xtensa: add -mauto-litpools option

xtensa: add -mauto-litpools option

With support from assembler this option allows compiling huge functions,
where single literal pool at the beginning of a function may not be
reachable by L32R instructions at its end.

Currently assembler --auto-litpools option cannot deal with literals
used from multiple locations separated by more than 256 KBytes of code.
Don't turn constants into literals, instead use MOVI instruction to load
them into registers and let the assembler turn them into literals as
necessary.

2015-08-12  Max Filippov  <jcmvbkbc@gmail.com>
gcc/
	* config/xtensa/constraints.md (define_constraint "Y"): New
	constraint.
	* config/xtensa/elf.h (ASM_SPEC): Add m(no-)auto-litpools.
	* config/xtensa/linux.h (ASM_SPEC): Likewise.
	* config/xtensa/predicates.md (move_operand): Match constants
	and symbols in the presence of TARGET_AUTO_LITPOOLS.
	* config/xtensa/xtensa.c (xtensa_valid_move): Don't allow
	immediate references to TLS data.
	(xtensa_emit_move_sequence): Don't force constants to memory in
	the presence of TARGET_AUTO_LITPOOLS.
	(print_operand): Add 'y' format, same as default, but capable of
	printing SF mode constants as well.
	* config/xtensa/xtensa.md (movsi_internal, movhi_internal)
	(movsf_internal): Add movi pattern that loads literal.
	(movsf, movdf): Don't force constants to memory in the presence
	of TARGET_AUTO_LITPOOLS.
	(movdf_internal): Add 'Y' constraint.
	* config/xtensa/xtensa.opt (mauto-litpools): New option.
	* doc/invoke.text (Xtensa options): Document -mauto-litpools.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@226828 138bc75d-0d04-0410-961f-82ee72b054a4