G++ internals - Macros

Macros

This section describes some of the macros used on trees. The list should be alphabetical. Eventually all macros should be documented here. There are some postscript drawings that can be used to better understand from of the more complex data structures, contact Mike Stump (mrs@cygnus.com ) for information about them.

BINFO_BASETYPES

A vector of additional binfos for the types inherited by this basetype. The binfos are fully unshared (except for virtual bases, in which case the binfo structure is shared).

If this basetype describes type D as inherited in C, and if the basetypes of D are E anf F, then this vector contains binfos for inheritance of E and F by C.

Has values of:

TREE_VECs

BINFO_INHERITANCE_CHAIN

Temporarily used to represent specific inheritances. It usually points to the binfo associated with the lesser derived type, but it can be reversed by reverse_path. For example:

		Z ZbY	least derived
		|
		Y YbX
		|
		X Xb	most derived
	
	TYPE_BINFO (X) == Xb
	BINFO_INHERITANCE_CHAIN (Xb) == YbX
	BINFO_INHERITANCE_CHAIN (Yb) == ZbY
	BINFO_INHERITANCE_CHAIN (Zb) == 0

Not sure is the above is really true, get_base_distance has is point towards the most derived type, opposite from above.

Set by build_vbase_path, recursive_bounded_basetype_p, get_base_distance, lookup_field, lookup_fnfields, and reverse_path.

What things can this be used on:

TREE_VECs that are binfos

BINFO_OFFSET

The offset where this basetype appears in its containing type. BINFO_OFFSET slot holds the offset (in bytes) from the base of the complete object to the base of the part of the object that is allocated on behalf of this `type'. This is always 0 except when there is multiple inheritance.

Used on TREE_VEC_ELTs of the binfos BINFO_BASETYPES (...) for example.

BINFO_VIRTUALS

A unique list of functions for the virtual function table. See also TYPE_BINFO_VIRTUALS.

What things can this be used on:

TREE_VECs that are binfos

BINFO_VTABLE

Used to find the VAR_DECL that is the virtual function table associated with this binfo. See also TYPE_BINFO_VTABLE. To get the virtual function table pointer, see CLASSTYPE_VFIELD.

What things can this be used on:

TREE_VECs that are binfos

Has values of:

VAR_DECLs that are virtual function tables

BLOCK_SUPERCONTEXT

In the outermost scope of each function, it points to the FUNCTION_DECL node. It aids in better DWARF support of inline functions.

CLASSTYPE_TAGS

CLASSTYPE_TAGS is a linked (via TREE_CHAIN) list of member classes of a class. TREE_PURPOSE is the name, TREE_VALUE is the type (pushclass scans these and calls pushtag on them.)

finish_struct scans these to produce TYPE_DECLs to add to the TYPE_FIELDS of the type.

It is expected that name found in the TREE_PURPOSE slot is unique, resolve_scope_to_name is one such place that depends upon this uniqueness.

CLASSTYPE_METHOD_VEC

The following is true after finish_struct has been called (on the class?) but not before. Before finish_struct is called, things are different to some extent. Contains a TREE_VEC of methods of the class. The TREE_VEC_LENGTH is the number of differently named methods plus one for the 0th entry. The 0th entry is always allocated, and reserved for ctors and dtors. If there are none, TREE_VEC_ELT(N,0) == NULL_TREE. Each entry of the TREE_VEC is a FUNCTION_DECL. For each FUNCTION_DECL, there is a DECL_CHAIN slot. If the FUNCTION_DECL is the last one with a given name, the DECL_CHAIN slot is NULL_TREE. Otherwise it is the next method that has the same name (but a different signature). It would seem that it is not true that because the DECL_CHAIN slot is used in this way, we cannot call pushdecl to put the method in the global scope (cause that would overwrite the TREE_CHAIN slot), because they use different _CHAINs. finish_struct_methods setups up one version of the TREE_CHAIN slots on the FUNCTION_DECLs.

friends are kept in TREE_LISTs, so that there's no need to use their TREE_CHAIN slot for anything.

Has values of:

TREE_VECs

CLASSTYPE_VFIELD

Seems to be in the process of being renamed TYPE_VFIELD. Use on types to get the main virtual function table pointer. To get the virtual function table use BINFO_VTABLE (TYPE_BINFO ()).

