[committed] libstdc++: Reduce header dependencies for C++20 std::erase [PR92546]

[Jonathan Wakely]

On Sat, 2 Oct 2021, 13:02 François Dumont via Libstdc++, <
libstdc++@gcc.gnu.org> wrote:

> On 01/10/21 9:38 pm, Jonathan Wakely via Libstdc++ wrote:
> > This reduces the preprocessed size of <deque>, <string> and <vector> by
> > not including <bits/stl_algo.h> for std::remove and std::remove_if.
> >
> > Also unwrap iterators using __niter_base, to avoid redundant debug mode
> > checks.
>
> I don't know if you noticed but the __niter_base is a no-op here.
>

Oh, I didn't notice.


> __niter_base unwrap only random access iterators because it is the only
> category for which we know that we have been able to confirm validity or
> not.
>

But these are all random access. I must be missing something.


> We would need to introduce another function to do this or specialize in
> some way erase_if for debug containers. I'll try to find a solution.
>

OK, thanks. Maybe we can just leave the checking there. I wanted to avoid
the overhead because we know that the iterator range is valid. Any checks
done on each increment and equality comparison are wasteful, as they will
never fail.




>
> >
> >       PR libstdc++/92546
> >       * include/bits/erase_if.h (__erase_nodes_if): Use __niter_base to
> >       unwrap debug iterators.
> >       * include/bits/refwrap.h: Do not error if included in C++03.
> >       * include/bits/stl_algo.h (__remove_if): Move to ...
> >       * include/bits/stl_algobase.h (__remove_if): ... here.
> >       * include/std/deque (erase, erase_if): Use __remove_if instead of
> >       remove and remove_if.
> >       * include/std/string (erase, erase_if): Likewise.
> >       * include/std/vector (erase, erase_if): Likewise.
> >
> > Tested powerpc64le-linux. Committed to trunk.
> >
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