(* *********************************************************************)
(*                                                                     *)
(*              The Compcert verified compiler                         *)
(*                                                                     *)
(*          Xavier Leroy, INRIA Paris-Rocquencourt                     *)
(*                                                                     *)
(*  Copyright Institut National de Recherche en Informatique et en     *)
(*  Automatique.  All rights reserved.  This file is distributed       *)
(*  under the terms of the GNU General Public License as published by  *)
(*  the Free Software Foundation, either version 2 of the License, or  *)
(*  (at your option) any later version.  This file is also distributed *)
(*  under the terms of the INRIA Non-Commercial License Agreement.     *)
(*                                                                     *)
(* *********************************************************************)

(** The Clight language: a simplified version of Compcert C where all
  expressions are pure and assignments and function calls are
  statements, not expressions. *)

Require Import Coqlib.
Require Import Errors.
Require Import Maps.
Require Import Integers.
Require Import Floats.
Require Import Values.
Require Import AST.
Require Import Memory.
Require Import Events.
Require Import Globalenvs.
Require Import Smallstep.
Require Import Csyntax.
Require Import Csem.

(** * Abstract syntax *)


(** ** Expressions *)

(** Clight expressions correspond to the "pure" subset of C expressions.
  The main omissions are string literals and assignment operators
  ([=], [+=], [++], etc).  In Clight, assignment is a statement,
  not an expression.  Additionally, an expression can also refer to
  temporary variables, which are a separate class of local variables
  that do not reside in memory and whose address cannot be taken.

  As in Compcert C, all expressions are annotated with their types,
  as needed to resolve operator overloading and type-dependent behaviors. *)

Inductive expr : Type :=
  | Econst_int: int -> type -> expr       (**r integer literal *)
  | Econst_float: float -> type -> expr   (**r float literal *)
  | Evar: ident -> type -> expr           (**r variable *)
  | Etempvar: ident -> type -> expr       (**r temporary variable *)
  | Ederef: expr -> type -> expr          (**r pointer dereference (unary [*]) *)
  | Eaddrof: expr -> type -> expr         (**r address-of operator ([&]) *)
  | Eunop: unary_operation -> expr -> type -> expr  (**r unary operation *)
  | Ebinop: binary_operation -> expr -> expr -> type -> expr (**r binary operation *)
  | Ecast: expr -> type -> expr   (**r type cast ([(ty) e]) *)
  | Efield: expr -> ident -> type -> expr. (**r access to a member of a struct or union *)

(** [sizeof] and [alignof] are derived forms. *)

Definition Esizeof (ty' ty: type) : expr := Econst_int (Int.repr(sizeof ty')) ty.
Definition Ealignof (ty' ty: type) : expr := Econst_int (Int.repr(alignof ty')) ty.

(** Extract the type part of a type-annotated Clight expression. *)

Definition typeof (e: expr) : type :=
  match e with
  | Econst_int _ ty => ty
  | Econst_float _ ty => ty
  | Evar _ ty => ty
  | Etempvar _ ty => ty
  | Ederef _ ty => ty
  | Eaddrof _ ty => ty
  | Eunop _ _ ty => ty
  | Ebinop _ _ _ ty => ty
  | Ecast _ ty => ty
  | Efield _ _ ty => ty
  end.

(** ** Statements *)

(** Clight statements are similar to those of Compcert C, with the addition
  of assigment (of a rvalue to a lvalue), assignment to a temporary,
  and function call (with assignment of the result to a temporary).
  The three C loops are replaced by a single infinite loop [Sloop s1 s2]
  that executes [s1] then [s2] repeatedly.  A [continue] in [s1] branches to [s2]. *)

Definition label := ident.

Inductive statement : Type :=
  | Sskip : statement                   (**r do nothing *)
  | Sassign : expr -> expr -> statement (**r assignment [lvalue = rvalue] *)
  | Sset : ident -> expr -> statement   (**r assignment [tempvar = rvalue] *)
  | Scall: option ident -> expr -> list expr -> statement (**r function call *)
  | Sbuiltin: option ident -> external_function -> typelist -> list expr -> statement (**r builtin invocation *)
  | Ssequence : statement -> statement -> statement  (**r sequence *)
  | Sifthenelse : expr  -> statement -> statement -> statement (**r conditional *)
  | Sloop: statement -> statement -> statement (**r infinite loop *)
  | Sbreak : statement                      (**r [break] statement *)
  | Scontinue : statement                   (**r [continue] statement *)
  | Sreturn : option expr -> statement      (**r [return] statement *)
  | Sswitch : expr -> labeled_statements -> statement  (**r [switch] statement *)
  | Slabel : label -> statement -> statement
  | Sgoto : label -> statement

with labeled_statements : Type :=            (**r cases of a [switch] *)
  | LSdefault: statement -> labeled_statements
  | LScase: int -> statement -> labeled_statements -> labeled_statements.

(** The C loops are derived forms. *)

Definition Swhile (e: expr) (s: statement) :=
  Sloop (Ssequence (Sifthenelse e Sskip Sbreak) s) Sskip.

Definition Sdowhile (s: statement) (e: expr) :=
  Sloop s (Sifthenelse e Sskip Sbreak).

Definition Sfor (s1: statement) (e2: expr) (s3: statement) (s4: statement) :=
  Ssequence s1 (Sloop (Ssequence (Sifthenelse e2 Sskip Sbreak) s3) s4).

(** ** Functions *)

(** A function definition is composed of its return type ([fn_return]),
  the names and types of its parameters ([fn_params]), the names
  and types of its local variables ([fn_vars]), and the body of the
  function (a statement, [fn_body]). *)

Record function : Type := mkfunction {
  fn_return: type;
  fn_params: list (ident * type);
  fn_vars: list (ident * type);
  fn_temps: list (ident * type);
  fn_body: statement
}.

Definition var_names (vars: list(ident * type)) : list ident :=
  List.map (@fst ident type) vars.

(** Functions can either be defined ([Internal]) or declared as
  external functions ([External]). *)

Inductive fundef : Type :=
  | Internal: function -> fundef
  | External: external_function -> typelist -> type -> fundef.

(** ** Programs *)

(** A program is a collection of named functions, plus a collection
  of named global variables, carrying their types and optional initialization 
  data.  See module [AST] for more details. *)

Definition program : Type := AST.program fundef type.

(** * Operations over types *)

(** The type of a function definition. *)

Definition type_of_function (f: function) : type :=
  Tfunction (type_of_params (fn_params f)) (fn_return f).

