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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Regression: -Wnull-dereference (part of -Wall) even applies to expressions that are not evaluated."
href="https://llvm.org/bugs/show_bug.cgi?id=26398">26398</a>
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<th>Summary</th>
<td>Regression: -Wnull-dereference (part of -Wall) even applies to expressions that are not evaluated.
</td>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.8
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>other
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>release blocker
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Frontend
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>ed@80386.nl
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>I just upgraded from LLVM+Clang 3.7.1 to LLVM+Clang 3.8.0rc1 and I noticed that
the following code now generates a compiler warning/error:
$ cat bla.c
#define some_generic_function(x) \
_Generic(*(x), \
int: some_generic_function_int)(x)
static int *some_generic_function_int(int *x) {
return x;
}
void some_function(void);
void some_function(void) {
some_generic_function((int *)0);
}
$ x86_64-unknown-cloudabi-cc -O3 -Wall -Werror bla.c
bla.c:11:3: error: indirection of non-volatile null pointer will be deleted,
not trap [-Werror,-Wnull-dereference]
some_generic_function((int *)0);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bla.c:2:14: note: expanded from macro 'some_generic_function'
_Generic(*(x), \
^~~~
bla.c:11:3: note: consider using __builtin_trap() or qualifying pointer with
'volatile'
bla.c:2:14: note: expanded from macro 'some_generic_function'
_Generic(*(x), \
^
1 error generated.
The warning should obviously not trigger in this case; the expression passed to
_Generic() is not evaluated. This is also not an uncommon construct. With
_Generic() you often want to match a type without any cv-qualifiers on the
pointer type. Dereferencing the expression is an easy way to get rid of those.</pre>
</div>
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