(* *********************************************************************)
(*                                                                     *)
(*              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.     *)
(*                                                                     *)
(* *********************************************************************)
(** Dynamic semantics for the Compcert C language *)
(** * 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].) It also contains a composite environment, used by type-dependent operations. *)
Record genv := { genv_genv :> Genv.t fundef type; genv_cenv :> composite_env }.
Definition globalenv (p: program) :=
{| genv_genv := Genv.globalenv p; genv_cenv := p.(prog_comp_env) |}.
(** 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)).
Section SEMANTICS.
Variable ge: genv.
(** [deref_loc ty m b ofs t 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, the pointer [Vptr b ofs] is returned.  [v] is the value returned, and [t] the trace of observables (nonempty if this is a volatile access). *)
Inductive deref_loc (ty: type) (m: mem) (b: block) (ofs: ptrofs) : trace -> val -> Prop :=
| deref_loc_value: forall chunk v,
access_mode ty = By_value chunk ->
type_is_volatile ty = false ->
Mem.loadv chunk m (Vptr b ofs) = Some v ->
deref_loc ty m b ofs E0 v
| deref_loc_volatile: forall chunk t v,
access_mode ty = By_value chunk -> type_is_volatile ty = true ->
volatile_load ge chunk m b ofs t v ->
deref_loc ty m b ofs t v
| deref_loc_reference:
access_mode ty = By_reference ->
deref_loc ty m b ofs E0 (Vptr b ofs)
| deref_loc_copy:
access_mode ty = By_copy ->
deref_loc ty m b ofs E0 (Vptr b ofs).
(** Symmetrically, [assign_loc ty m b ofs v t 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 and [t] the trace of observables (nonempty if this is a volatile store). *)
Inductive assign_loc (ty: type) (m: mem) (b: block) (ofs: ptrofs):
val -> trace -> mem -> Prop :=
| assign_loc_value: forall v chunk m',
access_mode ty = By_value chunk ->
type_is_volatile ty = false ->
Mem.storev chunk m (Vptr b ofs) v = Some m' ->
assign_loc ty m b ofs v E0 m'
| assign_loc_volatile: forall v chunk t m',
access_mode ty = By_value chunk -> type_is_volatile ty = true ->
volatile_store ge chunk m b ofs v t m' ->
assign_loc ty m b ofs v t m'
| assign_loc_copy: forall b' ofs' bytes m',
access_mode ty = By_copy ->
(alignof_blockcopy ge ty | Ptrofs.unsigned ofs') ->
(alignof_blockcopy ge ty | Ptrofs.unsigned ofs) ->
b' <> b \/ Ptrofs.unsigned ofs' = Ptrofs.unsigned ofs
\/ Ptrofs.unsigned ofs' + sizeof ge ty <= Ptrofs.unsigned ofs
\/ Ptrofs.unsigned ofs + sizeof ge ty <= Ptrofs.unsigned ofs' ->
Mem.loadbytes m b' (Ptrofs.unsigned ofs') (sizeof ge ty) = Some bytes ->
Mem.storebytes m b (Ptrofs.unsigned ofs) bytes = Some m' ->
assign_loc ty m b ofs (Vptr b' ofs') E0 m'.
(** Allocation of function-local variables. [alloc_variables e1 m1 vars e2 m2] allocates one memory block for each variable declared in [vars], and associates the variable name with this block.  [e1] and [m1] are the initial local environment and memory state.  [e2] and [m2] are the final local environment and memory state. *)
Inductive alloc_variables: env -> mem ->
list (ident * type) ->
env -> mem -> Prop :=
| alloc_variables_nil:
forall e m,
alloc_variables e m nil e m
| alloc_variables_cons:
forall e m id ty vars m1 b1 m2 e2,
Mem.alloc m 0 (sizeof ge ty) = (m1, b1) ->
alloc_variables (PTree.set id (b1, ty) e) m1 vars e2 m2 ->
alloc_variables e m ((id, ty) :: vars) e2 m2.
