%% -*- erlang-indent-level: 2 -*-
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%%     http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.

-module(hipe_spillcost).

-export([new/1,
	 inc_costs/2,
	 ref_in_bb/2,
	 spill_cost/2]).
%% The following is exported only for debugging purposes.
-ifdef(DEBUG_PRINTOUTS).
-export([nr_of_use/2]).
-endif.

%%----------------------------------------------------------------------------

-include("hipe_spillcost.hrl").

%%----------------------------------------------------------------------------

-spec new(non_neg_integer()) -> #spill_cost{}.

new(NrTemps) ->
  #spill_cost{uses = hipe_bifs:array(NrTemps, 0),
	      bb_uses = hipe_bifs:array(NrTemps, 0)}.

%%----------------------------------------------------------------------------
%% Function:    inc_costs
%%
%% Description: Registers usage of a list of temporaries (for spill_cost)
%%----------------------------------------------------------------------------

-spec inc_costs([non_neg_integer()], #spill_cost{}) -> #spill_cost{}.

inc_costs(Temps, SC) ->
  Uses = SC#spill_cost.uses,
  lists:foreach(fun (T) -> inc_use(T, Uses) end, Temps),
  SC. % updated via side-effects

inc_use(Temp, Uses) ->
  hipe_bifs:array_update(Uses, Temp, get_uses(Temp, Uses) + 1).

nr_of_use(Temp, SC) ->
  get_uses(Temp, SC#spill_cost.uses).

get_uses(Temp, Uses) ->
  hipe_bifs:array_sub(Uses, Temp).

%%----------------------------------------------------------------------------
%% Function:    ref_in_bb
%%
%% Description: Registers that a set of temporaries are used in one basic
%%              block; should be done exactly once per basic block
%%----------------------------------------------------------------------------

-spec ref_in_bb([non_neg_integer()], #spill_cost{}) -> #spill_cost{}.

ref_in_bb(Temps, SC) ->
  BBUses = SC#spill_cost.bb_uses,
  lists:foreach(fun (T) -> inc_bb_use(T, BBUses) end, Temps),
  SC. % updated via side-effects

inc_bb_use(Temp, BBUses) ->
  hipe_bifs:array_update(BBUses, Temp, get_bb_uses(Temp, BBUses) + 1).

bb_use(Temp, SC) ->
  get_bb_uses(Temp, SC#spill_cost.bb_uses).

get_bb_uses(Temp, BBUses) ->
  hipe_bifs:array_sub(BBUses, Temp).

%%----------------------------------------------------------------------------
%% Function:    spill_cost
%%
%% Description: Computes a spill cost for a temporary
%%   
%% Returns:
%%   Spill cost (a real number -- higher means worse to spill)
%%----------------------------------------------------------------------------

-spec spill_cost(non_neg_integer(), #spill_cost{}) -> float().

spill_cost(Temp, SC) ->
  nr_of_use(Temp, SC) / bb_use(Temp, SC).