Re: [2/9] Add a REG_NREGS macro

[Richard Sandiford <richard.sandiford@arm.com>]

Jeff Law <law@redhat.com> writes:
> On 05/18/2015 12:13 PM, Richard Sandiford wrote:
>> This patch adds a REG_NREGS macro that by the end of the series
>> will simply be an rtx field access.  The definition in this patch
>> is just a placeholder (and so I haven't tried to avoid the double
>> evaluation of the parameter).
>>
>> The diff has extra context because in most cases it makes it obvious
>> that we really are looking at hard_regno_nregs[REGNO (x)][GET_MODE (x)]
>> for some rtx x.  There are a couple of sites where it's more indirect
>> though.
>>
>>
>> gcc/
>> 	* rtl.h (REG_NREGS): New macro
>> 	* alias.c (record_set): Use it.
>> 	* cfgcleanup.c (mark_effect): Likewise.
>> 	* combine.c (likely_spilled_retval_1): Likewise.
>> 	(likely_spilled_retval_p, can_change_dest_mode): Likewise.
>> 	(move_deaths, distribute_notes): Likewise.
>> 	* cselib.c (cselib_record_set): Likewise.
>> 	* df-problems.c (df_simulate_one_insn_forwards): Likewise.
>> 	* df-scan.c (df_mark_reg): Likewise.
>> 	* dse.c (look_for_hardregs): Likewise.
>> 	* dwarf2out.c (reg_loc_descriptor): Likewise.
>> 	(multiple_reg_loc_descriptor): Likewise.
>> 	* expr.c (write_complex_part, read_complex_part): Likewise.
>> 	(emit_move_complex): Likewise.
>> 	* haifa-sched.c (setup_ref_regs): Likewise.
>> 	* ira-lives.c (mark_hard_reg_live): Likewise.
>> 	* lra.c (lra_set_insn_recog_data): Likewise.
>> 	* mode-switching.c (create_pre_exit): Likewise.
>> 	* postreload.c (reload_combine_recognize_const_pattern): Likewise.
>> 	(reload_combine_recognize_pattern): Likewise.
>> 	(reload_combine_note_use, move2add_record_mode): Likewise.
>> 	(reload_cse_move2add): Likewise.
>> 	* reg-stack.c (subst_stack_regs_pat): Likewise.
>> 	* regcprop.c (kill_value, copy_value): Likewise.
>> 	(copyprop_hardreg_forward_1): Likewise.
>> 	* regrename.c (verify_reg_in_set, scan_rtx_reg): Likewise.
>> 	(build_def_use): Likewise.
>> 	* sched-deps.c (mark_insn_reg_birth, mark_reg_death): Likewise.
>> 	(deps_analyze_insn): Likewise.
>> 	* sched-rgn.c (check_live_1, update_live_1): Likewise.
>> 	* sel-sched.c (count_occurrences_equiv): Likewise.
>> 	* valtrack.c (dead_debug_insert_temp): Likewise.
>>
> OK.
>
> Makes me wonder if we want to poison hard_regno_nregs in some way to 
> avoid folks re-introducing this stuff in the future...  Your call if you 
> want to tackle that as a follow-up.

The problem is that many uses of hard_regno_nregs aren't about
existing REGs.  E.g. the register allocators need to know how many
registers something would occupy before allocating it, so they (rightly)
make heavy use of it with a calculated regno and/or mode.

Agree that people will probably do things the old way out of habit.
Maybe it's just something I should grep for occasionally...

Thanks,
Richard