(** 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 Ptrofs.zero v1 E0 m1 ->
bind_parameters e m1 params vl m2 ->
bind_parameters e m ((id, ty) :: params) (v1 :: vl) m2.
(** Return the list of blocks in the codomain of [e], with low and high bounds. *)
Definition block_of_binding (id_b_ty: ident * (block * type)) :=
match id_b_ty with (id, (b, ty)) => (b, 0, sizeof ge ty) end.
Definition blocks_of_env (e: env) : list (block * Z * Z) :=
List.map block_of_binding (PTree.elements e).
(** Selection of the appropriate case of a [switch], given the value [n] of the selector expression. *)
Fixpoint select_switch_default (sl: labeled_statements): labeled_statements :=
match sl with
| LSnil => sl
| LScons None s sl' => sl
| LScons (Some i) s sl' => select_switch_default sl'
end.
Fixpoint select_switch_case (n: Z) (sl: labeled_statements): option labeled_statements :=
match sl with
| LSnil => None
| LScons None s sl' => select_switch_case n sl'
| LScons (Some c) s sl' => if zeq c n then Some sl else select_switch_case n sl'
end.
Definition select_switch (n: Z) (sl: labeled_statements): labeled_statements :=
match select_switch_case n sl with
| Some sl' => sl'
| None => select_switch_default sl
end.
(** Turn a labeled statement into a sequence *)
Fixpoint seq_of_labeled_statement (sl: labeled_statements) : statement :=
match sl with
| LSnil => Sskip
| LScons _ s sl' => Ssequence s (seq_of_labeled_statement sl')
end.
(** Extract the values from a list of function arguments *)
Inductive cast_arguments (m: mem): exprlist -> typelist -> list val -> Prop :=
| cast_args_nil:
cast_arguments m Enil Tnil nil
| cast_args_cons: forall v ty el targ1 targs v1 vl,
sem_cast v ty targ1 m = Some v1 -> cast_arguments m el targs vl ->
cast_arguments m (Econs (Eval v ty) el) (Tcons targ1 targs) (v1 :: vl).
(** ** Reduction semantics for expressions *)
Section EXPR.
Variable e: env.
(** The semantics of expressions follows the popular Wright-Felleisen style. It is a small-step semantics that reduces one redex at a time. We first define head reductions (at the top of an expression, then use reduction contexts to define reduction within an expression. *)
(** Head reduction for l-values. *)
Inductive lred: expr -> mem -> expr -> mem -> Prop :=
| red_var_local: forall x ty m b,
e!x = Some(b, ty) ->
lred (Evar x ty) m
(Eloc b Ptrofs.zero ty) m
| red_var_global: forall x ty m b,
e!x = None ->
Genv.find_symbol ge x = Some b ->
lred (Evar x ty) m
(Eloc b Ptrofs.zero ty) m
| red_deref: forall b ofs ty1 ty m,
lred (Ederef (Eval (Vptr b ofs) ty1) ty) m
(Eloc b ofs ty) m
| red_field_struct: forall b ofs id co a f ty m delta,
ge.(genv_cenv)!id = Some co ->
field_offset ge f (co_members co) = OK delta ->
lred (Efield (Eval (Vptr b ofs) (Tstruct id a)) f ty) m
(Eloc b (Ptrofs.add ofs (Ptrofs.repr delta)) ty) m
| red_field_union: forall b ofs id co a f ty m,
ge.(genv_cenv)!id = Some co ->
lred (Efield (Eval (Vptr b ofs) (Tunion id a)) f ty) m
(Eloc b ofs ty) m.