Definition type_of_fundef (f: fundef) : type :=
  match f with
  | Internal fd => type_of_function fd
  | External id args res => Tfunction args res
  end.

(** * Operational semantics *)

(** The semantics uses two environments.  The global environment
  maps names of functions and global variables to memory block references,
  and function pointers to their definitions.  (See module [Globalenvs].) *)

Definition genv := Genv.t fundef type.

(** The local environment maps local variables to block references
  and types.  The current value of the variable is stored in the associated memory
  block. *)

Definition env := PTree.t (block * type). (* map variable -> location & type *)

Definition empty_env: env := (PTree.empty (block * type)).

(** The temporary environment maps local temporaries to values. *)

Definition temp_env := PTree.t val.

(** [deref_loc ty m b ofs v] computes the value of a datum
  of type [ty] residing in memory [m] at block [b], offset [ofs].
  If the type [ty] indicates an access by value, the corresponding
  memory load is performed.  If the type [ty] indicates an access by
  reference or by copy, the pointer [Vptr b ofs] is returned. *)

Inductive deref_loc (ty: type) (m: mem) (b: block) (ofs: int) : val -> Prop :=
  | deref_loc_value: forall chunk v,
      access_mode ty = By_value chunk ->
      Mem.loadv chunk m (Vptr b ofs) = Some v ->
      deref_loc ty m b ofs v
  | deref_loc_reference:
      access_mode ty = By_reference ->
      deref_loc ty m b ofs (Vptr b ofs)
  | deref_loc_copy:
      access_mode ty = By_copy ->
      deref_loc ty m b ofs (Vptr b ofs).

(** Symmetrically, [assign_loc ty m b ofs v m'] returns the
  memory state after storing the value [v] in the datum
  of type [ty] residing in memory [m] at block [b], offset [ofs].
  This is allowed only if [ty] indicates an access by value or by copy.
  [m'] is the updated memory state. *)

Inductive assign_loc (ty: type) (m: mem) (b: block) (ofs: int):
                                            val -> mem -> Prop :=
  | assign_loc_value: forall v chunk m',
      access_mode ty = By_value chunk ->
      Mem.storev chunk m (Vptr b ofs) v = Some m' ->
      assign_loc ty m b ofs v m'
  | assign_loc_copy: forall b' ofs' bytes m',
      access_mode ty = By_copy ->
      (alignof ty | Int.unsigned ofs') -> (alignof ty | Int.unsigned ofs) ->
      b' <> b \/ Int.unsigned ofs' = Int.unsigned ofs
              \/ Int.unsigned ofs' + sizeof ty <= Int.unsigned ofs
              \/ Int.unsigned ofs + sizeof ty <= Int.unsigned ofs' ->
      Mem.loadbytes m b' (Int.unsigned ofs') (sizeof ty) = Some bytes ->
      Mem.storebytes m b (Int.unsigned ofs) bytes = Some m' ->
      assign_loc ty m b ofs (Vptr b' ofs') m'.

(** Initialization of local variables that are parameters to a function.
  [bind_parameters e m1 params args m2] stores the values [args]
  in the memory blocks corresponding to the variables [params].
  [m1] is the initial memory state and [m2] the final memory state. *)

Inductive bind_parameters (e: env):
                           mem -> list (ident * type) -> list val ->
                           mem -> Prop :=
  | bind_parameters_nil:
      forall m,
      bind_parameters e m nil nil m
  | bind_parameters_cons:
      forall m id ty params v1 vl b m1 m2,
      PTree.get id e = Some(b, ty) ->
      assign_loc ty m b Int.zero v1 m1 ->
      bind_parameters e m1 params vl m2 ->
      bind_parameters e m ((id, ty) :: params) (v1 :: vl) m2.

(** Initialization of temporary variables *)

Fixpoint create_undef_temps (temps: list (ident * type)) : temp_env :=
  match temps with
  | nil => PTree.empty val
  | (id, t) :: temps' => PTree.set id Vundef (create_undef_temps temps')
 end.

(** Optional assignment to a temporary *)

Definition set_opttemp (optid: option ident) (v: val) (le: temp_env) :=
  match optid with
  | None => le
  | Some id => PTree.set id v le
  end.

(** Selection of the appropriate case of a [switch], given the value [n]
  of the selector expression. *)

Fixpoint select_switch (n: int) (sl: labeled_statements)
                       {struct sl}: labeled_statements :=
  match sl with
  | LSdefault _ => sl
  | LScase c s sl' => if Int.eq c n then sl else select_switch n sl'
  end.

(** Turn a labeled statement into a sequence *)

Fixpoint seq_of_labeled_statement (sl: labeled_statements) : statement :=
  match sl with
  | LSdefault s => s
  | LScase c s sl' => Ssequence s (seq_of_labeled_statement sl')
  end.

Section SEMANTICS.

Variable ge: genv.

(** [type_of_global b] returns the type of the global variable or function
  at address [b]. *)

Definition type_of_global (b: block) : option type :=
  match Genv.find_var_info ge b with
  | Some gv => Some gv.(gvar_info)
  | None =>
      match Genv.find_funct_ptr ge b with
      | Some fd => Some(type_of_fundef fd)
      | None => None
      end
  end.

(** ** Evaluation of expressions *)

Section EXPR.

Variable e: env.
Variable le: temp_env.
Variable m: mem.

(** [eval_expr ge e m a v] defines the evaluation of expression [a]
  in r-value position.  [v] is the value of the expression.
  [e] is the current environment and [m] is the current memory state. *)

Inductive eval_expr: expr -> val -> Prop :=
  | eval_Econst_int:   forall i ty,
      eval_expr (Econst_int i ty) (Vint i)
  | eval_Econst_float:   forall f ty,
      eval_expr (Econst_float f ty) (Vfloat f)
  | eval_Etempvar:  forall id ty v,
      le!id = Some v ->
      eval_expr (Etempvar id ty) v
  | eval_Eaddrof: forall a ty loc ofs,
      eval_lvalue a loc ofs ->
      eval_expr (Eaddrof a ty) (Vptr loc ofs)
  | eval_Eunop:  forall op a ty v1 v,
      eval_expr a v1 ->
      sem_unary_operation op v1 (typeof a) = Some v ->
      eval_expr (Eunop op a ty) v
  | eval_Ebinop: forall op a1 a2 ty v1 v2 v,
      eval_expr a1 v1 ->
      eval_expr a2 v2 ->
      sem_binary_operation op v1 (typeof a1) v2 (typeof a2) m = Some v ->
      eval_expr (Ebinop op a1 a2 ty) v
  | eval_Ecast:   forall a ty v1 v,
      eval_expr a v1 ->
      sem_cast v1 (typeof a) ty = Some v ->
      eval_expr (Ecast a ty) v
  | eval_Elvalue: forall a loc ofs v,
      eval_lvalue a loc ofs -> 
      deref_loc (typeof a) m loc ofs v ->
      eval_expr a v

