re PR debug/83941 (Debug info generated with -flto contains useless forwarders)

re PR debug/83941 (Debug info generated with -flto contains useless forwarders)

2018-09-25  Richard Biener  <rguenther@suse.de>

	PR debug/83941
	* dwarf2out.c (struct sym_off_pair): New.
	(external_die_map): New global.
	(lookup_decl_die): When in LTO create DIEs lazily from the
	external_die_map.
	(lookup_block_die): New function, create DIEs lazily in LTO.
	(equate_block_to_die): New function.
	(dwarf2out_die_ref_for_decl): During WPA get the association
	from the external DIE map.
	(dwarf2out_register_external_die): Record mapping into the
	external DIE map.
	(maybe_create_die_with_external_ref): New function split out from
	DIE generation part of old dwarf2out_register_external_die.
	(add_abstract_origin_attribute): Do not return the DIE.  When
	in LTO reference externals directly.
	(dwarf2out_abstract_function): When in LTO ignore calls for
	decls with external DIEs (already present abstract instances).
	(gen_call_site_die): Adjust.
	(add_high_low_attributes): Likewise.
	(gen_lexical_block_die): Likewise.
	(gen_inlined_subroutine_die): Likewie.
	(gen_block_die): Likewise.
	(dwarf2out_inline_entry): Likewise.
	(dwarf2out_early_finish): In LTRANS phase create DW_TAG_imported_unit
	DIEs.

From-SVN: r264564