(** Head reductions for r-values *)
Inductive rred: expr -> mem -> trace -> expr -> mem -> Prop :=
| red_rvalof: forall b ofs ty m t v,
deref_loc ty m b ofs t v ->
rred (Evalof (Eloc b ofs ty) ty) m
t (Eval v ty) m
| red_addrof: forall b ofs ty1 ty m,
rred (Eaddrof (Eloc b ofs ty1) ty) m
E0 (Eval (Vptr b ofs) ty) m
| red_unop: forall op v1 ty1 ty m v,
sem_unary_operation op v1 ty1 m = Some v ->
rred (Eunop op (Eval v1 ty1) ty) m
E0 (Eval v ty) m
| red_binop: forall op v1 ty1 v2 ty2 ty m v,
sem_binary_operation ge op v1 ty1 v2 ty2 m = Some v ->
rred (Ebinop op (Eval v1 ty1) (Eval v2 ty2) ty) m
E0 (Eval v ty) m
| red_cast: forall ty v1 ty1 m v,
sem_cast v1 ty1 ty m = Some v ->
rred (Ecast (Eval v1 ty1) ty) m
E0 (Eval v ty) m
| red_seqand_true: forall v1 ty1 r2 ty m,
bool_val v1 ty1 m = Some true ->
rred (Eseqand (Eval v1 ty1) r2 ty) m
E0 (Eparen r2 type_bool ty) m
| red_seqand_false: forall v1 ty1 r2 ty m,
bool_val v1 ty1 m = Some false ->
rred (Eseqand (Eval v1 ty1) r2 ty) m
E0 (Eval (Vint Int.zero) ty) m
| red_seqor_true: forall v1 ty1 r2 ty m,
bool_val v1 ty1 m = Some true ->
rred (Eseqor (Eval v1 ty1) r2 ty) m
E0 (Eval (Vint Int.one) ty) m
| red_seqor_false: forall v1 ty1 r2 ty m,
bool_val v1 ty1 m = Some false ->
rred (Eseqor (Eval v1 ty1) r2 ty) m
E0 (Eparen r2 type_bool ty) m
| red_condition: forall v1 ty1 r1 r2 ty b m,
bool_val v1 ty1 m = Some b ->
rred (Econdition (Eval v1 ty1) r1 r2 ty) m
E0 (Eparen (if b then r1 else r2) ty ty) m
| red_sizeof: forall ty1 ty m,
rred (Esizeof ty1 ty) m
E0 (Eval (Vptrofs (Ptrofs.repr (sizeof ge ty1))) ty) m
| red_alignof: forall ty1 ty m,
rred (Ealignof ty1 ty) m
E0 (Eval (Vptrofs (Ptrofs.repr (alignof ge ty1))) ty) m
| red_assign: forall b ofs ty1 v2 ty2 m v t m',
sem_cast v2 ty2 ty1 m = Some v ->
assign_loc ty1 m b ofs v t m' ->
rred (Eassign (Eloc b ofs ty1) (Eval v2 ty2) ty1) m
t (Eval v ty1) m'
| red_assignop: forall op b ofs ty1 v2 ty2 tyres m t v1,
deref_loc ty1 m b ofs t v1 ->
rred (Eassignop op (Eloc b ofs ty1) (Eval v2 ty2) tyres ty1) m
t (Eassign (Eloc b ofs ty1)
(Ebinop op (Eval v1 ty1) (Eval v2 ty2) tyres) ty1) m
| red_postincr: forall id b ofs ty m t v1 op,
deref_loc ty m b ofs t v1 ->
op = match id with Incr => Oadd | Decr => Osub end ->
rred (Epostincr id (Eloc b ofs ty) ty) m
t (Ecomma (Eassign (Eloc b ofs ty)
(Ebinop op (Eval v1 ty)
(Eval (Vint Int.one) type_int32s)
(incrdecr_type ty))
ty)
(Eval v1 ty) ty) m
| red_comma: forall v ty1 r2 ty m,
typeof r2 = ty ->
rred (Ecomma (Eval v ty1) r2 ty) m
E0 r2 m
| red_paren: forall v1 ty1 ty2 ty m v,
sem_cast v1 ty1 ty2 m = Some v ->
rred (Eparen (Eval v1 ty1) ty2 ty) m
E0 (Eval v ty) m
| red_builtin: forall ef tyargs el ty m vargs t vres m',
cast_arguments m el tyargs vargs ->
external_call ef ge vargs m t vres m' ->
rred (Ebuiltin ef tyargs el ty) m
t (Eval vres ty) m'.
