On 17/07/25 13:06 -0400, Patrick Palka wrote:
On Thu, 17 Jul 2025, Jonathan Wakely wrote:
On 17/07/25 15:31 +0200, Tomasz Kamiński wrote:
> From: Jonathan Wakely <jwak...@redhat.com>
>
> Implement std::inplace_vector as specified in P0843R14, without follow
> up papers, in particular P3074R7 (trivial unions). In consequence
> inplace_vector<T, N> can be used inside constant evaluations only
> if T is trivial of N is equal to zero.
>
> We provide a separate specialization for inplace_vector<T, 0> to meet
> the requirements of N5008 [inplace.vector.overview] p5. In particular
> objects of such types needs to be empty.
>
> To allow contexpr variable of inplace_vector v, where v.size() <
> v.capacity(),
> we need to guaranteed that all elements of the storage array are
> initialized,
> even ones in range [v.data() + v.size(), v.data() + v.capacity()). This is
> perfomed by _M_init function, that is alled by each constructored. By
> storing
> the array in animous union, we can perform this intialization in constant
> evaluation, avoiding the impact on runtime path.
>
> The size() function conveys the information that _M_size <= _Nm to compiler,
> by calling __builtin_unreachable(). In particular this allows us to
> eliminate
> FP warnings by using _Nm - size() instead of _Nm - _M_size, when computing
> available elements.
>
> However, we still have one -Waggressive-loop-optimizations (to best of our
> knowledge false-positive warning produced in cons/from_range.cc and
> cons/throws.cc. Currently it is pruned using dg-prune-output and tracked by
> PR121143.
>
> The included test cover almost all code paths at runtime, however some
> compile time evaluation test are not yet implemented:
> * operations on range, they depenend on making testsuite_iterators constexpr
> * negative test for invoking operations with preconditions at compile time,
> especially for zero size specialization.
>
> PR libstdc++/119137
>
> libstdc++-v3/ChangeLog:
>
> * doc/doxygen/user.cfg.in (INPUT): Add new header.
> * include/Makefile.am: Add new header.
> * include/Makefile.in: Regenerate.
> * include/bits/version.def (inplace_vector): Define.
> * include/bits/version.h: Regenerate.
> * include/precompiled/stdc++.h: Include new header.
> * src/c++23/std.cc.in: Export contents if new header.
> * include/std/inplace_vector: New file.
> * testsuite/23_containers/inplace_vector/access/capacity.cc: New file.
> * testsuite/23_containers/inplace_vector/access/elem.cc: New file.
> * testsuite/23_containers/inplace_vector/access/elem_neg.cc: New file.
> * testsuite/23_containers/inplace_vector/cons/1.cc: New file.
> * testsuite/23_containers/inplace_vector/cons/from_range.cc: New file.
> * testsuite/23_containers/inplace_vector/cons/throws.cc: New file.
> * testsuite/23_containers/inplace_vector/copy.cc: New file.
> * testsuite/23_containers/inplace_vector/erasure.cc: New file.
> * testsuite/23_containers/inplace_vector/modifiers/assign.cc: New
> file.
> * testsuite/23_containers/inplace_vector/modifiers/erase.cc: New file.
> * testsuite/23_containers/inplace_vector/modifiers/multi_insert.cc:
> New file.
> * testsuite/23_containers/inplace_vector/modifiers/single_insert.cc:
> New file.
> * testsuite/23_containers/inplace_vector/move.cc: New file.
> * testsuite/23_containers/inplace_vector/relops.cc: New file.
> * testsuite/23_containers/inplace_vector/version.cc: New file.
> * testsuite/util/testsuite_iterators.h (input_iterator_wrapper::base):
> Define.
>
> Co-authored-by: Tomasz Kamiński <tkami...@redhat.com>
> Signed-off-by: Tomasz Kamiński <tkami...@redhat.com>
> ---
> Jonathan have provided initial implementation, that I (Tomasz) have
> later finished and extended the test coverate. Details can be found at:
> https://forge.sourceware.org/gcc/gcc-TEST/pulls/58
>
> Tested on x86_64-linux. OK for trunk?
OK for trunk with the typos in the commit msg fixed, and the redundant
header remove that Patrick noticed.
I don't know why Gmail decided to garble my mail by wrapping it to 80 characters
but I also have some other review comments in there.
Oh yes, sorry! I see them now. I'll try to respond in a non-gmail mail
client.
