Danila Fedorin
94278a6389
Introduce a finite-height lattice instance for Bool, then build the
reaching-definitions analysis on top of the forward framework:
* Spa/Lattice/Bool.lean: FiniteHeightLattice Bool (the two-element
lattice false ≤ true), making FiniteMap A Bool ks a finite-height
"power set" lattice for free.
* Spa/Analysis/Reaching.lean: DefSet prog = FiniteMap prog.State Bool
prog.states as the per-variable lattice of definition sites, with a
StmtEvaluator whose transfer function performs a strong update
(assignment to k at node s sets k's def-set to {s}).
The analysis computes a least fixed point and produces correct
reaching-definitions sets. Soundness (relating def-sets to actual
execution provenance) is deferred; not yet exposed in Spa.lean.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
43 lines
1.3 KiB
Lean4
43 lines
1.3 KiB
Lean4
import Spa.Lattice
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import Mathlib.Order.BooleanAlgebra
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namespace Spa
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/-! ### `Bool` as a finite-height lattice
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`Bool` is the two-element lattice `false ≤ true` (with `⊥ = false`, `⊤ = true`).
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It is the building block of the "power set" lattice `FiniteMap A Bool ks`, used by
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the reaching-definitions analysis to represent sets of definition sites. -/
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namespace Bool
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/-- Rank of a boolean: `false ↦ 0`, `true ↦ 1`. Used to bound chains, mirroring
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`AboveBelow.rank`. -/
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def rank : Bool → ℕ
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| false => 0
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| true => 1
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theorem rank_strictMono : StrictMono rank := by
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intro a b hab
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cases a <;> cases b <;> revert hab <;> decide
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theorem boundedChains : BoundedChains Bool 1 := fun c => by
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have h := LTSeries.head_add_length_le_nat (c.map rank rank_strictMono)
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rw [LTSeries.head_map, LTSeries.last_map, LTSeries.map_length] at h
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have h2 : rank c.last ≤ 1 := by cases c.last <;> simp [rank]
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omega
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instance : FiniteHeightLattice Bool where
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height := 1
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longestChain :=
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{ series := (RelSeries.singleton _ (⊥ : Bool)).snoc (⊤ : Bool)
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(by rw [RelSeries.last_singleton]; exact bot_lt_top)
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head_series := by simp
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last_series := by simp
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length_series := by simp [RelSeries.snoc, RelSeries.append] }
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chains_bounded := boundedChains
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end Bool
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end Spa
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