(** [eval_lvalue ge e m a b ofs] defines the evaluation of expression [a]
  in l-value position.  The result is the memory location [b, ofs]
  that contains the value of the expression [a]. *)

with eval_lvalue: expr -> block -> int -> Prop :=
  | eval_Evar_local:   forall id l ty,
      e!id = Some(l, ty) ->
      eval_lvalue (Evar id ty) l Int.zero
  | eval_Evar_global: forall id l ty,
      e!id = None ->
      Genv.find_symbol ge id = Some l ->
      type_of_global l = Some ty ->
      eval_lvalue (Evar id ty) l Int.zero
  | eval_Ederef: forall a ty l ofs,
      eval_expr a (Vptr l ofs) ->
      eval_lvalue (Ederef a ty) l ofs
 | eval_Efield_struct:   forall a i ty l ofs id fList att delta,
      eval_expr a (Vptr l ofs) ->
      typeof a = Tstruct id fList att ->
      field_offset i fList = OK delta ->
      eval_lvalue (Efield a i ty) l (Int.add ofs (Int.repr delta))
 | eval_Efield_union:   forall a i ty l ofs id fList att,
      eval_expr a (Vptr l ofs) ->
      typeof a = Tunion id fList att ->
      eval_lvalue (Efield a i ty) l ofs.

Scheme eval_expr_ind2 := Minimality for eval_expr Sort Prop
  with eval_lvalue_ind2 := Minimality for eval_lvalue Sort Prop.
Combined Scheme eval_expr_lvalue_ind from eval_expr_ind2, eval_lvalue_ind2.

(** [eval_exprlist ge e m al tyl vl] evaluates a list of r-value
  expressions [al], cast their values to the types given in [tyl],
  and produces the list of cast values [vl].  It is used to
  evaluate the arguments of function calls. *)

Inductive eval_exprlist: list expr -> typelist -> list val -> Prop :=
  | eval_Enil:
      eval_exprlist nil Tnil nil
  | eval_Econs:   forall a bl ty tyl v1 v2 vl,
      eval_expr a v1 ->
      sem_cast v1 (typeof a) ty = Some v2 ->
      eval_exprlist bl tyl vl ->
      eval_exprlist (a :: bl) (Tcons ty tyl) (v2 :: vl).

End EXPR.

(** ** Transition semantics for statements and functions *)

(** Continuations *)

Inductive cont: Type :=
  | Kstop: cont
  | Kseq: statement -> cont -> cont       (**r [Kseq s2 k] = after [s1] in [s1;s2] *)
  | Kloop1: statement -> statement -> cont -> cont (**r [Kloop1 s1 s2 k] = after [s1] in [Sloop s1 s2] *)
  | Kloop2: statement -> statement -> cont -> cont (**r [Kloop1 s1 s2 k] = after [s2] in [Sloop s1 s2] *)
  | Kswitch: cont -> cont       (**r catches [break] statements arising out of [switch] *)
  | Kcall: option ident ->                  (**r where to store result *)
           function ->                      (**r calling function *)
           env ->                           (**r local env of calling function *)
           temp_env ->                      (**r temporary env of calling function *)
           cont -> cont.

(** Pop continuation until a call or stop *)

Fixpoint call_cont (k: cont) : cont :=
  match k with
  | Kseq s k => call_cont k
  | Kloop1 s1 s2 k => call_cont k
  | Kloop2 s1 s2 k => call_cont k
  | Kswitch k => call_cont k
  | _ => k
  end.

Definition is_call_cont (k: cont) : Prop :=
  match k with
  | Kstop => True
  | Kcall _ _ _ _ _ => True
  | _ => False
  end.

(** States *)

Inductive state: Type :=
  | State
      (f: function)
      (s: statement)
      (k: cont)
      (e: env)
      (le: temp_env)
      (m: mem) : state
  | Callstate
      (fd: fundef)
      (args: list val)
      (k: cont)
      (m: mem) : state
  | Returnstate
      (res: val)
      (k: cont)
      (m: mem) : state.
                 
(** Find the statement and manufacture the continuation 
  corresponding to a label *)

Fixpoint find_label (lbl: label) (s: statement) (k: cont) 
                    {struct s}: option (statement * cont) :=
  match s with
  | Ssequence s1 s2 =>
      match find_label lbl s1 (Kseq s2 k) with
      | Some sk => Some sk
      | None => find_label lbl s2 k
      end
  | Sifthenelse a s1 s2 =>
      match find_label lbl s1 k with
      | Some sk => Some sk
      | None => find_label lbl s2 k
      end
  | Sloop s1 s2 =>
      match find_label lbl s1 (Kloop1 s1 s2 k) with
      | Some sk => Some sk
      | None => find_label lbl s2 (Kloop2 s1 s2 k)
      end
  | Sswitch e sl =>
      find_label_ls lbl sl (Kswitch k)
  | Slabel lbl' s' =>
      if ident_eq lbl lbl' then Some(s', k) else find_label lbl s' k
  | _ => None
  end

with find_label_ls (lbl: label) (sl: labeled_statements) (k: cont) 
                    {struct sl}: option (statement * cont) :=
  match sl with
  | LSdefault s => find_label lbl s k
  | LScase _ s sl' =>
      match find_label lbl s (Kseq (seq_of_labeled_statement sl') k) with
      | Some sk => Some sk
      | None => find_label_ls lbl sl' k
      end
  end.

