[PATCH] PR libstdc++/80285 optimize std::make_shared for -fno-rtti

[Jonathan Wakely <jwakely at redhat dot com>]

std::make_shared didn't support embedding the object within the
shared_ptr bookkeeping structure when -fno-rtti was used. This was
because the trick I use for getting the address of the embedded
object relied on typeid, so without RTTI it just creating the object
separately on the heap.

This removes the alternative code path for -fno-rtti and simply forms
a fake std::type_info& reference using reinterpret_cast. This allows
us to embed the object and get its address without typeid, so we avoid
the second allocation even when -fno-rtti is used.

	PR libstdc++/80285
	* include/bits/shared_ptr_base.h (_Sp_make_shared_tag::_S_ti): Define
	function to get unique fake std::type_info reference.
	(_Sp_counted_ptr_inplace::_M_get_deleter) [!__cpp_rtti]: Compare to
	_S_ti() fake reference.
	(__shared_ptr(_Sp_make_shared_tag, const Alloc&, Args&&...)): Share
	single implementation with or without RTTI enable.
	[!__cpp_rtti]: Pass fake reference to _M_get_deleter.
	* testsuite/20_util/shared_ptr/creation/alloc.cc: Change expected
	allocation and deallocation counts.
	* testsuite/20_util/shared_ptr/creation/single_allocation.cc: New.
	* testsuite/20_util/shared_ptr/creation/single_allocation_no_rtti.cc:
	New.

Tested powerpc64le-linux, committed to trunk.

Attachment: patch.txt
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