237 lines
7.1 KiB
OCaml
237 lines
7.1 KiB
OCaml
(*
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* Copyright (c) 1997-1999 Massachusetts Institute of Technology
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* Copyright (c) 2003, 2007-14 Matteo Frigo
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* Copyright (c) 2003, 2007-14 Massachusetts Institute of Technology
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*
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*)
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(* This file contains the instruction scheduler, which finds an
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efficient ordering for a given list of instructions.
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The scheduler analyzes the DAG (directed acyclic graph) formed by
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the instruction dependencies, and recursively partitions it. The
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resulting schedule data structure expresses a "good" ordering
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and structure for the computation.
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The scheduler makes use of utilties in Dag and other packages to
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manipulate the Dag and the instruction list. *)
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open Dag
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(*************************************************
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* Dag scheduler
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*************************************************)
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let to_assignment node = (Expr.Assign (node.assigned, node.expression))
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let makedag l = Dag.makedag
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(List.map (function Expr.Assign (v, x) -> (v, x)) l)
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let return x = x
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let has_color c n = (n.color = c)
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let set_color c n = (n.color <- c)
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let has_either_color c1 c2 n = (n.color = c1 || n.color = c2)
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let infinity = 100000
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let cc dag inputs =
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begin
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Dag.for_all dag (fun node ->
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node.label <- infinity);
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(match inputs with
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a :: _ -> bfs dag a 0
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| _ -> failwith "connected");
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return
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((List.map to_assignment (List.filter (fun n -> n.label < infinity)
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(Dag.to_list dag))),
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(List.map to_assignment (List.filter (fun n -> n.label == infinity)
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(Dag.to_list dag))))
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end
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let rec connected_components alist =
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let dag = makedag alist in
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let inputs =
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List.filter (fun node -> Util.null node.predecessors)
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(Dag.to_list dag) in
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match cc dag inputs with
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(a, []) -> [a]
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| (a, b) -> a :: connected_components b
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let single_load node =
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match (node.input_variables, node.predecessors) with
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([x], []) ->
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Variable.is_constant x ||
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(!Magic.locations_are_special && Variable.is_locative x)
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| _ -> false
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let loads_locative node =
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match (node.input_variables, node.predecessors) with
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| ([x], []) -> Variable.is_locative x
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| _ -> false
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let partition alist =
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let dag = makedag alist in
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let dag' = Dag.to_list dag in
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let inputs =
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List.filter (fun node -> Util.null node.predecessors) dag'
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and outputs =
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List.filter (fun node -> Util.null node.successors) dag'
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and special_inputs = List.filter single_load dag' in
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begin
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let c = match !Magic.schedule_type with
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| 1 -> RED; (* all nodes in the input partition *)
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| -1 -> BLUE; (* all nodes in the output partition *)
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| _ -> BLACK; (* node color determined by bisection algorithm *)
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in Dag.for_all dag (fun node -> node.color <- c);
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Util.for_list inputs (set_color RED);
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(*
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The special inputs are those input nodes that load a single
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location or twiddle factor. Special inputs can end up either
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in the blue or in the red part. These inputs are special
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because they inherit a color from their neighbors: If a red
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node needs a special input, the special input becomes red, but
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if all successors of a special input are blue, the special
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input becomes blue. Outputs are always blue, whether they be
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special or not.
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Because of the processing of special inputs, however, the final
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partition might end up being composed only of blue nodes (which
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is incorrect). In this case we manually reset all inputs
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(whether special or not) to be red.
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*)
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Util.for_list special_inputs (set_color YELLOW);
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Util.for_list outputs (set_color BLUE);
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let rec loopi donep =
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match (List.filter
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(fun node -> (has_color BLACK node) &&
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List.for_all (has_either_color RED YELLOW) node.predecessors)
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dag') with
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[] -> if (donep) then () else loopo true
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| i ->
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begin
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Util.for_list i (fun node ->
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begin
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set_color RED node;
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Util.for_list node.predecessors (set_color RED);
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end);
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loopo false;
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end
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and loopo donep =
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match (List.filter
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(fun node -> (has_either_color BLACK YELLOW node) &&
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List.for_all (has_color BLUE) node.successors)
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dag') with
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[] -> if (donep) then () else loopi true
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| o ->
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begin
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Util.for_list o (set_color BLUE);
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loopi false;
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end
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in loopi false;
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(* fix the partition if it is incorrect *)
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if not (List.exists (has_color RED) dag') then
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Util.for_list inputs (set_color RED);
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return
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((List.map to_assignment (List.filter (has_color RED) dag')),
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(List.map to_assignment (List.filter (has_color BLUE) dag')))
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end
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type schedule =
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Done
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| Instr of Expr.assignment
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| Seq of (schedule * schedule)
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| Par of schedule list
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(* produce a sequential schedule determined by the user *)
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let rec sequentially = function
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[] -> Done
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| a :: b -> Seq (Instr a, sequentially b)
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let schedule =
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let rec schedule_alist = function
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| [] -> Done
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| [a] -> Instr a
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| alist -> match connected_components alist with
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| ([a]) -> schedule_connected a
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| l -> Par (List.map schedule_alist l)
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and schedule_connected alist =
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match partition alist with
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| (a, b) -> Seq (schedule_alist a, schedule_alist b)
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in fun x ->
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let () = Util.info "begin schedule" in
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let res = schedule_alist x in
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let () = Util.info "end schedule" in
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res
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(* partition a dag into two parts:
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1) the set of loads from locatives and their successors,
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2) all other nodes
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This step separates the ``body'' of the dag, which computes the
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actual fft, from the ``precomputations'' part, which computes e.g.
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twiddle factors.
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*)
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let partition_precomputations alist =
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let dag = makedag alist in
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let dag' = Dag.to_list dag in
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let loads = List.filter loads_locative dag' in
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begin
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Dag.for_all dag (set_color BLUE);
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Util.for_list loads (set_color RED);
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let rec loop () =
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match (List.filter
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(fun node -> (has_color RED node) &&
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List.exists (has_color BLUE) node.successors)
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dag') with
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[] -> ()
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| i ->
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begin
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Util.for_list i
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(fun node ->
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Util.for_list node.successors (set_color RED));
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loop ()
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end
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in loop ();
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return
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((List.map to_assignment (List.filter (has_color BLUE) dag')),
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(List.map to_assignment (List.filter (has_color RED) dag')))
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end
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let isolate_precomputations_and_schedule alist =
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let (a, b) = partition_precomputations alist in
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Seq (schedule a, schedule b)
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