libstdc++: Avoid redundant value_type object in flat_set::emplace [PR119620]

flat_set::emplace (and flat_multiset's) currently unconditionally
constructs an object outside of the container, but if we're passed
a value_type object we can and should avoid that.

	PR libstdc++/119620

libstdc++-v3/ChangeLog:

	* include/std/flat_set (_Flat_set_impl::_M_try_emplace): Split
	out into two overloads, one taking at least one argument and one
	taking zero arguments.  Turn __k into an auto&& reference bound
	to __arg if it's already a value_type and otherwise bound to a
	lifetime-extended value_type temporary.
	* testsuite/23_containers/flat_multiset/1.cc (test08): New test.
	* testsuite/23_containers/flat_set/1.cc (test08): New test.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

0 files changed, 0 insertions, 0 deletions