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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missing diagnostic for comma in constant expression"
href="https://bugs.llvm.org/show_bug.cgi?id=50342">50342</a>
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<th>Summary</th>
<td>Missing diagnostic for comma in constant expression
</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>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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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>john.brawn@arm.com
</td>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>In the C11 (and earlier) standard it says in section 6.6 about constant
expressions:
Constant expressions shall not contain assignment, increment, decrement,
function-call,
or comma operators, except when they are contained within a subexpression
that is not
evaluated.
Which means we should be giving a diagnostic for code like this
static const int i = 0 ? 2 : ((void)3, 4);
There's a comment in clang/lib/Sema/SemaDecl.cpp about this:
// FIXME: Need strict checking. In C89, we need to check for
// any assignment, increment, decrement, function-calls, or
// commas outside of a sizeof. In C99, it's the same list,
// except that the aforementioned are allowed in unevaluated
// expressions. Everything else falls under the
// "may accept other forms of constant expressions" exception.</pre>
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