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From iris.heap_lang Require Export lang.
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From iris.prelude Require Import fin_maps.
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Import heap_lang.

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Module W.
Inductive expr :=
  | Val (v : val)
  | ClosedExpr (e : heap_lang.expr) `{!Closed [] e}
  (* Base lambda calculus *)
  | Var (x : string)
  | Rec (f x : binder) (e : expr)
  | App (e1 e2 : expr)
  (* Base types and their operations *)
  | Lit (l : base_lit)
  | UnOp (op : un_op) (e : expr)
  | BinOp (op : bin_op) (e1 e2 : expr)
  | If (e0 e1 e2 : expr)
  (* Products *)
  | Pair (e1 e2 : expr)
  | Fst (e : expr)
  | Snd (e : expr)
  (* Sums *)
  | InjL (e : expr)
  | InjR (e : expr)
  | Case (e0 : expr) (e1 : expr) (e2 : expr)
  (* Concurrency *)
  | Fork (e : expr)
  (* Heap *)
  | Alloc (e : expr)
  | Load (e : expr)
  | Store (e1 : expr) (e2 : expr)
  | CAS (e0 : expr) (e1 : expr) (e2 : expr).

Fixpoint to_expr (e : expr) : heap_lang.expr :=
  match e with
  | Val v => of_val v
  | ClosedExpr e _ => e
  | Var x => heap_lang.Var x
  | Rec f x e => heap_lang.Rec f x (to_expr e)
  | App e1 e2 => heap_lang.App (to_expr e1) (to_expr e2)
  | Lit l => heap_lang.Lit l
  | UnOp op e => heap_lang.UnOp op (to_expr e)
  | BinOp op e1 e2 => heap_lang.BinOp op (to_expr e1) (to_expr e2)
  | If e0 e1 e2 => heap_lang.If (to_expr e0) (to_expr e1) (to_expr e2)
  | Pair e1 e2 => heap_lang.Pair (to_expr e1) (to_expr e2)
  | Fst e => heap_lang.Fst (to_expr e)
  | Snd e => heap_lang.Snd (to_expr e)
  | InjL e => heap_lang.InjL (to_expr e)
  | InjR e => heap_lang.InjR (to_expr e)
  | Case e0 e1 e2 => heap_lang.Case (to_expr e0) (to_expr e1) (to_expr e2)
  | Fork e => heap_lang.Fork (to_expr e)
  | Alloc e => heap_lang.Alloc (to_expr e)
  | Load e => heap_lang.Load (to_expr e)
  | Store e1 e2 => heap_lang.Store (to_expr e1) (to_expr e2)
  | CAS e0 e1 e2 => heap_lang.CAS (to_expr e0) (to_expr e1) (to_expr e2)
  end.

Ltac of_expr e :=
  lazymatch e with
  | heap_lang.Var ?x => constr:(Var x)
  | heap_lang.Rec ?f ?x ?e => let e := of_expr e in constr:(Rec f x e)
  | heap_lang.App ?e1 ?e2 =>
     let e1 := of_expr e1 in let e2 := of_expr e2 in constr:(App e1 e2)
  | heap_lang.Lit ?l => constr:(Lit l)
  | heap_lang.UnOp ?op ?e => let e := of_expr e in constr:(UnOp op e)
  | heap_lang.BinOp ?op ?e1 ?e2 =>
     let e1 := of_expr e1 in let e2 := of_expr e2 in constr:(BinOp op e1 e2)
  | heap_lang.If ?e0 ?e1 ?e2 =>
     let e0 := of_expr e0 in let e1 := of_expr e1 in let e2 := of_expr e2 in
     constr:(If e0 e1 e2)
  | heap_lang.Pair ?e1 ?e2 =>
     let e1 := of_expr e1 in let e2 := of_expr e2 in constr:(Pair e1 e2)
  | heap_lang.Fst ?e => let e := of_expr e in constr:(Fst e)
  | heap_lang.Snd ?e => let e := of_expr e in constr:(Snd e)
  | heap_lang.InjL ?e => let e := of_expr e in constr:(InjL e)
  | heap_lang.InjR ?e => let e := of_expr e in constr:(InjR e)
  | heap_lang.Case ?e0 ?e1 ?e2 =>
     let e0 := of_expr e0 in let e1 := of_expr e1 in let e2 := of_expr e2 in
     constr:(Case e0 e1 e2)
  | heap_lang.Fork ?e => let e := of_expr e in constr:(Fork e)
  | heap_lang.Alloc ?e => let e := of_expr e in constr:(Alloc e)
  | heap_lang.Load ?e => let e := of_expr e in constr:(Load e)
  | heap_lang.Store ?e1 ?e2 =>
     let e1 := of_expr e1 in let e2 := of_expr e2 in constr:(Store e1 e2)
  | heap_lang.CAS ?e0 ?e1 ?e2 =>
     let e0 := of_expr e0 in let e1 := of_expr e1 in let e2 := of_expr e2 in
     constr:(CAS e0 e1 e2)
  | to_expr ?e => e
  | of_val ?v => constr:(Val v)
  | _ => constr:(ltac:(
     match goal with H : Closed [] e |- _ => exact (@ClosedExpr e H) end))
  end.