(** Transition relation *)

Inductive step: state -> trace -> state -> Prop :=

  | step_assign:   forall f a1 a2 k e le m loc ofs v2 v m',
      eval_lvalue e le m a1 loc ofs ->
      eval_expr e le m a2 v2 ->
      sem_cast v2 (typeof a2) (typeof a1) = Some v ->
      assign_loc (typeof a1) m loc ofs v m' ->
      step (State f (Sassign a1 a2) k e le m)
        E0 (State f Sskip k e le m')

  | step_set:   forall f id a k e le m v,
      eval_expr e le m a v ->
      step (State f (Sset id a) k e le m)
        E0 (State f Sskip k e (PTree.set id v le) m)

  | step_call:   forall f optid a al k e le m tyargs tyres vf vargs fd,
      classify_fun (typeof a) = fun_case_f tyargs tyres ->
      eval_expr e le m a vf ->
      eval_exprlist e le m al tyargs vargs ->
      Genv.find_funct ge vf = Some fd ->
      type_of_fundef fd = Tfunction tyargs tyres ->
      step (State f (Scall optid a al) k e le m)
        E0 (Callstate fd vargs (Kcall optid f e le k) m)

  | step_builtin:   forall f optid ef tyargs al k e le m vargs t vres m',
      eval_exprlist e le m al tyargs vargs ->
      external_call ef ge vargs m t vres m' ->
      step (State f (Sbuiltin optid ef tyargs al) k e le m)
         t (State f Sskip k e (set_opttemp optid vres le) m')

  | step_seq:  forall f s1 s2 k e le m,
      step (State f (Ssequence s1 s2) k e le m)
        E0 (State f s1 (Kseq s2 k) e le m)
  | step_skip_seq: forall f s k e le m,
      step (State f Sskip (Kseq s k) e le m)
        E0 (State f s k e le m)
  | step_continue_seq: forall f s k e le m,
      step (State f Scontinue (Kseq s k) e le m)
        E0 (State f Scontinue k e le m)
  | step_break_seq: forall f s k e le m,
      step (State f Sbreak (Kseq s k) e le m)
        E0 (State f Sbreak k e le m)

  | step_ifthenelse:  forall f a s1 s2 k e le m v1 b,
      eval_expr e le m a v1 ->
      bool_val v1 (typeof a) = Some b ->
      step (State f (Sifthenelse a s1 s2) k e le m)
        E0 (State f (if b then s1 else s2) k e le m)

  | step_loop: forall f s1 s2 k e le m,
      step (State f (Sloop s1 s2) k e le m)
        E0 (State f s1 (Kloop1 s1 s2 k) e le m)
  | step_skip_or_continue_loop1:  forall f s1 s2 k e le m x,
      x = Sskip \/ x = Scontinue ->
      step (State f x (Kloop1 s1 s2 k) e le m)
        E0 (State f s2 (Kloop2 s1 s2 k) e le m)
  | step_break_loop1:  forall f s1 s2 k e le m,
      step (State f Sbreak (Kloop1 s1 s2 k) e le m)
        E0 (State f Sskip k e le m)
  | step_skip_loop2: forall f s1 s2 k e le m,
      step (State f Sskip (Kloop2 s1 s2 k) e le m)
        E0 (State f (Sloop s1 s2) k e le m)
  | step_break_loop2: forall f s1 s2 k e le m,
      step (State f Sbreak (Kloop2 s1 s2 k) e le m)
        E0 (State f Sskip k e le m)

  | step_return_0: forall f k e le m m',
      Mem.free_list m (blocks_of_env e) = Some m' ->
      step (State f (Sreturn None) k e le m)
        E0 (Returnstate Vundef (call_cont k) m')
  | step_return_1: forall f a k e le m v v' m',
      eval_expr e le m a v -> 
      sem_cast v (typeof a) f.(fn_return) = Some v' ->
      Mem.free_list m (blocks_of_env e) = Some m' ->
      step (State f (Sreturn (Some a)) k e le m)
        E0 (Returnstate v' (call_cont k) m')
  | step_skip_call: forall f k e le m m',
      is_call_cont k ->
      f.(fn_return) = Tvoid ->
      Mem.free_list m (blocks_of_env e) = Some m' ->
      step (State f Sskip k e le m)
        E0 (Returnstate Vundef k m')

  | step_switch: forall f a sl k e le m n,
      eval_expr e le m a (Vint n) ->
      step (State f (Sswitch a sl) k e le m)
        E0 (State f (seq_of_labeled_statement (select_switch n sl)) (Kswitch k) e le m)
  | step_skip_break_switch: forall f x k e le m,
      x = Sskip \/ x = Sbreak ->
      step (State f x (Kswitch k) e le m)
        E0 (State f Sskip k e le m)
  | step_continue_switch: forall f k e le m,
      step (State f Scontinue (Kswitch k) e le m)
        E0 (State f Scontinue k e le m)

  | step_label: forall f lbl s k e le m,
      step (State f (Slabel lbl s) k e le m)
        E0 (State f s k e le m)

  | step_goto: forall f lbl k e le m s' k',
      find_label lbl f.(fn_body) (call_cont k) = Some (s', k') ->
      step (State f (Sgoto lbl) k e le m)
        E0 (State f s' k' e le m)

  | step_internal_function: forall f vargs k m e m1 m2,
      list_norepet (var_names f.(fn_params) ++ var_names f.(fn_vars)) ->
      alloc_variables empty_env m (f.(fn_params) ++ f.(fn_vars)) e m1 ->
      bind_parameters e m1 f.(fn_params) vargs m2 ->
      step (Callstate (Internal f) vargs k m)
        E0 (State f f.(fn_body) k e (create_undef_temps f.(fn_temps)) m2)

  | step_external_function: forall ef targs tres vargs k m vres t m',
      external_call ef ge vargs m t vres m' ->
      step (Callstate (External ef targs tres) vargs k m)
         t (Returnstate vres k m')

  | step_returnstate: forall v optid f e le k m,
      step (Returnstate v (Kcall optid f e le k) m)
        E0 (State f Sskip k e (set_opttemp optid v le) m).

(** ** Whole-program semantics *)

(** Execution of whole programs are described as sequences of transitions
  from an initial state to a final state.  An initial state is a [Callstate]
  corresponding to the invocation of the ``main'' function of the program
  without arguments and with an empty continuation. *)

Inductive initial_state (p: program): state -> Prop :=
  | initial_state_intro: forall b f m0,
      let ge := Genv.globalenv p in
      Genv.init_mem p = Some m0 ->
      Genv.find_symbol ge p.(prog_main) = Some b ->
      Genv.find_funct_ptr ge b = Some f ->
      type_of_fundef f = Tfunction Tnil type_int32s ->
      initial_state p (Callstate f nil Kstop m0).

(** A final state is a [Returnstate] with an empty continuation. *)

Inductive final_state: state -> int -> Prop :=
  | final_state_intro: forall r m,
      final_state (Returnstate (Vint r) Kstop m) r.

End SEMANTICS.

(** Wrapping up these definitions in a small-step semantics. *)

Definition semantics (p: program) :=
  Semantics step (initial_state p) final_state (Genv.globalenv p).

