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%%% -*- erlang-indent-level: 2 -*-
%%% $Id$
-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.
-type(hipe_array() :: integer()).
-record(spill_cost,
{uses :: hipe_array(), % number of uses of each temp
bb_uses :: hipe_array() % number of basic blocks each temp occurs in
}).
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)
%%----------------------------------------------------------------------
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
%%----------------------------------------------------------------------
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)
%%----------------------------------------------------------------------
spill_cost(Temp, SC) ->
nr_of_use(Temp, SC) / bb_use(Temp, SC).
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