble-promotion -o isnan isnan.c
isnan.c:7:13: warning: implicit conversion increases floating-point precision:
'double' to 'long double' [-Wdouble-promotion]
if (isnan(foo))
~~~~~~^~~~
/usr/include/math.h:644:46: note: expanded from macro 'isnan'
# define isnan(x) __MATH_TG ((x), __isnan, (x))
~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
/usr/include/math.h:562:16: note: expanded from macro '__MATH_TG'
: FUNC ## l ARGS)
~~~~~~~~~ ^~~~
1 warning generated.
This is an issue with glibc 2.25 and newer. I spent some time debugging this
and it looks like in lib/Basic/DiagnosticIDs.cpp:471, the isInSystemHeader()
function is returning false, because the SourceLocation points to isnan.c:7.
To make it more clear why there is a warning, here are the relevant parts of
the source after running the preprocessor:
extern int __isnan (double __value) __attribute__ ((__nothrow__ ))
__attribute__ ((__const__));
extern int __isnanf (float __value) __attribute__ ((__nothrow__ ))
__attribute__ ((__const__));
extern int __isnanl (long double __value) __attribute__ ((__nothrow__ ))
__attribute__ ((__const__));
int main(void)
{
double foo = 1.0;
if ((sizeof ((foo)) == sizeof (float) ? __isnanf (foo) : sizeof ((foo)) ==
sizeof (double) ? __isnan (foo) : __isnanl (foo)))
return 1;
return 0;
}</pre>
</div>
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