(** This semantics is receptive to changes in events. *)

Lemma semantics_receptive:
  forall (p: program), receptive (semantics p).
Proof.
  intros. constructor; simpl; intros.
(* receptiveness *)
  assert (t1 = E0 -> exists s2, step (Genv.globalenv p) s t2 s2).
    intros. subst. inv H0. exists s1; auto.
  inversion H; subst; auto.
  (* builtin *)
  exploit external_call_receptive; eauto. intros [vres2 [m2 EC2]]. 
  econstructor; econstructor; eauto.
  (* external *)
  exploit external_call_receptive; eauto. intros [vres2 [m2 EC2]]. 
  exists (Returnstate vres2 k m2). econstructor; eauto.
(* trace length *)
  red; intros. inv H; simpl; try omega.
  eapply external_call_trace_length; eauto.
  eapply external_call_trace_length; eauto.
Qed.

(** * Alternate big-step semantics *)

Section BIGSTEP.

Variable ge: genv.

(** ** Big-step semantics for terminating statements and functions *)

(** The execution of a statement produces an ``outcome'', indicating
  how the execution terminated: either normally or prematurely
  through the execution of a [break], [continue] or [return] statement. *)

Inductive outcome: Type :=
   | Out_break: outcome                 (**r terminated by [break] *)
   | Out_continue: outcome              (**r terminated by [continue] *)
   | Out_normal: outcome                (**r terminated normally *)
   | Out_return: option (val * type) -> outcome. (**r terminated by [return] *)

Inductive out_normal_or_continue : outcome -> Prop :=
  | Out_normal_or_continue_N: out_normal_or_continue Out_normal
  | Out_normal_or_continue_C: out_normal_or_continue Out_continue.

Inductive out_break_or_return : outcome -> outcome -> Prop :=
  | Out_break_or_return_B: out_break_or_return Out_break Out_normal
  | Out_break_or_return_R: forall ov,
      out_break_or_return (Out_return ov) (Out_return ov).

Definition outcome_switch (out: outcome) : outcome :=
  match out with
  | Out_break => Out_normal
  | o => o
  end.

Definition outcome_result_value (out: outcome) (t: type) (v: val) : Prop :=
  match out, t with
  | Out_normal, Tvoid => v = Vundef
  | Out_return None, Tvoid => v = Vundef
  | Out_return (Some (v',t')), ty => ty <> Tvoid /\ sem_cast v' t' t = Some v
  | _, _ => False
  end. 

(** [exec_stmt ge e m1 s t m2 out] describes the execution of 
  the statement [s].  [out] is the outcome for this execution.
  [m1] is the initial memory state, [m2] the final memory state.
  [t] is the trace of input/output events performed during this
  evaluation. *)

Inductive exec_stmt: env -> temp_env -> mem -> statement -> trace -> temp_env -> mem -> outcome -> Prop :=
  | exec_Sskip:   forall e le m,
      exec_stmt e le m Sskip
               E0 le m Out_normal
  | exec_Sassign:   forall e le m a1 a2 loc ofs v2 v m',
      eval_lvalue ge e le m a1 loc ofs ->
      eval_expr ge e le m a2 v2 ->
      sem_cast v2 (typeof a2) (typeof a1) = Some v ->
      assign_loc (typeof a1) m loc ofs v m' ->
      exec_stmt e le m (Sassign a1 a2)
               E0 le m' Out_normal
  | exec_Sset:     forall e le m id a v,
      eval_expr ge e le m a v ->
      exec_stmt e le m (Sset id a)
               E0 (PTree.set id v le) m Out_normal 
  | exec_Scall:   forall e le m optid a al tyargs tyres vf vargs f t m' vres,
      classify_fun (typeof a) = fun_case_f tyargs tyres ->
      eval_expr ge e le m a vf ->
      eval_exprlist ge e le m al tyargs vargs ->
      Genv.find_funct ge vf = Some f ->
      type_of_fundef f = Tfunction tyargs tyres ->
      eval_funcall m f vargs t m' vres ->
      exec_stmt e le m (Scall optid a al)
                t (set_opttemp optid vres le) m' Out_normal
  | exec_Sbuiltin:   forall e le m optid ef al tyargs vargs t m' vres,
      eval_exprlist ge e le m al tyargs vargs ->
      external_call ef ge vargs m t vres m' ->
      exec_stmt e le m (Sbuiltin optid ef tyargs al)
                t (set_opttemp optid vres le) m' Out_normal
  | exec_Sseq_1:   forall e le m s1 s2 t1 le1 m1 t2 le2 m2 out,
      exec_stmt e le m s1 t1 le1 m1 Out_normal ->
      exec_stmt e le1 m1 s2 t2 le2 m2 out ->
      exec_stmt e le m (Ssequence s1 s2)
                (t1 ** t2) le2 m2 out
  | exec_Sseq_2:   forall e le m s1 s2 t1 le1 m1 out,
      exec_stmt e le m s1 t1 le1 m1 out ->
      out <> Out_normal ->
      exec_stmt e le m (Ssequence s1 s2)
                t1 le1 m1 out
  | exec_Sifthenelse: forall e le m a s1 s2 v1 b t le' m' out,
      eval_expr ge e le m a v1 ->
      bool_val v1 (typeof a) = Some b ->
      exec_stmt e le m (if b then s1 else s2) t le' m' out ->
      exec_stmt e le m (Sifthenelse a s1 s2)
                t le' m' out
  | exec_Sreturn_none:   forall e le m,
      exec_stmt e le m (Sreturn None)
               E0 le m (Out_return None)
  | exec_Sreturn_some: forall e le m a v,
      eval_expr ge e le m a v ->
      exec_stmt e le m (Sreturn (Some a))
                E0 le m (Out_return (Some (v, typeof a)))
  | exec_Sbreak:   forall e le m,
      exec_stmt e le m Sbreak
               E0 le m Out_break
  | exec_Scontinue:   forall e le m,
      exec_stmt e le m Scontinue
               E0 le m Out_continue
  | exec_Sloop_stop1: forall e le m s1 s2 t le' m' out' out,
      exec_stmt e le m s1 t le' m' out' ->
      out_break_or_return out' out ->
      exec_stmt e le m (Sloop s1 s2)
                t le' m' out
  | exec_Sloop_stop2: forall e le m s1 s2 t1 le1 m1 out1 t2 le2 m2 out2 out,
      exec_stmt e le m s1 t1 le1 m1 out1 ->
      out_normal_or_continue out1 ->
      exec_stmt e le1 m1 s2 t2 le2 m2 out2 ->
      out_break_or_return out2 out ->
      exec_stmt e le m (Sloop s1 s2)
                (t1**t2) le2 m2 out
  | exec_Sloop_loop: forall e le m s1 s2 t1 le1 m1 out1 t2 le2 m2 t3 le3 m3 out,
      exec_stmt e le m s1 t1 le1 m1 out1 ->
      out_normal_or_continue out1 ->
      exec_stmt e le1 m1 s2 t2 le2 m2 Out_normal ->
      exec_stmt e le2 m2 (Sloop s1 s2) t3 le3 m3 out ->
      exec_stmt e le m (Sloop s1 s2)
                (t1**t2**t3) le3 m3 out
  | exec_Sswitch:   forall e le m a t n sl le1 m1 out,
      eval_expr ge e le m a (Vint n) ->
      exec_stmt e le m (seq_of_labeled_statement (select_switch n sl)) t le1 m1 out ->
      exec_stmt e le m (Sswitch a sl)
                t le1 m1 (outcome_switch out)

