(* * Copyright (c) 1997-1999 Massachusetts Institute of Technology * Copyright (c) 2003, 2007-8 Matteo Frigo * Copyright (c) 2003, 2007-8 Massachusetts Institute of Technology * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA * *) (* This file contains the instruction scheduler, which finds an efficient ordering for a given list of instructions. The scheduler analyzes the DAG (directed acyclic graph) formed by the instruction dependencies, and recursively partitions it. The resulting schedule data structure expresses a "good" ordering and structure for the computation. The scheduler makes use of utilties in Dag and other packages to manipulate the Dag and the instruction list. *) open Dag (************************************************* * Dag scheduler *************************************************) let to_assignment node = (Expr.Assign (node.assigned, node.expression)) let makedag l = Dag.makedag (List.map (function Expr.Assign (v, x) -> (v, x)) l) let return x = x let has_color c n = (n.color = c) let set_color c n = (n.color <- c) let has_either_color c1 c2 n = (n.color = c1 || n.color = c2) let infinity = 100000 let cc dag inputs = begin Dag.for_all dag (fun node -> node.label <- infinity); (match inputs with a :: _ -> bfs dag a 0 | _ -> failwith "connected"); return ((List.map to_assignment (List.filter (fun n -> n.label < infinity) (Dag.to_list dag))), (List.map to_assignment (List.filter (fun n -> n.label == infinity) (Dag.to_list dag)))) end let rec connected_components alist = let dag = makedag alist in let inputs = List.filter (fun node -> Util.null node.predecessors) (Dag.to_list dag) in match cc dag inputs with (a, []) -> [a] | (a, b) -> a :: connected_components b let single_load node = match (node.input_variables, node.predecessors) with ([x], []) -> Variable.is_constant x || (!Magic.locations_are_special && Variable.is_locative x) | _ -> false let loads_locative node = match (node.input_variables, node.predecessors) with | ([x], []) -> Variable.is_locative x | _ -> false let partition alist = let dag = makedag alist in let dag' = Dag.to_list dag in let inputs = List.filter (fun node -> Util.null node.predecessors) dag' and outputs = List.filter (fun node -> Util.null node.successors) dag' and special_inputs = List.filter single_load dag' in begin let c = match !Magic.schedule_type with | 1 -> RED; (* all nodes in the input partition *) | -1 -> BLUE; (* all nodes in the output partition *) | _ -> BLACK; (* node color determined by bisection algorithm *) in Dag.for_all dag (fun node -> node.color <- c); Util.for_list inputs (set_color RED); (* The special inputs are those input nodes that load a single location or twiddle factor. Special inputs can end up either in the blue or in the red part. These inputs are special because they inherit a color from their neighbors: If a red node needs a special input, the special input becomes red, but if all successors of a special input are blue, the special input becomes blue. Outputs are always blue, whether they be special or not. Because of the processing of special inputs, however, the final partition might end up being composed only of blue nodes (which is incorrect). In this case we manually reset all inputs (whether special or not) to be red. *) Util.for_list special_inputs (set_color YELLOW); Util.for_list outputs (set_color BLUE); let rec loopi donep = match (List.filter (fun node -> (has_color BLACK node) && List.for_all (has_either_color RED YELLOW) node.predecessors) dag') with [] -> if (donep) then () else loopo true | i -> begin Util.for_list i (fun node -> begin set_color RED node; Util.for_list node.predecessors (set_color RED); end); loopo false; end and loopo donep = match (List.filter (fun node -> (has_either_color BLACK YELLOW node) && List.for_all (has_color BLUE) node.successors) dag') with [] -> if (donep) then () else loopi true | o -> begin Util.for_list o (set_color BLUE); loopi false; end in loopi false; (* fix the partition if it is incorrect *) if not (List.exists (has_color RED) dag') then Util.for_list inputs (set_color RED); return ((List.map to_assignment (List.filter (has_color RED) dag')), (List.map to_assignment (List.filter (has_color BLUE) dag'))) end type schedule = Done | Instr of Expr.assignment | Seq of (schedule * schedule) | Par of schedule list (* produce a sequential schedule determined by the user *) let rec sequentially = function [] -> Done | a :: b -> Seq (Instr a, sequentially b) let schedule = let rec schedule_alist = function | [] -> Done | [a] -> Instr a | alist -> match connected_components alist with | ([a]) -> schedule_connected a | l -> Par (List.map schedule_alist l) and schedule_connected alist = match partition alist with | (a, b) -> Seq (schedule_alist a, schedule_alist b) in fun x -> let () = Util.info "begin schedule" in let res = schedule_alist x in let () = Util.info "end schedule" in res (* partition a dag into two parts: 1) the set of loads from locatives and their successors, 2) all other nodes This step separates the ``body'' of the dag, which computes the actual fft, from the ``precomputations'' part, which computes e.g. twiddle factors. *) let partition_precomputations alist = let dag = makedag alist in let dag' = Dag.to_list dag in let loads = List.filter loads_locative dag' in begin Dag.for_all dag (set_color BLUE); Util.for_list loads (set_color RED); let rec loop () = match (List.filter (fun node -> (has_color RED node) && List.exists (has_color BLUE) node.successors) dag') with [] -> () | i -> begin Util.for_list i (fun node -> Util.for_list node.successors (set_color RED)); loop () end in loop (); return ((List.map to_assignment (List.filter (has_color BLUE) dag')), (List.map to_assignment (List.filter (has_color RED) dag'))) end let isolate_precomputations_and_schedule alist = let (a, b) = partition_precomputations alist in Seq (schedule a, schedule b)