libstdc++: Reduce template instantiations in <mdspan>.

In mdspan related code involving static extents, often the IndexType is
part of the template parameters, even though it's not needed.

This commit extracts the parts of _ExtentsStorage not related to
IndexType into a separate class _StaticExtents.

It also prefers passing the array of static extents, instead of the
whole extents object where possible.

The size of an object file compiled with -O2 that instantiates
  Layout::mapping<extents<IndexType, Indices...>::stride
  Layout::mapping<extents<IndexType, Indices...>::required_span_size
for the product of
  - eight IndexTypes
  - three Layouts,
  - nine choices of Indices...
decreases by 19% from 69.2kB to 55.8kB.

libstdc++-v3/ChangeLog:

	* include/std/mdspan (__mdspan::_StaticExtents): Extract non IndexType
	related code from _ExtentsStorage.
	(__mdspan::_ExtentsStorage): Use _StaticExtents.
	(__mdspan::__static_extents): Return reference to NTTP of _StaticExtents.
	(__mdspan::__contains_zero): New overload.
	(__mdspan::__exts_prod, __mdspan::__static_quotient): Use span to avoid
	copying __sta_exts.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
Signed-off-by: Luc Grosheintz <luc.grosheintz@gmail.com>

0 files changed, 0 insertions, 0 deletions