(** [eval_funcall m1 fd args t m2 res] describes the invocation of
  function [fd] with arguments [args].  [res] is the value returned
  by the call.  *)

with eval_funcall: mem -> fundef -> list val -> trace -> mem -> val -> Prop :=
  | eval_funcall_internal: forall le m f vargs t e m1 m2 m3 out vres m4,
      alloc_variables empty_env m (f.(fn_params) ++ f.(fn_vars)) e m1 ->
      list_norepet (var_names f.(fn_params) ++ var_names f.(fn_vars)) ->
      bind_parameters e m1 f.(fn_params) vargs m2 ->
      exec_stmt e (create_undef_temps f.(fn_temps)) m2 f.(fn_body) t le m3 out ->
      outcome_result_value out f.(fn_return) vres ->
      Mem.free_list m3 (blocks_of_env e) = Some m4 ->
      eval_funcall m (Internal f) vargs t m4 vres
  | eval_funcall_external: forall m ef targs tres vargs t vres m',
      external_call ef ge vargs m t vres m' ->
      eval_funcall m (External ef targs tres) vargs t m' vres.

Scheme exec_stmt_ind2 := Minimality for exec_stmt Sort Prop
  with eval_funcall_ind2 := Minimality for eval_funcall Sort Prop.
Combined Scheme exec_stmt_funcall_ind from exec_stmt_ind2, eval_funcall_ind2.

(** ** Big-step semantics for diverging statements and functions *)

(** Coinductive semantics for divergence.
  [execinf_stmt ge e m s t] holds if the execution of statement [s]
  diverges, i.e. loops infinitely.  [t] is the possibly infinite
  trace of observable events performed during the execution. *)

CoInductive execinf_stmt: env -> temp_env -> mem -> statement -> traceinf -> Prop :=
  | execinf_Scall:   forall e le m optid a al vf tyargs tyres vargs f t,
      classify_fun (typeof a) = fun_case_f tyargs tyres ->
      eval_expr ge e le m a vf ->
      eval_exprlist ge e le m al tyargs vargs ->
      Genv.find_funct ge vf = Some f ->
      type_of_fundef f = Tfunction tyargs tyres ->
      evalinf_funcall m f vargs t ->
      execinf_stmt e le m (Scall optid a al) t
  | execinf_Sseq_1:   forall e le m s1 s2 t,
      execinf_stmt e le m s1 t ->
      execinf_stmt e le m (Ssequence s1 s2) t
  | execinf_Sseq_2:   forall e le m s1 s2 t1 le1 m1 t2,
      exec_stmt e le m s1 t1 le1 m1 Out_normal ->
      execinf_stmt e le1 m1 s2 t2 ->
      execinf_stmt e le m (Ssequence s1 s2) (t1 *** t2)
  | execinf_Sifthenelse: forall e le m a s1 s2 v1 b t,
      eval_expr ge e le m a v1 ->
      bool_val v1 (typeof a) = Some b ->
      execinf_stmt e le m (if b then s1 else s2) t ->
      execinf_stmt e le m (Sifthenelse a s1 s2) t
  | execinf_Sloop_body1: forall e le m s1 s2 t,
      execinf_stmt e le m s1 t ->
      execinf_stmt e le m (Sloop s1 s2) t
  | execinf_Sloop_body2: forall e le m s1 s2 t1 le1 m1 out1 t2,
      exec_stmt e le m s1 t1 le1 m1 out1 ->
      out_normal_or_continue out1 ->
      execinf_stmt e le1 m1 s2 t2 ->
      execinf_stmt e le m (Sloop s1 s2) (t1***t2)
  | execinf_Sloop_loop: forall e le m s1 s2 t1 le1 m1 out1 t2 le2 m2 t3,
      exec_stmt e le m s1 t1 le1 m1 out1 ->
      out_normal_or_continue out1 ->
      exec_stmt e le1 m1 s2 t2 le2 m2 Out_normal ->
      execinf_stmt e le2 m2 (Sloop s1 s2) t3 ->
      execinf_stmt e le m (Sloop s1 s2) (t1***t2***t3)
  | execinf_Sswitch:   forall e le m a t n sl,
      eval_expr ge e le m a (Vint n) ->
      execinf_stmt e le m (seq_of_labeled_statement (select_switch n sl)) t ->
      execinf_stmt e le m (Sswitch a sl) t

(** [evalinf_funcall ge m fd args t] holds if the invocation of function
    [fd] on arguments [args] diverges, with observable trace [t]. *)

with evalinf_funcall: mem -> fundef -> list val -> traceinf -> Prop :=
  | evalinf_funcall_internal: forall m f vargs t e m1 m2,
      alloc_variables empty_env m (f.(fn_params) ++ f.(fn_vars)) e m1 ->
      list_norepet (var_names f.(fn_params) ++ var_names f.(fn_vars)) ->
      bind_parameters e m1 f.(fn_params) vargs m2 ->
      execinf_stmt e (create_undef_temps f.(fn_temps)) m2 f.(fn_body) t ->
      evalinf_funcall m (Internal f) vargs t.

End BIGSTEP.

(** Big-step execution of a whole program.  *)

Inductive bigstep_program_terminates (p: program): trace -> int -> Prop :=
  | bigstep_program_terminates_intro: forall b f m0 m1 t r,
      let ge := Genv.globalenv p in 
      Genv.init_mem p = Some m0 ->
      Genv.find_symbol ge p.(prog_main) = Some b ->
      Genv.find_funct_ptr ge b = Some f ->
      type_of_fundef f = Tfunction Tnil type_int32s ->
      eval_funcall ge m0 f nil t m1 (Vint r) ->
      bigstep_program_terminates p t r.

