57 lines
1.7 KiB
Text
57 lines
1.7 KiB
Text
/-
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Copyright (c) 2019 Microsoft Corporation. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Authors: Leonardo de Moura
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-/
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prelude
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import init.lean.compiler.ir.basic
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namespace Lean
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namespace IR
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private def maxOccs (alts : Array Alt) : Alt × Nat :=
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alts.iterateFrom (alts.get 0, 1) 1 $ λ i a p,
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let aBody := a.body in
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let noccs := alts.iterateFrom 1 (i.val + 1) $ λ _ a' n,
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if a'.body == aBody then n+1 else n in
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if noccs > p.2 then (a, noccs) else p
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private def addDefault (alts : Array Alt) : Array Alt :=
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if alts.size <= 1 || alts.any Alt.isDefault then alts
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else
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let (max, noccs) := maxOccs alts in
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if noccs == 1 then alts
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else
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let alts := alts.filter $ (λ alt, alt.body != max.body) in
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alts.push (Alt.default max.body)
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private def mkSimpCase (tid : Name) (x : VarId) (alts : Array Alt) : FnBody :=
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let alts := alts.filter (λ alt, alt.body != FnBody.unreachable) in
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let alts := addDefault alts in
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if alts.size == 0 then
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FnBody.unreachable
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else if alts.size == 1 then
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(alts.get 0).body
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else
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FnBody.case tid x alts
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partial def FnBody.simpCase : FnBody → FnBody
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| b :=
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let (bs, term) := b.flatten in
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let bs := modifyJPs bs FnBody.simpCase in
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match term with
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| FnBody.case tid x alts :=
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let alts := alts.hmap $ λ alt, alt.modifyBody FnBody.simpCase in
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reshape bs (mkSimpCase tid x alts)
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| other := reshape bs term
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/-- Simplify `case`
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- Remove unreachable branches.
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- Remove `case` if there is only one branch.
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- Merge most common branches using `Alt.default`. -/
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def Decl.simpCase : Decl → Decl
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| (Decl.fdecl f xs t b) := Decl.fdecl f xs t b.simpCase
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| other := other
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end IR
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end Lean
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