[cfe-dev] [libcxx] Removing _LIBCPP_TRIVIAL_PAIR_COPY_CTOR option.

[Dimitry Andric via cfe-dev]

We still turn off, and have always turned off, the _LIBCPP_TRIVIAL_PAIR_COPY_CTOR option in FreeBSD, since we are supposed to be backwards compatible with previous versions of libc++ that we shipped; see https://svnweb.freebsd.org/base/head/contrib/libc++/include/__config?view=markup#l733 <https://svnweb.freebsd.org/base/head/contrib/libc++/include/__config?view=markup#l733>

If the option is completely removed, we will either have to supply two versions of libc++, or bolt on some sort of backwards compatibility versioned symbols.  Alternatively, we can add a local hack to put back the non-trivial copy constructor, but that might lead to other headaches.

David, do you have any good ideas for this?  I think your idea was to burn all backwards compatibility bridges, but we can't really do that for FreeBSD 11.0 at this point, so we would have to start backporting fixes from trunk libc++, instead of importing it wholesale.  For FreeBSD 12.0 we could ship only the new libc++, and provide the older libc++ as a compatibility package.

-Dimitry

> On 14 Jun 2016, at 03:44, Eric Fiselier via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> 
> I have removed this option from in the libc++ in r272613.  I believe it has no clients.
> If anybody uses this option please contact me.
> 
> This option was used to turn off std::pair's trivial copy constructor, instead selecting an older non-trivial implementation.
> 
> It was added in r194742, on November 14th 2013. At that time Apple platforms used this option to turn off pairs trivial constructor. Two weeks later, on November 26th 2013, the default value for Apple platforms was removed in r195796.
> 
> Defining `_LIBCPP_TRIVIAL_PAIR_COPY_CTOR` will now cause an explicit error informing the client that the option has been removed. I will remove this diagnostic after the 3.9 release.
> 
> /Eric
> 
> 
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