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<body><span class="vcard"><a class="email" href="mailto:richard-llvm@metafoo.co.uk" title="Richard Smith <richard-llvm@metafoo.co.uk>"> <span class="fn">Richard Smith</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - variable-sized object check seems to be too restrictive"
href="http://llvm.org/bugs/show_bug.cgi?id=17818">bug 17818</a>
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<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>NEW
</td>
<td>RESOLVED
</td>
</tr>
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<td style="text-align:right;">CC</td>
<td>
</td>
<td>richard-llvm@metafoo.co.uk
</td>
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<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>INVALID
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - variable-sized object check seems to be too restrictive"
href="http://llvm.org/bugs/show_bug.cgi?id=17818#c1">Comment # 1</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - variable-sized object check seems to be too restrictive"
href="http://llvm.org/bugs/show_bug.cgi?id=17818">bug 17818</a>
from <span class="vcard"><a class="email" href="mailto:richard-llvm@metafoo.co.uk" title="Richard Smith <richard-llvm@metafoo.co.uk>"> <span class="fn">Richard Smith</span></a>
</span></b>
<pre>These are both VLAs. With a slightly different testcase:
C c1;
C *c2 = new C;
int a[c1.asize], b[c2->asize];
... and -pedantic-errors, we see:
<stdin>:9:9: error: variable length array folded to constant array as an
extension [-Werror,-Wgnu-folding-constant]
int a[c1.asize], b[c2->asize];
^~~~~~~~
<stdin>:9:21: error: variable length arrays are a C99 feature
[-Werror,-Wvla-extension]
int a[c1.asize], b[c2->asize];
^
Note that Clang is happy to fold the first case to a constant, and treat it as
not-a-VLA (and indeed, the first *is* a constant expression in C++11 onwards),
but is not happy to do the same for the second case. That's because 'c2->asize'
is defined to mean '(*c2).asize', and while we can evaluate the '.asize' part,
the '(*c2)' is non-constant, because it involves reading the value of 'c2'.
Finally, g++ allows a VLA to have an initializer, whereas Clang does not, so
Clang rejects the second example.</pre>
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