(** Head reduction for function calls. (More exactly, identification of function calls that can reduce.) *)
Inductive callred: expr -> mem -> fundef -> list val -> type -> Prop :=
| red_call: forall vf tyf m tyargs tyres cconv el ty fd vargs,
Genv.find_funct ge vf = Some fd ->
cast_arguments m el tyargs vargs ->
type_of_fundef fd = Tfunction tyargs tyres cconv ->
classify_fun tyf = fun_case_f tyargs tyres cconv ->
callred (Ecall (Eval vf tyf) el ty) m
fd vargs ty.
(** Reduction contexts.  In accordance with C's nondeterministic semantics, we allow reduction both to the left and to the right of a binary operator. To enforce C's notion of sequence point, reductions within a conditional [a ? b : c] can only take place in [a], not in [b] nor [c]; reductions within a sequential "or" / "and" [a && b] or [a || b] can only take place in [a], not in [b]; and reductions within a sequence [a, b] can only take place in [a], not in [b].  Reduction contexts are represented by functions [C] from expressions to expressions, suitably constrained by the [context from to C] predicate below.  Contexts are "kinded" with respect to l-values and r-values: [from] is the kind of the hole in the context and [to] is the kind of the term resulting from filling the hole. *)
Inductive kind : Type := LV | RV.
Inductive context: kind -> kind -> (expr -> expr) -> Prop :=
| ctx_top: forall k,
context k k (fun x => x)
| ctx_deref: forall k C ty,
context k RV C -> context k LV (fun x => Ederef (C x) ty)
| ctx_field: forall k C f ty,
context k RV C -> context k LV (fun x => Efield (C x) f ty)
| ctx_rvalof: forall k C ty,
context k LV C -> context k RV (fun x => Evalof (C x) ty)
| ctx_addrof: forall k C ty,
context k LV C -> context k RV (fun x => Eaddrof (C x) ty)
| ctx_unop: forall k C op ty,
context k RV C -> context k RV (fun x => Eunop op (C x) ty)
| ctx_binop_left: forall k C op e2 ty,
context k RV C -> context k RV (fun x => Ebinop op (C x) e2 ty)
| ctx_binop_right: forall k C op e1 ty,
context k RV C -> context k RV (fun x => Ebinop op e1 (C x) ty)
| ctx_cast: forall k C ty,
context k RV C -> context k RV (fun x => Ecast (C x) ty)
| ctx_seqand: forall k C r2 ty,
context k RV C -> context k RV (fun x => Eseqand (C x) r2 ty)
| ctx_seqor: forall k C r2 ty,
context k RV C -> context k RV (fun x => Eseqor (C x) r2 ty)
| ctx_condition: forall k C r2 r3 ty,
context k RV C -> context k RV (fun x => Econdition (C x) r2 r3 ty)
| ctx_assign_left: forall k C e2 ty,
context k LV C -> context k RV (fun x => Eassign (C x) e2 ty)
| ctx_assign_right: forall k C e1 ty,
context k RV C -> context k RV (fun x => Eassign e1 (C x) ty)
| ctx_assignop_left: forall k C op e2 tyres ty,
context k LV C -> context k RV (fun x => Eassignop op (C x) e2 tyres ty)
| ctx_assignop_right: forall k C op e1 tyres ty,
context k RV C -> context k RV (fun x => Eassignop op e1 (C x) tyres ty)
| ctx_postincr: forall k C id ty,
context k LV C -> context k RV (fun x => Epostincr id (C x) ty)
| ctx_call_left: forall k C el ty,
context k RV C -> context k RV (fun x => Ecall (C x) el ty)
| ctx_call_right: forall k C e1 ty,
contextlist k C -> context k RV (fun x => Ecall e1 (C x) ty)
| ctx_builtin: forall k C ef tyargs ty,
contextlist k C -> context k RV (fun x => Ebuiltin ef tyargs (C x) ty)
| ctx_comma: forall k C e2 ty,
context k RV C -> context k RV (fun x => Ecomma (C x) e2 ty)
| ctx_paren: forall k C tycast ty,
context k RV C -> context k RV (fun x => Eparen (C x) tycast ty)
with contextlist: kind -> (expr -> exprlist) -> Prop :=
| ctx_list_head: forall k C el,
context k RV C -> contextlist k (fun x => Econs (C x) el)
| ctx_list_tail: forall k C e1,
contextlist k C -> contextlist k (fun x => Econs e1 (C x)).