Fixpoint is_closed (X : list string) (e : expr) : bool :=
  match e with
  | Val _ | ClosedExpr _ _ => true
  | Var x => bool_decide (x  X)
  | Rec f x e => is_closed (f :b: x :b: X) e
  | Lit _ => true
  | UnOp _ e | Fst e | Snd e | InjL e | InjR e | Fork e | Alloc e | Load e =>
     is_closed X e
  | App e1 e2 | BinOp _ e1 e2 | Pair e1 e2 | Store e1 e2 =>
     is_closed X e1 && is_closed X e2
  | If e0 e1 e2 | Case e0 e1 e2 | CAS e0 e1 e2 =>
     is_closed X e0 && is_closed X e1 && is_closed X e2
  end.
Lemma is_closed_correct X e : is_closed X e  heap_lang.is_closed X (to_expr e).
Proof.
  revert X.
  induction e; naive_solver eauto using is_closed_of_val, is_closed_weaken_nil.
Qed.

Fixpoint to_val (e : expr) : option val :=
  match e with
  | Val v => Some v
  | Rec f x e =>
     if decide (is_closed (f :b: x :b: []) e) is left H
     then Some (@RecV f x (to_expr e) (is_closed_correct _ _ H)) else None
  | Lit l => Some (LitV l)
  | Pair e1 e2 => v1  to_val e1; v2  to_val e2; Some (PairV v1 v2)
  | InjL e => InjLV <$> to_val e
  | InjR e => InjRV <$> to_val e
  | _ => None
  end.
Lemma to_val_Some e v :
  to_val e = Some v  heap_lang.to_val (to_expr e) = Some v.
Proof.
  revert v. induction e; intros; simplify_option_eq; rewrite ?to_of_val; auto.
  - do 2 f_equal. apply proof_irrel.
  - exfalso. unfold Closed in *; eauto using is_closed_correct.
Qed.
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Lemma to_val_is_Some e :
  is_Some (to_val e)  is_Some (heap_lang.to_val (to_expr e)).
Proof. intros [v ?]; exists v; eauto using to_val_Some. Qed.
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Fixpoint subst (x : string) (es : expr) (e : expr)  : expr :=
  match e with
  | Val v => Val v
  | ClosedExpr e H => @ClosedExpr e H
  | Var y => if decide (x = y) then es else Var y
  | Rec f y e =>
     Rec f y $ if decide (BNamed x  f  BNamed x  y) then subst x es e else e
  | App e1 e2 => App (subst x es e1) (subst x es e2)
  | Lit l => Lit l
  | UnOp op e => UnOp op (subst x es e)
  | BinOp op e1 e2 => BinOp op (subst x es e1) (subst x es e2)
  | If e0 e1 e2 => If (subst x es e0) (subst x es e1) (subst x es e2)
  | Pair e1 e2 => Pair (subst x es e1) (subst x es e2)
  | Fst e => Fst (subst x es e)
  | Snd e => Snd (subst x es e)
  | InjL e => InjL (subst x es e)
  | InjR e => InjR (subst x es e)
  | Case e0 e1 e2 => Case (subst x es e0) (subst x es e1) (subst x es e2)
  | Fork e => Fork (subst x es e)
  | Alloc e => Alloc (subst x es e)
  | Load e => Load (subst x es e)
  | Store e1 e2 => Store (subst x es e1) (subst x es e2)
  | CAS e0 e1 e2 => CAS (subst x es e0) (subst x es e1) (subst x es e2)
  end.
Lemma to_expr_subst x er e :
  to_expr (subst x er e) = heap_lang.subst x (to_expr er) (to_expr e).
Proof.
  induction e; simpl; repeat case_decide;
    f_equal; auto using is_closed_nil_subst, is_closed_of_val, eq_sym.
Qed.
End W.

Ltac solve_closed :=
  match goal with
  | |- Closed ?X ?e =>
     let e' := W.of_expr e in change (Closed X (W.to_expr e'));
     apply W.is_closed_correct; vm_compute; exact I
  end.
Hint Extern 0 (Closed _ _) => solve_closed : typeclass_instances.

Ltac solve_to_val :=
  try match goal with
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  | |- context E [language.to_val ?e] =>
     let X := context E [to_val e] in change X
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  end;
  match goal with
  | |- to_val ?e = Some ?v =>
     let e' := W.of_expr e in change (to_val (W.to_expr e') = Some v);
     apply W.to_val_Some; simpl; reflexivity
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  | |- is_Some (to_val ?e) =>
     let e' := W.of_expr e in change (is_Some (to_val (W.to_expr e')));
     apply W.to_val_is_Some, (bool_decide_unpack _); vm_compute; exact I
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  end.

