Relocation (= move+destroy)

[Marc Glisse]

On Sat, 1 Sep 2018, Marc Glisse wrote:

> this patch passed bootstrap+regtest on powerpc64le-unknown-linux-gnu.

I realized afterwards that for a C++17-only feature, that's not testing 
much... So I changed it to apply in C++14 and fixed a minor issue. There 
is now a single regression:

23_containers/vector/modifiers/push_back/49836.cc

The PR was about not using assignment for an operation that should only 
use construction, and that's fine. But we ended up with a stricter 
testcase using CopyConsOnlyType, where the type has a deleted move 
constructor which, as far as I understand the standard, makes it an 
invalid type for use in vector::push_back. Is that something we want to 
keep supporting, or may I break it? What is happening is that the 
definition of __use_relocate asks if some expression involving a move of 
_Tp is noexcept, which causes a hard error. It would certainly be possible 
to work around that, but it would complicate the code and seems quite 
pointless to me.

-- 
Marc Glisse
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