(** In a nondeterministic semantics, expressions can go wrong according to one reduction order while being defined according to another. Consider for instance [(x = 1) + (10 / x)] where [x] is initially [0]. This expression goes wrong if evaluated right-to-left, but is defined if evaluated left-to-right.  Since our compiler is going to pick one particular evaluation order, we must make sure that all orders are safe, i.e. never evaluate a subexpression that goes wrong.  Being safe is a stronger requirement than just not getting stuck during reductions.  Consider [f() + (10 / x)], where [f()] does not terminate. This expression is never stuck because the evaluation of [f()] can make infinitely many transitions.  Yet it contains a subexpression [10 / x] that can go wrong if [x = 0], and the compiler may choose to evaluate [10 / x] first, before calling [f()].  Therefore, we must make sure that not only an expression cannot get stuck, but none of its subexpressions can either.  We say that a subexpression is not immediately stuck if it is a value (of the appropriate kind) or it can reduce (at head or within). *)
Inductive imm_safe: kind -> expr -> mem -> Prop :=
| imm_safe_val: forall v ty m,
imm_safe RV (Eval v ty) m
| imm_safe_loc: forall b ofs ty m,
imm_safe LV (Eloc b ofs ty) m
| imm_safe_lred: forall to C e m e' m',
lred e m e' m' ->
context LV to C ->
imm_safe to (C e) m
| imm_safe_rred: forall to C e m t e' m',
rred e m t e' m' ->
context RV to C ->
imm_safe to (C e) m
| imm_safe_callred: forall to C e m fd args ty,
callred e m fd args ty ->
context RV to C ->
imm_safe to (C e) m.
Definition not_stuck (e: expr) (m: mem) : Prop :=
forall k C e' ,
context k RV C -> e = C e' -> imm_safe k e' m.
End EXPR.
(** ** Transition semantics. *)
(** Continuations describe the computations that remain to be performed after the statement or expression under consideration has evaluated completely. *)
Inductive cont: Type :=
| Kstop: cont
| Kdo: cont -> cont       (**r [Kdo k] = after [x] in [x;] *)
| Kseq: statement -> cont -> cont    (**r [Kseq s2 k] = after [s1] in [s1;s2] *)
| Kifthenelse: statement -> statement -> cont -> cont     (**r [Kifthenelse s1 s2 k] = after [x] in [if (x) { s1 } else { s2 }] *)
| Kwhile1: expr -> statement -> cont -> cont      (**r [Kwhile1 x s k] = after [x] in [while(x) s] *)
| Kwhile2: expr -> statement -> cont -> cont      (**r [Kwhile x s k] = after [s] in [while (x) s] *)
| Kdowhile1: expr -> statement -> cont -> cont    (**r [Kdowhile1 x s k] = after [s] in [do s while (x)] *)
| Kdowhile2: expr -> statement -> cont -> cont    (**r [Kdowhile2 x s k] = after [x] in [do s while (x)] *)
| Kfor2: expr -> statement -> statement -> cont -> cont   (**r [Kfor2 e2 e3 s k] = after [e2] in [for(e1;e2;e3) s] *)
| Kfor3: expr -> statement -> statement -> cont -> cont   (**r [Kfor3 e2 e3 s k] = after [s] in [for(e1;e2;e3) s] *)
| Kfor4: expr -> statement -> statement -> cont -> cont   (**r [Kfor4 e2 e3 s k] = after [e3] in [for(e1;e2;e3) s] *)
| Kswitch1: labeled_statements -> cont -> cont     (**r [Kswitch1 ls k] = after [e] in [switch(e) { ls }] *)
| Kswitch2: cont -> cont       (**r catches [break] statements arising out of [switch] *)
| Kreturn: cont -> cont        (**r [Kreturn k] = after [e] in [return e;] *)
| Kcall: function ->           (**r calling function *)
env ->                (**r local env of calling function *)
(expr -> expr) ->     (**r context of the call *)
type ->               (**r type of call expression *)
cont -> cont.
