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<body><span class="vcard"><a class="email" href="mailto:dblaikie@gmail.com" title="David Blaikie <dblaikie@gmail.com>"> <span class="fn">David Blaikie</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - Constexpr new: uncatched UB in constant context"
href="https://bugs.llvm.org/show_bug.cgi?id=43685">bug 43685</a>
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<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
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<td style="text-align:right;">Resolution</td>
<td>---
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<td>INVALID
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<td style="text-align:right;">Status</td>
<td>NEW
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<td>RESOLVED
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - Constexpr new: uncatched UB in constant context"
href="https://bugs.llvm.org/show_bug.cgi?id=43685#c4">Comment # 4</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - Constexpr new: uncatched UB in constant context"
href="https://bugs.llvm.org/show_bug.cgi?id=43685">bug 43685</a>
from <span class="vcard"><a class="email" href="mailto:dblaikie@gmail.com" title="David Blaikie <dblaikie@gmail.com>"> <span class="fn">David Blaikie</span></a>
</span></b>
<pre>(In reply to Alexander Zaitsev from <a href="show_bug.cgi?id=43685#c3">comment #3</a>)
<span class="quote">> I don't know a lot about internals and how it can be detected (I trust you
> that checking something like that is undetectable). But if it's undefined
> behavior in C++ standard it shall lead to compile error in constexpr (AFAIK
> constexpr context cannot have UB inside and all code with UB shall lead to
> compile error).</span >
So the wording in C++17 is as follows:
8.20 [expr.const] p2
"An expression e is a core constant expression unless the evaluation of e,
following the rules of the abstract machine (4.6), would evaluate one of the
following expressions:"
...
"an operation that would have undefined behavior as specified in Clauses 4
through 19 of this document"
That specifically does not include Clause 20, which is where the standard
library is defined.
So I believe the compiler behavior you're observing is conforming, though the
code is non-portable (as it's /possible/ that some other implementation might
have UB (as specified in Clauses 4 through 19) on these codepaths - but it's
not required that they do).</pre>
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