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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Not a constant expression: comparison between unequal pointers to void has unspecified result"
href="https://bugs.llvm.org/show_bug.cgi?id=46308">46308</a>
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<th>Summary</th>
<td>Not a constant expression: comparison between unequal pointers to void has unspecified result
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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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>
</tr>
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<th>Keywords</th>
<td>compile-fail
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++14
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>language.lawyer@gmail.com
</td>
</tr>
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<th>CC</th>
<td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<p>
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<pre>About the following program:
struct S
{
int i;
int j;
};
constexpr S s {};
static_assert(&s.i < (void*)&s.j);
clang in C++14, C++17 and C++2a modes says that the expression in static_assert
is not a constant expression:
$ clang++ prog.cc -std=c++14
prog.cc:9:15: error: static_assert expression is not an integral constant
expression
static_assert(&s.i < (void*)&s.j, "");
^~~~~~~~~~~~~~~~~~
prog.cc:9:20: note: comparison between unequal pointers to void has unspecified
result
static_assert(&s.i < (void*)&s.j, "");
^
(<a href="https://wandbox.org/permlink/IXwrV0M75To3wUUB">https://wandbox.org/permlink/IXwrV0M75To3wUUB</a>)
However, the special handling of pointers to void has been removed from
[expr.rel] by <a href="http://wg21.link/n3624">http://wg21.link/n3624</a> (applied in [1]), so the result of
comparing unequal pointers to void is no longer unspecified, so the expression
is a constant expression.
[1]
<a href="https://github.com/cplusplus/draft/commit/89281b5795f47b9196c37ce8008b4873a76e90ef#diff-64a673ab7a20068092a4cf86b36f4334L3647-L3650">https://github.com/cplusplus/draft/commit/89281b5795f47b9196c37ce8008b4873a76e90ef#diff-64a673ab7a20068092a4cf86b36f4334L3647-L3650</a></pre>
</div>
</p>
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