xtensa: add --auto-litpools option

xtensa: add --auto-litpools option

Auto-litpools is the automated version of text-section-literals: literal
pool candidate frags are planted every N frags and during relaxation
they are turned into actual literal pools where literals are moved to
become reachable for their first reference by L32R instruction.

2015-08-12  David Weatherford  <weath@cadence.com>
gas/
	* config/tc-xtensa.c (struct litpool_frag, struct litpool_seg):
	New structures.
	(xtensa_maybe_create_literal_pool_frag): New function.
	(litpool_seg_list, auto_litpools, auto_litpool_limit)
	(litpool_buf, litpool_slotbuf): New static variables.
	(option_auto_litpools, option_no_auto_litpools)
	(option_auto_litpool_limit): New enum identifiers.
	(md_longopts): Add entries for auto-litpools, no-auto-litpools
	and auto-litpool-limit.
	(md_parse_option): Handle option_auto_litpools,
	option_no_auto_litpools and option_auto_litpool_limit.
	(md_show_usage): Add help for --[no-]auto-litpools and
	--auto-litpool-limit.
	(xtensa_mark_literal_pool_location): Record a place for literal
	pool with a call to xtensa_maybe_create_literal_pool_frag.
	(get_literal_pool_location): Find highest priority literal pool
	or convert candidate to literal pool when auto-litpools are used.
	(xg_assemble_vliw_tokens): Create literal pool after jump
	instruction.
	(xtensa_check_frag_count): Create candidate literal pool every
	auto_litpool_limit frags.
	(xtensa_relax_frag): Add jump around literals to non-empty
	literal pool.
	(xtensa_move_literals): Estimate literal pool addresses and move
	unreachable literals closer to their users, converting candidate
	to literal pool if needed.
	(xtensa_switch_to_non_abs_literal_fragment): Only emit error
	about missing .literal_position in case auto-litpools are not
	used.
	* config/tc-xtensa.h (xtensa_relax_statesE): New relaxation
	state: RELAX_LITERAL_POOL_CANDIDATE_BEGIN.
	* doc/as.texinfo (Xtensa options):  Document --auto-litpools and
	--no-auto-litpools options.
	* doc/c-xtensa.texi (Xtensa options): Likewise.

2015-08-12  Max Filippov  <jcmvbkbc@gmail.com>
gas/testsuite/
	* gas/xtensa/all.exp: Add auto-litpools to the list of xtensa
	tests.
	* gas/xtensa/auto-litpools.s: New file: auto-litpools test.
	* gas/xtensa/auto-litpools.s: New file: auto-litpools test
	result pattern.