(** Pop continuation until a call or stop *)
Fixpoint call_cont (k: cont) : cont :=
match k with
| Kstop => k
| Kdo k => k
| Kseq s k => call_cont k
| Kifthenelse s1 s2 k => call_cont k
| Kwhile1 e s k => call_cont k
| Kwhile2 e s k => call_cont k
| Kdowhile1 e s k => call_cont k
| Kdowhile2 e s k => call_cont k
| Kfor2 e2 e3 s k => call_cont k
| Kfor3 e2 e3 s k => call_cont k
| Kfor4 e2 e3 s k => call_cont k
| Kswitch1 ls k => call_cont k
| Kswitch2 k => call_cont k
| Kreturn k => call_cont k
| Kcall _ _ _ _ _ => k
end.
Definition is_call_cont (k: cont) : Prop :=
match k with
| Kstop => True
| Kcall _ _ _ _ _ => True
| _ => False
end.
(** Execution states of the program are grouped in 4 classes corresponding to the part of the program we are currently executing.  It can be a statement ([State]), an expression ([ExprState]), a transition from a calling function to a called function ([Callstate]), or the symmetrical transition from a function back to its caller ([Returnstate]). *)
Inductive state: Type :=
| State                               (**r execution of a statement *)
(f: function)
(s: statement)
(k: cont)
(e: env)
(m: mem) : state
| ExprState                           (**r reduction of an expression *)
(f: function)
(r: expr)
(k: cont)
(e: env)
(m: mem) : state
| Callstate                           (**r calling a function *)
(fd: fundef)
(args: list val)
(k: cont)
(m: mem) : state
| Returnstate                         (**r returning from a function *)
(res: val)
(k: cont)
(m: mem) : state
| Stuckstate.                         (**r undefined behavior occurred *)
(** 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
| Swhile a s1 =>
find_label lbl s1 (Kwhile2 a s1 k)
| Sdowhile a s1 =>
find_label lbl s1 (Kdowhile1 a s1 k)
| Sfor a1 a2 a3 s1 =>
match find_label lbl a1 (Kseq (Sfor Sskip a2 a3 s1) k) with
| Some sk => Some sk
| None =>
match find_label lbl s1 (Kfor3 a2 a3 s1 k) with
| Some sk => Some sk
| None => find_label lbl a3 (Kfor4 a2 a3 s1 k)
end
end
| Sswitch e sl =>
find_label_ls lbl sl (Kswitch2 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
| LSnil => None
| LScons _ 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.
(** We separate the transition rules in two groups: - one group that deals with reductions over expressions; - the other group that deals with everything else: statements, function calls, etc.  This makes it easy to express different reduction strategies for expressions: the second group of rules can be reused as is. *)
Inductive estep: state -> trace -> state -> Prop :=
| step_lred: forall C f a k e m a' m',
lred e a m a' m' ->
context LV RV C ->
estep (ExprState f (C a) k e m)
E0 (ExprState f (C a') k e m')
| step_rred: forall C f a k e m t a' m',
rred a m t a' m' ->
context RV RV C ->
estep (ExprState f (C a) k e m)
t (ExprState f (C a') k e m')
| step_call: forall C f a k e m fd vargs ty,
callred a m fd vargs ty ->
context RV RV C ->
estep (ExprState f (C a) k e m)
E0 (Callstate fd vargs (Kcall f e C ty k) m)
| step_stuck: forall C f a k e m K,
context K RV C -> ~(imm_safe e K a m) ->
estep (ExprState f (C a) k e m)
E0 Stuckstate.