(** Substitution *)
Ltac simpl_subst :=
  csimpl;
  repeat match goal with
  | |- context [subst ?x ?er ?e] =>
      let er' := W.of_expr er in let e' := W.of_expr e in
      change (subst x er e) with (subst x (W.to_expr er') (W.to_expr e'));
      rewrite <-(W.to_expr_subst x); simpl (* ssr rewrite is slower *)
  end;
  unfold W.to_expr.
Arguments W.to_expr : simpl never.
Arguments subst : simpl never.

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(** The tactic [inv_head_step] performs inversion on hypotheses of the
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shape [head_step]. The tactic will discharge head-reductions starting
from values, and simplifies hypothesis related to conversions from and
to values, and finite map operations. This tactic is slightly ad-hoc
and tuned for proving our lifting lemmas. *)
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Ltac inv_head_step :=
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  repeat match goal with
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  | _ => progress simplify_map_eq/= (* simplify memory stuff *)
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  | H : to_val _ = Some _ |- _ => apply of_to_val in H
  | H : context [to_val (of_val _)] |- _ => rewrite to_of_val in H
  | H : head_step ?e _ _ _ _ |- _ =>
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     try (is_var e; fail 1); (* inversion yields many goals if [e] is a variable
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     and can thus better be avoided. *)
     inversion H; subst; clear H
  end.

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(** The tactic [reshape_expr e tac] decomposes the expression [e] into an
evaluation context [K] and a subexpression [e']. It calls the tactic [tac K e']
for each possible decomposition until [tac] succeeds. *)
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Ltac reshape_val e tac :=
  let rec go e :=
  match e with
  | of_val ?v => v
  | Rec ?f ?x ?e => constr:(RecV f x e)
  | Lit ?l => constr:(LitV l)
  | Pair ?e1 ?e2 =>
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    let v1 := go e1 in let v2 := go e2 in constr:(PairV v1 v2)
  | InjL ?e => let v := go e in constr:(InjLV v)
  | InjR ?e => let v := go e in constr:(InjRV v)
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  end in let v := go e in first [tac v | fail 2].

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Ltac reshape_expr e tac :=
  let rec go K e :=
  match e with
  | _ => tac (reverse K) e
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  | App ?e1 ?e2 => reshape_val e1 ltac:(fun v1 => go (AppRCtx v1 :: K) e2)
  | App ?e1 ?e2 => go (AppLCtx e2 :: K) e1
  | UnOp ?op ?e => go (UnOpCtx op :: K) e
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  | BinOp ?op ?e1 ?e2 =>
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     reshape_val e1 ltac:(fun v1 => go (BinOpRCtx op v1 :: K) e2)
  | BinOp ?op ?e1 ?e2 => go (BinOpLCtx op e2 :: K) e1
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  | If ?e0 ?e1 ?e2 => go (IfCtx e1 e2 :: K) e0
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  | Pair ?e1 ?e2 => reshape_val e1 ltac:(fun v1 => go (PairRCtx v1 :: K) e2)
  | Pair ?e1 ?e2 => go (PairLCtx e2 :: K) e1
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  | Fst ?e => go (FstCtx :: K) e
  | Snd ?e => go (SndCtx :: K) e
  | InjL ?e => go (InjLCtx :: K) e
  | InjR ?e => go (InjRCtx :: K) e
  | Case ?e0 ?e1 ?e2 => go (CaseCtx e1 e2 :: K) e0
  | Alloc ?e => go (AllocCtx :: K) e
  | Load ?e => go (LoadCtx :: K) e
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  | Store ?e1 ?e2 => reshape_val e1 ltac:(fun v1 => go (StoreRCtx v1 :: K) e2)
  | Store ?e1 ?e2 => go (StoreLCtx e2 :: K) e1
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  | CAS ?e0 ?e1 ?e2 => reshape_val e0 ltac:(fun v0 => first
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     [ reshape_val e1 ltac:(fun v1 => go (CasRCtx v0 v1 :: K) e2)
     | go (CasMCtx v0 e2 :: K) e1 ])
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  | CAS ?e0 ?e1 ?e2 => go (CasLCtx e1 e2 :: K) e0
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  end in go (@nil ectx_item) e.

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(** The tactic [do_head_step tac] solves goals of the shape [head_reducible] and
[head_step] by performing a reduction step and uses [tac] to solve any
side-conditions generated by individual steps. *)
Tactic Notation "do_head_step" tactic3(tac) :=
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  try match goal with |- head_reducible _ _ => eexists _, _, _ end;
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  simpl;
  match goal with
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  | |- head_step ?e1 ?σ1 ?e2 ?σ2 ?ef =>
     first [apply alloc_fresh|econstructor];
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       (* solve [to_val] side-conditions *)
       first [rewrite ?to_of_val; reflexivity|simpl_subst; tac; fast_done]
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  end.