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Date: Thu, 28 May 2015 13:52:00 -0000
From: Jonathan Wakely <jwakely@redhat.com>
To: libstdc++@gcc.gnu.org
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [patch] libstdc++/65352 fix ubsan errors in std::array<T, 0>
Message-ID: <20150528133817.GP2985@redhat.com>
References: <20150528115330.GL2985@redhat.com> <alpine.DEB.2.11.1505281522500.11312@stedding.saclay.inria.fr>
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On 28/05/15 15:26 +0200, Marc Glisse wrote:
>On Thu, 28 May 2015, Jonathan Wakely wrote:
>
>>Unsurprisingly ubsan doesn't like referencing a null pointer.
>>
>>With this change __array_traits::_S_ref is only used to access an
>>element, which is invalid for std::array<T, 0> anyway.
>
>Should
>
>return *static_cast<_Tp*>(nullptr);
>
>be replaced with
>
>__builtin_unreachable();
>
>then? It seems strange to keep an implementation that is never 
>supposed to be used.

That's a good idea, I experimented with just not defining it but that
fails for explicit instantiations of array<T, 0>.