Inductive bigstep_program_diverges (p: program): traceinf -> Prop :=
  | bigstep_program_diverges_intro: forall b f m0 t,
      let ge := Genv.globalenv p in 
      Genv.init_mem p = Some m0 ->
      Genv.find_symbol ge p.(prog_main) = Some b ->
      Genv.find_funct_ptr ge b = Some f ->
      type_of_fundef f = Tfunction Tnil type_int32s ->
      evalinf_funcall ge m0 f nil t ->
      bigstep_program_diverges p t.

Definition bigstep_semantics (p: program) :=
  Bigstep_semantics (bigstep_program_terminates p) (bigstep_program_diverges p).

(** * Implication from big-step semantics to transition semantics *)

Section BIGSTEP_TO_TRANSITIONS.

Variable prog: program.
Let ge : genv := Genv.globalenv prog.

Inductive outcome_state_match
       (e: env) (le: temp_env) (m: mem) (f: function) (k: cont): outcome -> state -> Prop :=
  | osm_normal:
      outcome_state_match e le m f k Out_normal (State f Sskip k e le m)
  | osm_break:
      outcome_state_match e le m f k Out_break (State f Sbreak k e le m)
  | osm_continue:
      outcome_state_match e le m f k Out_continue (State f Scontinue k e le m)
  | osm_return_none: forall k',
      call_cont k' = call_cont k ->
      outcome_state_match e le m f k 
        (Out_return None) (State f (Sreturn None) k' e le m)
  | osm_return_some: forall a v k',
      call_cont k' = call_cont k ->
      eval_expr ge e le m a v ->
      outcome_state_match e le m f k
        (Out_return (Some (v,typeof a))) (State f (Sreturn (Some a)) k' e le m).

Lemma is_call_cont_call_cont:
  forall k, is_call_cont k -> call_cont k = k.
Proof.
  destruct k; simpl; intros; contradiction || auto.
Qed.

Lemma exec_stmt_eval_funcall_steps:
  (forall e le m s t le' m' out,
   exec_stmt ge e le m s t le' m' out ->
   forall f k, exists S,
   star step ge (State f s k e le m) t S
   /\ outcome_state_match e le' m' f k out S)
/\
  (forall m fd args t m' res,
   eval_funcall ge m fd args t m' res ->
   forall k,
   is_call_cont k ->
   star step ge (Callstate fd args k m) t (Returnstate res k m')).
Proof.
  apply exec_stmt_funcall_ind; intros.

(* skip *)
  econstructor; split. apply star_refl. constructor.

(* assign *)
  econstructor; split. apply star_one. econstructor; eauto. constructor.

(* set *)
  econstructor; split. apply star_one. econstructor; eauto. constructor.

(* call *)
  econstructor; split.
  eapply star_left. econstructor; eauto. 
  eapply star_right. apply H5. simpl; auto. econstructor. reflexivity. traceEq.
  constructor.

(* builtin *)
  econstructor; split. apply star_one. econstructor; eauto. constructor.

(* sequence 2 *)
  destruct (H0 f (Kseq s2 k)) as [S1 [A1 B1]]. inv B1.
  destruct (H2 f k) as [S2 [A2 B2]]. 
  econstructor; split.
  eapply star_left. econstructor.
  eapply star_trans. eexact A1. 
  eapply star_left. constructor. eexact A2.
  reflexivity. reflexivity. traceEq.
  auto.

(* sequence 1 *)
  destruct (H0 f (Kseq s2 k)) as [S1 [A1 B1]].
  set (S2 :=
    match out with
    | Out_break => State f Sbreak k e le1 m1
    | Out_continue => State f Scontinue k e le1 m1
    | _ => S1
    end).
  exists S2; split.
  eapply star_left. econstructor.
  eapply star_trans. eexact A1.
  unfold S2; inv B1.
    congruence.
    apply star_one. apply step_break_seq.
    apply star_one. apply step_continue_seq.
    apply star_refl.
    apply star_refl.
  reflexivity. traceEq.
  unfold S2; inv B1; congruence || econstructor; eauto.

(* ifthenelse *)
  destruct (H2 f k) as [S1 [A1 B1]].
  exists S1; split.
  eapply star_left. 2: eexact A1. eapply step_ifthenelse; eauto. traceEq.
  auto.

(* return none *)
  econstructor; split. apply star_refl. constructor. auto.

(* return some *)
  econstructor; split. apply star_refl. econstructor; eauto.

(* break *)
  econstructor; split. apply star_refl. constructor.

(* continue *)
  econstructor; split. apply star_refl. constructor.

(* loop stop 1 *)
  destruct (H0 f (Kloop1 s1 s2 k)) as [S1 [A1 B1]].
  set (S2 :=
    match out' with
    | Out_break => State f Sskip k e le' m'
    | _ => S1
    end).
  exists S2; split.
  eapply star_left. eapply step_loop. 
  eapply star_trans. eexact A1.
  unfold S2. inversion H1; subst.
  inv B1. apply star_one. constructor.    
  apply star_refl.
  reflexivity. traceEq.
  unfold S2. inversion H1; subst. constructor. inv B1; econstructor; eauto.

(* loop stop 2 *)
  destruct (H0 f (Kloop1 s1 s2 k)) as [S1 [A1 B1]].
  destruct (H3 f (Kloop2 s1 s2 k)) as [S2 [A2 B2]].
  set (S3 :=
    match out2 with
    | Out_break => State f Sskip k e le2 m2
    | _ => S2
    end).
  exists S3; split.
  eapply star_left. eapply step_loop. 
  eapply star_trans. eexact A1.
  eapply star_left with (s2 := State f s2 (Kloop2 s1 s2 k) e le1 m1).
  inv H1; inv B1; constructor; auto.
  eapply star_trans. eexact A2.
  unfold S3. inversion H4; subst.
  inv B2. apply star_one. constructor. apply star_refl.
  reflexivity. reflexivity. reflexivity. traceEq. 
  unfold S3. inversion H4; subst. constructor. inv B2; econstructor; eauto.

(* loop loop *)
  destruct (H0 f (Kloop1 s1 s2 k)) as [S1 [A1 B1]].
  destruct (H3 f (Kloop2 s1 s2 k)) as [S2 [A2 B2]].
  destruct (H5 f k) as [S3 [A3 B3]].
  exists S3; split.
  eapply star_left. eapply step_loop. 
  eapply star_trans. eexact A1.
  eapply star_left with (s2 := State f s2 (Kloop2 s1 s2 k) e le1 m1).
  inv H1; inv B1; constructor; auto.
  eapply star_trans. eexact A2.
  eapply star_left with (s2 := State f (Sloop s1 s2) k e le2 m2).
  inversion H4; subst; inv B2; constructor; auto. 
  eexact A3.
  reflexivity. reflexivity. reflexivity. reflexivity. traceEq. 
  auto.

