Re: [boost] [move] GCC bug and aliasing questions

Subject: Re: [boost] [move] GCC bug and aliasing questions
From: Tr3wory (tr3w_at_[hidden])
Date: 2012-06-21 16:56:07

On Thu, Jun 21, 2012 at 9:46 PM, Ion Gaztañaga <igaztanaga_at_[hidden]> wrote:
> El 20/06/2012 19:54, Tr3wory escribió:
>
>> But rv<TYPE>  is derived from TYPE so to me it looks like the two type
>> is compatible, therefore the code didn't violate the strict aliasing
>> rules, so the attribute is not necessary.
>> (BTW can we violate the strict aliasing rules trough static_cast if we
>> don't do any chained conversion trough void*?)
>
>
> It might not break strict aliasing (I'm not an expert) but it is undefined
> behavior to static_cast down a hierarchy to a type that isn't actually the
> type of the object. Boost.Move uses this undefined behavior hole and the GCC
> behavior is fixed with may_alias. I haven't found a better solution.

So if I understand you correctly, we are in the field of undefined
behavior either way.
Did you experience any problem with gcc what you solved with
may_alias, or it's just the materialization of the idea of "better
safe than sorry"?

tr3w