(** ** Access modes *)

(** The [access_mode] function describes how a l-value of the given
type must be accessed:
- [By_value ch]: access by value, i.e. by loading from the address
  of the l-value using the memory chunk [ch];
- [By_reference]: access by reference, i.e. by just returning
  the address of the l-value (used for arrays and functions);
- [By_copy]: access is by reference, assignment is by copy
  (used for [struct] and [union] types)
- [By_nothing]: no access is possible, e.g. for the [void] type.
*)

Inductive mode: Type :=
  | By_value: memory_chunk -> mode
  | By_reference: mode
  | By_copy: mode
  | By_nothing: mode.(** ** Access modes *)

(** The [access_mode] function describes how a l-value of the given
type must be accessed:
- [By_value ch]: access by value, i.e. by loading from the address
  of the l-value using the memory chunk [ch];
- [By_reference]: access by reference, i.e. by just returning
  the address of the l-value (used for arrays and functions);
- [By_copy]: access is by reference, assignment is by copy
  (used for [struct] and [union] types)
- [By_nothing]: no access is possible, e.g. for the [void] type.
*)

Inductive mode: Type :=
  | By_value: memory_chunk -> mode
  | By_reference: mode
  | By_copy: mode
  | By_nothing: mode.(** ** Access modes *)

(** The [access_mode] function describes how a l-value of the given
type must be accessed:
- [By_value ch]: access by value, i.e. by loading from the address
  of the l-value using the memory chunk [ch];
- [By_reference]: access by reference, i.e. by just returning
  the address of the l-value (used for arrays and functions);
- [By_copy]: access is by reference, assignment is by copy
  (used for [struct] and [union] types)
- [By_nothing]: no access is possible, e.g. for the [void] type.
*)

Inductive mode: Type :=
  | By_value: memory_chunk -> mode
  | By_reference: mode
  | By_copy: mode
  | By_nothing: mode.(** ** Access modes *)

(** The [access_mode] function describes how a l-value of the given
type must be accessed:
- [By_value ch]: access by value, i.e. by loading from the address
  of the l-value using the memory chunk [ch];
- [By_reference]: access by reference, i.e. by just returning
  the address of the l-value (used for arrays and functions);
- [By_copy]: access is by reference, assignment is by copy
  (used for [struct] and [union] types)
- [By_nothing]: no access is possible, e.g. for the [void] type.
*)

Inductive mode: Type :=
  | By_value: memory_chunk -> mode
  | By_reference: mode
  | By_copy: mode
  | By_nothing: mode.(** ** Access modes *)

(** The [access_mode] function describes how a l-value of the given
type must be accessed:
- [By_value ch]: access by value, i.e. by loading from the address
  of the l-value using the memory chunk [ch];
- [By_reference]: access by reference, i.e. by just returning
  the address of the l-value (used for arrays and functions);
- [By_copy]: access is by reference, assignment is by copy
  (used for [struct] and [union] types)
- [By_nothing]: no access is possible, e.g. for the [void] type.
*)

Inductive mode: Type :=
  | By_value: memory_chunk -> mode
  | By_reference: mode
  | By_copy: mode
  | By_nothing: mode.Definition access_mode (ty: type) : mode :=
  match ty with
  | Tint I8 Signed _ => By_value Mint8signed
  | Tint I8 Unsigned _ => By_value Mint8unsigned
  | Tint I16 Signed _ => By_value Mint16signed
  | Tint I16 Unsigned _ => By_value Mint16unsigned
  | Tint I32 _ _ => By_value Mint32
  | Tint IBool _ _ => By_value Mint8unsigned
  | Tlong _ _ => By_value Mint64
  | Tfloat F32 _ => By_value Mfloat32
  | Tfloat F64 _ => By_value Mfloat64
  | Tvoid => By_nothing
  | Tpointer _ _ => By_value Mptr
  | Tarray _ _ _ => By_reference
  | Tfunction _ _ _ => By_reference
  | Tstruct _ _ => By_copy
  | Tunion _ _ => By_copy
end.(** For the purposes of the semantics and the compiler, a type denotes
  a volatile access if it carries the [volatile] attribute and it is
  accessed by value. *)

Definition type_is_volatile (ty: type) : bool :=
  match access_mode ty with
  | By_value _ => attr_volatile (attr_of_type ty)
  | _          => false
  end.

Lemma alignof_blockcopy_pos: forall env ty, alignof_blockcopy env ty > 0.