(* switch *)
  destruct (H1 f (Kswitch k)) as [S1 [A1 B1]].
  set (S2 :=
    match out with
    | Out_normal => State f Sskip k e le1 m1
    | Out_break => State f Sskip k e le1 m1
    | Out_continue => State f Scontinue k e le1 m1
    | _ => S1
    end).
  exists S2; split.
  eapply star_left. eapply step_switch; eauto. 
  eapply star_trans. eexact A1. 
  unfold S2; inv B1. 
    apply star_one. constructor. auto. 
    apply star_one. constructor. auto. 
    apply star_one. constructor. 
    apply star_refl.
    apply star_refl.
  reflexivity. traceEq.
  unfold S2. inv B1; simpl; econstructor; eauto.

(* call internal *)
  destruct (H3 f k) as [S1 [A1 B1]].
  eapply star_left. eapply step_internal_function; eauto.
  eapply star_right. eexact A1. 
   inv B1; simpl in H4; try contradiction.
  (* Out_normal *)
  assert (fn_return f = Tvoid /\ vres = Vundef).
    destruct (fn_return f); auto || contradiction.
  destruct H7. subst vres. apply step_skip_call; auto.
  (* Out_return None *)
  assert (fn_return f = Tvoid /\ vres = Vundef).
    destruct (fn_return f); auto || contradiction.
  destruct H8. subst vres.
  rewrite <- (is_call_cont_call_cont k H6). rewrite <- H7.
  apply step_return_0; auto.
  (* Out_return Some *)
  destruct H4.
  rewrite <- (is_call_cont_call_cont k H6). rewrite <- H7.
  eapply step_return_1; eauto.
  reflexivity. traceEq.

(* call external *)
  apply star_one. apply step_external_function; auto. 
Qed.

Lemma exec_stmt_steps:
   forall e le m s t le' m' out,
   exec_stmt ge e le m s t le' m' out ->
   forall f k, exists S,
   star step ge (State f s k e le m) t S
   /\ outcome_state_match e le' m' f k out S.
Proof (proj1 exec_stmt_eval_funcall_steps).

Lemma eval_funcall_steps:
   forall m fd args t m' res,
   eval_funcall ge m fd args t m' res ->
   forall k,
   is_call_cont k ->
   star step ge (Callstate fd args k m) t (Returnstate res k m').
Proof (proj2 exec_stmt_eval_funcall_steps).

Definition order (x y: unit) := False.

Lemma evalinf_funcall_forever:
  forall m fd args T k,
  evalinf_funcall ge m fd args T ->
  forever_N step order ge tt (Callstate fd args k m) T.
Proof.
  cofix CIH_FUN.
  assert (forall e le m s T f k,
          execinf_stmt ge e le m s T ->
          forever_N step order ge tt (State f s k e le m) T).
  cofix CIH_STMT.
  intros. inv H.

(* call  *)
  eapply forever_N_plus.
  apply plus_one. eapply step_call; eauto. 
  eapply CIH_FUN. eauto. traceEq.

(* seq 1 *)
  eapply forever_N_plus.
  apply plus_one. econstructor.
  apply CIH_STMT; eauto. traceEq.
(* seq 2 *)
  destruct (exec_stmt_steps _ _ _ _ _ _ _ _ H0 f (Kseq s2 k)) as [S1 [A1 B1]].
  inv B1.
  eapply forever_N_plus.
  eapply plus_left. constructor. eapply star_trans. eexact A1. 
  apply star_one. constructor. reflexivity. reflexivity.
  apply CIH_STMT; eauto. traceEq.

(* ifthenelse *)
  eapply forever_N_plus.
  apply plus_one. eapply step_ifthenelse with (b := b); eauto. 
  apply CIH_STMT; eauto. traceEq.

(* loop body 1 *)
  eapply forever_N_plus.
  eapply plus_one. constructor. 
  apply CIH_STMT; eauto. traceEq.
(* loop body 2 *)
  destruct (exec_stmt_steps _ _ _ _ _ _ _ _ H0 f (Kloop1 s1 s2 k)) as [S1 [A1 B1]].
  eapply forever_N_plus with (s2 := State f s2 (Kloop2 s1 s2 k) e le1 m1).
  eapply plus_left. constructor.
  eapply star_right. eexact A1.
  inv H1; inv B1; constructor; auto. 
  reflexivity. reflexivity.
  apply CIH_STMT; eauto. traceEq.
(* loop loop *)
  destruct (exec_stmt_steps _ _ _ _ _ _ _ _ H0 f (Kloop1 s1 s2 k)) as [S1 [A1 B1]].
  destruct (exec_stmt_steps _ _ _ _ _ _ _ _ H2 f (Kloop2 s1 s2 k)) as [S2 [A2 B2]].
  eapply forever_N_plus with (s2 := State f (Sloop s1 s2) k e le2 m2).
  eapply plus_left. constructor.
  eapply star_trans. eexact A1.
  eapply star_left. inv H1; inv B1; constructor; auto.
  eapply star_right. eexact A2.
  inv B2. constructor.
  reflexivity. reflexivity. reflexivity. reflexivity.
  apply CIH_STMT; eauto. traceEq.

(* switch *)
  eapply forever_N_plus.
  eapply plus_one. eapply step_switch; eauto.
  apply CIH_STMT; eauto.
  traceEq.

(* call internal *)
  intros. inv H0.
  eapply forever_N_plus.
  eapply plus_one. econstructor; eauto. 
  apply H; eauto.
  traceEq.
Qed.

Theorem bigstep_semantics_sound:
  bigstep_sound (bigstep_semantics prog) (semantics prog).
Proof.
  constructor; simpl; intros.
(* termination *)
  inv H. econstructor; econstructor.
  split. econstructor; eauto.
  split. eapply eval_funcall_steps. eauto. red; auto. 
  econstructor.
(* divergence *)
  inv H. econstructor.
  split. econstructor; eauto.
  eapply forever_N_forever with (order := order).
  red; intros. constructor; intros. red in H. elim H.
  eapply evalinf_funcall_forever; eauto. 
Qed.

End BIGSTEP_TO_TRANSITIONS.