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On Fri, 26 Oct 2018, Marc Glisse wrote:
Hello,
here are some tweaks so that I can usefully mark deque as trivially
relocatable. It includes more noexcept(auto) madness. For __relocate_a_1, I
should also test if copying, ++ and != are noexcept, but I wanted to ask
first because there might be restrictions on what iterators are allowed to
do, even if I didn't see them. Also, the current code already ignores those,
so it may as well be fixed in another patch.
Allocators are complicated. I specialized only for the default allocator,
because that's by far the one that is used the most, and I have much less
risk of getting it wrong. Some allocator expert is welcome to make a better
test. I do not know in details how deque is implemented. A quick look seemed
to show that trivial relocation should be fine, but I would appreciate a
confirmation.
The extra parameter for __is_trivially_relocatable is not used, but I expect
it will be as soon as the specializations of __is_trivially_relocatable
become more advanced.
If I use or specialize __is_trivially_relocatable in many places, this forces
to #include bits/stl_uninitialized.h in many places. I wonder if I should
move some of that stuff. Since I may use it in std::swap, bits/move.h looks
like a sensible place for the core pieces (__is_trivially_relocatable, and
__relocate_object if I ever create that). That or type_traits.
Regtested on gcc112. I manually checked that there was a speed-up for
operations on vector<deque<int>>, although doing any kind of benchmarking on
gcc112 is hard, I'll test locally next time.
2018-10-26 Marc Glisse <marc.gli...@inria.fr>
PR libstdc++/87106
* include/bits/stl_algobase.h: Include <type_traits>.
(__niter_base): Add noexcept specification.
* include/bits/stl_deque.h: Include <bits/stl_uninitialized.h>.
(__is_trivially_relocatable): Specialize for deque.
* include/bits/stl_iterator.h: Include <type_traits>.
(__niter_base): Add noexcept specification.
* include/bits/stl_uninitialized.h (__is_trivially_relocatable):
Add parameter for meta-programming.
(__relocate_a_1, __relocate_a): Add noexcept specification.
* include/bits/stl_vector.h (__use_relocate): Test __relocate_a.
--
Marc Glisse