Inductive sstep: state -> trace -> state -> Prop :=
| step_do_1: forall f x k e m,
sstep (State f (Sdo x) k e m)
E0 (ExprState f x (Kdo k) e m)
| step_do_2: forall f v ty k e m,
sstep (ExprState f (Eval v ty) (Kdo k) e m)
E0 (State f Sskip k e m)
| step_seq:  forall f s1 s2 k e m,
sstep (State f (Ssequence s1 s2) k e m)
E0 (State f s1 (Kseq s2 k) e m)
| step_skip_seq: forall f s k e m,
sstep (State f Sskip (Kseq s k) e m)
E0 (State f s k e m)
| step_continue_seq: forall f s k e m,
sstep (State f Scontinue (Kseq s k) e m)
E0 (State f Scontinue k e m)
| step_break_seq: forall f s k e m,
sstep (State f Sbreak (Kseq s k) e m)
E0 (State f Sbreak k e m)
| step_ifthenelse_1: forall f a s1 s2 k e m,
sstep (State f (Sifthenelse a s1 s2) k e m)
E0 (ExprState f a (Kifthenelse s1 s2 k) e m)
| step_ifthenelse_2:  forall f v ty s1 s2 k e m b,
bool_val v ty m = Some b ->
sstep (ExprState f (Eval v ty) (Kifthenelse s1 s2 k) e m)
E0 (State f (if b then s1 else s2) k e m)
| step_while: forall f x s k e m,
sstep (State f (Swhile x s) k e m)
E0 (ExprState f x (Kwhile1 x s k) e m)
| step_while_false: forall f v ty x s k e m,
bool_val v ty m = Some false ->
sstep (ExprState f (Eval v ty) (Kwhile1 x s k) e m)
E0 (State f Sskip k e m)
| step_while_true: forall f v ty x s k e m ,
bool_val v ty m = Some true ->
sstep (ExprState f (Eval v ty) (Kwhile1 x s k) e m)
E0 (State f s (Kwhile2 x s k) e m)
| step_skip_or_continue_while: forall f s0 x s k e m,
s0 = Sskip \/ s0 = Scontinue ->
sstep (State f s0 (Kwhile2 x s k) e m)
E0 (State f (Swhile x s) k e m)
| step_break_while: forall f x s k e m,
sstep (State f Sbreak (Kwhile2 x s k) e m)
E0 (State f Sskip k e m)
| step_dowhile: forall f a s k e m,
sstep (State f (Sdowhile a s) k e m)
E0 (State f s (Kdowhile1 a s k) e m)
| step_skip_or_continue_dowhile: forall f s0 x s k e m,
s0 = Sskip \/ s0 = Scontinue ->
sstep (State f s0 (Kdowhile1 x s k) e m)
E0 (ExprState f x (Kdowhile2 x s k) e m)
| step_dowhile_false: forall f v ty x s k e m,
bool_val v ty m = Some false ->
sstep (ExprState f (Eval v ty) (Kdowhile2 x s k) e m)
E0 (State f Sskip k e m)
| step_dowhile_true: forall f v ty x s k e m,
bool_val v ty m = Some true ->
sstep (ExprState f (Eval v ty) (Kdowhile2 x s k) e m)
E0 (State f (Sdowhile x s) k e m)
| step_break_dowhile: forall f a s k e m,
sstep (State f Sbreak (Kdowhile1 a s k) e m)
E0 (State f Sskip k e m)
| step_for_start: forall f a1 a2 a3 s k e m,
a1 <> Sskip ->
sstep (State f (Sfor a1 a2 a3 s) k e m)
E0 (State f a1 (Kseq (Sfor Sskip a2 a3 s) k) e m)
| step_for: forall f a2 a3 s k e m,
sstep (State f (Sfor Sskip a2 a3 s) k e m)
E0 (ExprState f a2 (Kfor2 a2 a3 s k) e m)
| step_for_false: forall f v ty a2 a3 s k e m,
bool_val v ty m = Some false ->
sstep (ExprState f (Eval v ty) (Kfor2 a2 a3 s k) e m)
E0 (State f Sskip k e m)
| step_for_true: forall f v ty a2 a3 s k e m,
bool_val v ty m = Some true ->
sstep (ExprState f (Eval v ty) (Kfor2 a2 a3 s k) e m)
E0 (State f s (Kfor3 a2 a3 s k) e m)
| step_skip_or_continue_for3: forall f x a2 a3 s k e m,
x = Sskip \/ x = Scontinue ->
