44 lines
1.3 KiB
OCaml
44 lines
1.3 KiB
OCaml
(** Dead Code Elimination *)
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open Ll
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open Datastructures
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(* expose a top-level analysis operation ------------------------------------ *)
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(* TASK: This function should optimize a block by removing dead instructions
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- lb: a function from uids to the live-OUT set at the
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corresponding program point
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- ab: the alias map flowing IN to each program point in the block
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- b: the current ll block
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Note:
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Call instructions are never considered to be dead (they might produce
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side effects)
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Store instructions are not dead if the pointer written to is live _or_
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the pointer written to may be aliased.
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Other instructions are dead if the value they compute is not live.
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Hint: Consider using List.filter
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*)
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let dce_block (lb:uid -> Liveness.Fact.t)
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(ab:uid -> Alias.fact)
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(b:Ll.block) : Ll.block =
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failwith "Dce.dce_block unimplemented"
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let run (lg:Liveness.Graph.t) (ag:Alias.Graph.t) (cfg:Cfg.t) : Cfg.t =
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LblS.fold (fun l cfg ->
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let b = Cfg.block cfg l in
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(* compute liveness at each program point for the block *)
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let lb = Liveness.Graph.uid_out lg l in
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(* compute aliases at each program point for the block *)
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let ab = Alias.Graph.uid_in ag l in
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(* compute optimized block *)
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let b' = dce_block lb ab b in
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Cfg.add_block l b' cfg
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) (Cfg.nodes cfg) cfg
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