[NDS32] Implement fp-as-gp optimization.

[NDS32] Implement fp-as-gp optimization.

gcc/
	* config/nds32/constants.md (unspec_volatile_element): Add
	UNSPEC_VOLATILE_OMIT_FP_BEGIN and UNSPEC_VOLATILE_OMIT_FP_END.
	* config/nds32/nds32-fp-as-gp.c: New implementation of fp_as_gp
	optimization.
	* config/nds32/nds32-protos.h (nds32_naked_function_p): Declare.
	(make_pass_nds32_fp_as_gp): Declare.
	* config/nds32/nds32.c (nds32_register_passes): Add fp_as_gp as one
	optmization pass.
	(nds32_asm_function_end_prologue): Remove unused asm output.
	(nds32_asm_function_begin_epilogue): Remove unused asm output.
	(nds32_asm_file_start): Output necessary fp_as_gp information.
	(nds32_option_override): Adjust register usage.
	(nds32_expand_prologue): Consider fp_as_gp situation.
	(nds32_expand_prologue_v3push): Consider fp_as_gp situation.
	* config/nds32/nds32.md (prologue): Check fp_as_gp_p and naked_p.
	(epilogue): Ditto.
	(return): Ditto.
	(simple_return): Ditto.
	(omit_fp_begin): Output special directive for fp_as_gp.
	(omit_fp_end): Output special directive for fp_as_gp.
	* config/nds32/nds32.opt (mfp-as-gp, mno-fp-as-gp, mforce-fp-as-gp,
	mforbid-fp-as-gp): New options.

Co-Authored-By: Shiva Chen <shiva0217@gmail.com>
From-SVN: r261115