sstep (State f x (Kfor3 a2 a3 s k) e m)
E0 (State f a3 (Kfor4 a2 a3 s k) e m)
| step_break_for3: forall f a2 a3 s k e m,
sstep (State f Sbreak (Kfor3 a2 a3 s k) e m)
E0 (State f Sskip k e m)
| step_skip_for4: forall f a2 a3 s k e m,
sstep (State f Sskip (Kfor4 a2 a3 s k) e m)
E0 (State f (Sfor Sskip a2 a3 s) k e m)
| step_return_0: forall f k e m m',
Mem.free_list m (blocks_of_env e) = Some m' ->
sstep (State f (Sreturn None) k e m)
E0 (Returnstate Vundef (call_cont k) m')
| step_return_1: forall f x k e m,
sstep (State f (Sreturn (Some x)) k e m)
E0 (ExprState f x (Kreturn k) e  m)
| step_return_2:  forall f v1 ty k e m v2 m',
sem_cast v1 ty f.(fn_return) m = Some v2 ->
Mem.free_list m (blocks_of_env e) = Some m' ->
sstep (ExprState f (Eval v1 ty) (Kreturn k) e m)
E0 (Returnstate v2 (call_cont k) m')
| step_skip_call: forall f k e m m',
is_call_cont k ->
Mem.free_list m (blocks_of_env e) = Some m' ->
sstep (State f Sskip k e m)
E0 (Returnstate Vundef k m')
| step_switch: forall f x sl k e m,
sstep (State f (Sswitch x sl) k e m)
E0 (ExprState f x (Kswitch1 sl k) e m)
| step_expr_switch: forall f ty sl k e m v n,
sem_switch_arg v ty = Some n ->
sstep (ExprState f (Eval v ty) (Kswitch1 sl k) e m)
E0 (State f (seq_of_labeled_statement (select_switch n sl)) (Kswitch2 k) e m)
| step_skip_break_switch: forall f x k e m,
x = Sskip \/ x = Sbreak ->
sstep (State f x (Kswitch2 k) e m)
E0 (State f Sskip k e m)
| step_continue_switch: forall f k e m,
sstep (State f Scontinue (Kswitch2 k) e m)
E0 (State f Scontinue k e m)
| step_label: forall f lbl s k e m,
sstep (State f (Slabel lbl s) k e m)
E0 (State f s k e m)
| step_goto: forall f lbl k e m s' k',
find_label lbl f.(fn_body) (call_cont k) = Some (s', k') ->
sstep (State f (Sgoto lbl) k e m)
E0 (State f s' k' e m)
| step_internal_function: forall f vargs k m e m1 m2,
list_norepet (var_names (fn_params f) ++ var_names (fn_vars f)) ->
alloc_variables empty_env m (f.(fn_params) ++ f.(fn_vars)) e m1 ->
bind_parameters e m1 f.(fn_params) vargs m2 ->
sstep (Callstate (Internal f) vargs k m)
E0 (State f f.(fn_body) k e m2)
| step_external_function: forall ef targs tres cc vargs k m vres t m',
external_call ef  ge vargs m t vres m' ->
sstep (Callstate (External ef targs tres cc) vargs k m)
t (Returnstate vres k m')
| step_returnstate: forall v f e C ty k m,
sstep (Returnstate v (Kcall f e C ty k) m)
E0 (ExprState f (C (Eval v ty)) k e m).
Definition step (S: state) (t: trace) (S': state) : Prop :=
estep S t S' \/ sstep S t S'.
End SEMANTICS.
(** * 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 := 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 cc_default ->
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.
(** Wrapping up these definitions in a small-step semantics. *)
Definition semantics (p: program) :=
Semantics_gen step (initial_state p) final_state (globalenv p) (globalenv p).
(** This semantics has the single-event property. *)

(* Specifications: *)
Lemma semantics_single_events:
forall p, single_events (semantics p).