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***********
Type System
***********
struct symbol is used to represent symbols & types but
most parts pertaining to the types are in the field 'ctype'.
For the purpose of this document, things can be simplified into:
.. code-block:: c
struct symbol {
enum type type; // SYM_...
struct ctype {
struct symbol *base_type;
unsigned long modifiers;
unsigned long alignment;
struct context_list *contexts;
struct indent *as;
};
};
Some bits, also related to the type, are in struct symbol itself:
* type
* size_bits
* rank
* variadic
* string
* designated_init
* forced_arg
* accessed
* transparent_union
* ``base_type`` is used for the associated base type.
* ``modifiers`` is a bit mask for type specifiers (MOD_UNSIGNED, ...),
type qualifiers (MOD_CONST, MOD_VOLATILE),
storage classes (MOD_STATIC, MOD_EXTERN, ...), as well for various
attributes. It's also used internally to keep track of some states
(MOD_ACCESS or MOD_ADDRESSABLE).
* ``alignment`` is used for the alignment, in bytes.
* ``contexts`` is used to store the informations associated with the
attribute ``context()``.
* ``as`` is used to hold the identifier of the attribute ``address_space()``.
Kind of types
=============
SYM_BASETYPE
------------
Used by integer, floating-point, void, 'type', 'incomplete' & bad types.
For integer types:
* .ctype.base_type points to ``int_ctype``, the generic/abstract integer type
* .ctype.modifiers has MOD_UNSIGNED/SIGNED/EXPLICITLY_SIGNED set accordingly.
For floating-point types:
* .ctype.base_type points to ``fp_ctype``, the generic/abstract float type
* .ctype.modifiers is zero.
For the other base types:
* .ctype.base_type is NULL
* .ctype.modifiers is zero.
SYM_NODE
--------
It's used to make variants of existing types. For example,
it's used as a top node for all declarations which can then
have their own modifiers, address_space, contexts or alignment
as well as the declaration's identifier.
Usage:
* .ctype.base_type points to the unmodified type (which must not
be a SYM_NODE itself)
* .ctype.modifiers, .as, .alignment, .contexts will contains
the 'variation' (MOD_CONST, the attributes, ...).
SYM_PTR
-------
For pointers:
* .ctype.base_type points to the pointee type
* .ctype.modifiers & .as are about the pointee too!
SYM_FN
------
For functions:
* .ctype.base_type points to the return type
* .ctype.modifiers & .as should be about the function itself
but some return type's modifiers creep here (for example, in
int foo(void), MOD_SIGNED will be set for the function).
SYM_ARRAY
---------
For arrays:
* .ctype.base_type points to the underlying type
* .ctype.modifiers & .as are a copy of the parent type (and unused)?
* for literal strings, the modifier also contains MOD_STATIC
* sym->array_size is *expression* for the array size.
SYM_STRUCT
----------
For structs:
* .ctype.base_type is NULL
* .ctype.modifiers & .as are not used?
* .ident is the name tag.
SYM_UNION
---------
Same as for structs.
SYM_ENUM
--------
For enums:
* .ctype.base_type points to the underlying type (integer)
* .ctype.modifiers contains the enum signedness
* .ident is the name tag.
SYM_BITFIELD
------------
For bitfields:
* .ctype.base_type points to the underlying type (integer)
* .ctype.modifiers & .as are a copy of the parent type (and unused)?
* .bit_size is the size of the bitfield.
SYM_RESTRICT
------------
Used for bitwise types (aka 'restricted' types):
* .ctype.base_type points to the underlying type (integer)
* .ctype.modifiers & .as are like for SYM_NODE and the modifiers
are inherited from the base type with MOD_SPECIFIER removed
* .ident is the typedef name (if any).
SYM_FOULED
----------
Used for bitwise types when the negation op (~) is
used and the bit_size is smaller than an ``int``.
There is a 1-to-1 mapping between a fouled type and
its parent bitwise type.
Usage:
* .ctype.base_type points to the parent type
* .ctype.modifiers & .as are the same as for the parent type
* .bit_size is bits_in_int.
SYM_TYPEOF
----------
Should not be present after evaluation:
* .initializer points to the expression representing the type
* .ctype is not used.
Typeofs with a type as argument are directly evaluated during parsing.
SYM_LABEL
---------
Used for labels only.
SYM_KEYWORD
-----------
Used for parsing only.
SYM_BAD
-------
Should not be used.
SYM_UNINTIALIZED
----------------
Should not be used.
|
