[PATCH v1 0/3] Implement aligned_accessor [P2897R7].

[Luc Grosheintz]

This patch series implements the aligned_accessor paper P2897R7 in three
parts:

  - Implement `is_sufficiently_aligned` which is part of <memory>.
  - Prepare the accessor tests for reuse.
  - Implement aligned_accessor.

A couple of remarks:

  - The paper P2897R7 and spec N5008 don't specify that the aligment
  for is_sufficiently_aligned must be a power of two.

  - The reasoning for why is_sufficiently_aligned isn't constexpr is
  nicely described in the paper.

  - Use of `class` in is_sufficiently_aligned is for consistency within
  that file.

  - The tests create new unsupported tests and expected failures. The
  testsuite doesn't have all that many of those; so there's likely a
  strategy to avoid this. However, I don't know how.

  - These changes are independent of mdspan, but due to the precise
  location of the code it might conflict with the mdspan patch series.

  - I skipped updating `cxxapi-data.csv` for is_sufficiently_aligned
  due to consistency with the rest of the mdspan patches, i.e. there
  will be a bulk update of the file later.

  - Each commit was tested with/without PCH and with/without
  _GLIBCXX_DEBUG filtered by 20_util/is_sufficiently_aligned
  and 23_containers/mdspan.
  The last commit was tested fully with/without PCH. All tests on
  x86_64-linux.

As always I'm happy to reorganize into different commits, if the
grouping doesn't make sense.

Luc Grosheintz (3):
  libstdc++: Implement is_sufficiently_aligned.
  libstdc++: Prepare test code for default_accessor for reuse.
  libstdc++: Implement aligned_accessor from mdspan.

 libstdc++-v3/include/bits/align.h             |  16 ++
 libstdc++-v3/include/bits/version.def         |  18 ++
 libstdc++-v3/include/bits/version.h           |  20 +++
 libstdc++-v3/include/std/mdspan               |  72 ++++++++
 libstdc++-v3/include/std/memory               |   1 +
 libstdc++-v3/src/c++23/std.cc.in              |   4 +-
 .../20_util/is_sufficiently_aligned/1.cc      |  31 ++++
 .../20_util/is_sufficiently_aligned/2.cc      |   7 +
 .../23_containers/mdspan/accessors/aligned.cc |  43 +++++
 .../mdspan/accessors/aligned_ftm.cc           |   6 +
 .../mdspan/accessors/aligned_neg.cc           |  33 ++++
 .../accessors/debug/aligned_access_neg.cc     |  23 +++
 .../accessors/debug/aligned_offset_neg.cc     |  23 +++
 .../23_containers/mdspan/accessors/default.cc |  99 -----------
 .../23_containers/mdspan/accessors/generic.cc | 168 ++++++++++++++++++
 15 files changed, 464 insertions(+), 100 deletions(-)
 create mode 100644 libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/1.cc
 create mode 100644 libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/2.cc
 create mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/accessors/aligned.cc
 create mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/accessors/aligned_ftm.cc
 create mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/accessors/aligned_neg.cc
 create mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/accessors/debug/aligned_access_neg.cc
 create mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/accessors/debug/aligned_offset_neg.cc
 delete mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/accessors/default.cc
 create mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/accessors/generic.cc

-- 
2.49.0