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From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/103252] questionable codegen with kmovd
Date: Wed, 24 Nov 2021 05:47:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103252

--- Comment #14 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Hongtao.liu from comment #13)
> >=20
> > So for short live range reg, we may lose opportunity to allocate best
> > regclass, maybe add peephole2 to handle those cases instead of tune RA.
> No, r132 is also used as addr, but currently lra only add cost of movement
> from  mask to gpr, but we could possibly run out of gpr which means there
> will be an extra spill, and this is not counted by record_address_regs.
>=20
> modified   gcc/ira-costs.c
> @@ -1226,7 +1226,7 @@ record_address_regs (machine_mode mode, addr_space_t
> as, rtx x,
>  	struct costs *pp;
>  	int *pp_costs;
>  	enum reg_class i;
> -	int k, regno, add_cost;
> +	int k, regno, add_cost, potential_spill_cost;
>  	cost_classes_t cost_classes_ptr;
>  	enum reg_class *cost_classes;
>  	move_table *move_in_cost;
> @@ -1239,6 +1239,7 @@ record_address_regs (machine_mode mode, addr_space_t
> as, rtx x,
>  	  ALLOCNO_BAD_SPILL_P (ira_curr_regno_allocno_map[regno]) =3D true;
>  	pp =3D COSTS (costs, COST_INDEX (regno));
>  	add_cost =3D (ira_memory_move_cost[Pmode][rclass][1] * scale) / 2;
> +	potential_spill_cost =3D add_cost / 5;
>  	if (INT_MAX - add_cost < pp->mem_cost)
>  	  pp->mem_cost =3D INT_MAX;
>  	else
> @@ -1252,6 +1253,10 @@ record_address_regs (machine_mode mode, addr_space=
_t
> as, rtx x,
>  	  {
>  	    i =3D cost_classes[k];
>  	    add_cost =3D (move_in_cost[i][rclass] * scale) / 2;
> +	    /* If we run out of rclass regs, there could be an extra spill,
> +	       Let's say 20% possibility.  */
> +	    if (!ira_class_subset_p[i][rclass])
> +	      add_cost +=3D potential_spill_cost;
>  	    if (INT_MAX - add_cost < pp_costs[k])
>  	      pp_costs[k] =3D INT_MAX;

Increase cost will lose some spill to mask opportunity like testcase
https://gcc.godbolt.org/z/KG63ErzEr=