cris: define HARD_FRAME_POINTER_REGNUM

cris: define HARD_FRAME_POINTER_REGNUM

Beware, tm.texi doesn't tell the whole story: a defined
HARD_FRAME_POINTER_REGNUM (different to FRAME_POINTER_REGNUM) is
supposed to make work easier for reload, being able to easily
tell actual frame-pointer-related addresses from those that
happen to use the same register or something to that effect.

On reasonable code the performance effect is barely measurable.

Looking at libgcc changes for -march=v10, the effect (where
noticeable) is mostly indeterminate churn.  Instances where it's
not just insns moved around at no obvious effect: one more insn
for addvdi3, subvdi3; two insns more in floatdisf; three insns
shorter fixunsdfdi.  Some of those seem related to pairing r8
with r9.  The only effect on coremark is an infinitesimal
positive effect from a three(!) cycles total (from the 15 calls)
faster execution paths in vfprintf_r.  Local microbenchmarks
give similar results.  With that in mind and not forgetting that
expectations in the register allocator and reload leaning
towards HARD_FRAME_POINTER_REGNUM defined (and different to)
FRAME_POINTER_REGNUM or to wit, "all the kids do it", why not.
Note that the offset at elimination really is 0.

gcc:
	* config/cris/cris.h (HARD_FRAME_POINTER_REGNUM): Define.
	Change FRAME_POINTER_REGNUM to correspond to a new faked
	register faked_fp, part of GENNONACR_REGS like faked_ap.
	(CRIS_FAKED_REGS_CONTENTS): New helper macro.
	(FIRST_PSEUDO_REGISTER, FIXED_REGISTERS, CALL_USED_REGISTERS):
	(REG_ALLOC_ORDER, REG_CLASS_CONTENTS, REGNO_OK_FOR_BASE_P)
	(ELIMINABLE_REGS, REGISTER_NAMES): Adjust accordingly.
	* config/cris/cris.md (CRIS_FP_REGNUM): Renumber to new faked
	register.
	(CRIS_REAL_FP_REGNUM): New constant.
	* config/cris/cris.c (cris_reg_saved_in_regsave_area): Check
	for HARD_FRAME_POINTER_REGNUM instead of FRAME_POINTER_REGNUM.
	(cris_initial_elimination_offset): Handle elimination changes
	to HARD_FRAME_POINTER_REGNUM instead of FRAME_POINTER_REGNUM
	and add one from FRAME_POINTER_REGNUM to
	HARD_FRAME_POINTER_REGNUM.
	(cris_expand_prologue, cris_expand_epilogue): Emit code for
	hard_frame_pointer_rtx instead of frame_pointer_rtx.