Has values of:

FIELD_DECLs that are virtual function table pointers

What things can this be used on:

RECORD_TYPEs

DECL_CLASS_CONTEXT

Identifies the context that the _DECL was found in. For virtual function tables, it points to the type associated with the virtual function table. See also DECL_CONTEXT, DECL_FIELD_CONTEXT and DECL_FCONTEXT.

The difference between this and DECL_CONTEXT, is that for virtuals functions like:

	struct A
	{
	  virtual int f ();
	};
	
	struct B : A
	{
	  int f ();
	};
	
	DECL_CONTEXT (A::f) == A
	DECL_CLASS_CONTEXT (A::f) == A
	
	DECL_CONTEXT (B::f) == A
	DECL_CLASS_CONTEXT (B::f) == B

Has values of:

RECORD_TYPEs, or UNION_TYPEs

What things can this be used on:

TYPE_DECLs, _DECLs

DECL_CONTEXT

Identifies the context that the _DECL was found in. Can be used on virtual function tables to find the type associated with the virtual function table, but since they are FIELD_DECLs, DECL_FIELD_CONTEXT is a better access method. Internally the same as DECL_FIELD_CONTEXT, so don't us both. See also DECL_FIELD_CONTEXT, DECL_FCONTEXT and DECL_CLASS_CONTEXT.

Has values of:

RECORD_TYPEs

What things can this be used on:

VAR_DECLs that are virtual function tables
_DECLs

DECL_FIELD_CONTEXT

Identifies the context that the FIELD_DECL was found in. Internally the same as DECL_CONTEXT, so don't us both. See also DECL_CONTEXT, DECL_FCONTEXT and DECL_CLASS_CONTEXT.

Has values of:

RECORD_TYPEs

What things can this be used on:

FIELD_DECLs that are virtual function pointers
FIELD_DECLs

DECL_NESTED_TYPENAME

Holds the fully qualified type name. Example, Base::Derived.

Has values of:

IDENTIFIER_NODEs

What things can this be used on:

TYPE_DECLs

DECL_NAME

Has values of:

0 for things that don't have names
IDENTIFIER_NODEs for TYPE_DECLs

DECL_IGNORED_P

A bit that can be set to inform the debug information output routines in the back-end that a certain _DECL node should be totally ignored.

Used in cases where it is known that the debugging information will be output in another file, or where a sub-type is known not to be needed because the enclosing type is not needed.

A compiler constructed virtual destructor in derived classes that do not define an explicit destructor that was defined explicit in a base class has this bit set as well. Also used on __FUNCTION__ and __PRETTY_FUNCTION__ to mark they are ``compiler generated.'' c-decl and c-lex.c both want DECL_IGNORED_P set for ``internally generated vars,'' and ``user-invisible variable.''

Functions built by the C++ front-end such as default destructors, virtual destructors and default constructors want to be marked that they are compiler generated, but unsure why.

Currently, it is used in an absolute way in the C++ front-end, as an optimization, to tell the debug information output routines to not generate debugging information that will be output by another separately compiled file.

DECL_VIRTUAL_P

A flag used on FIELD_DECLs and VAR_DECLs. (Documentation in tree.h is wrong.) Used in VAR_DECLs to indicate that the variable is a vtable. It is also used in FIELD_DECLs for vtable pointers.

What things can this be used on:

FIELD_DECLs and VAR_DECLs

DECL_VPARENT

Used to point to the parent type of the vtable if there is one, else it is just the type associated with the vtable. Because of the sharing of virtual function tables that goes on, this slot is not very useful, and is in fact, not used in the compiler at all. It can be removed.

What things can this be used on:

VAR_DECLs that are virtual function tables

Has values of:

RECORD_TYPEs maybe UNION_TYPEs

DECL_FCONTEXT

Used to find the first baseclass in which this FIELD_DECL is defined. See also DECL_CONTEXT, DECL_FIELD_CONTEXT and DECL_CLASS_CONTEXT.

How it is used:

Used when writing out debugging information about vfield and vbase decls.

What things can this be used on:

FIELD_DECLs that are virtual function pointers FIELD_DECLs

DECL_REFERENCE_SLOT

Used to hold the initialize for the reference.

What things can this be used on:

PARM_DECLs and VAR_DECLs that have a reference type

DECL_VINDEX

Used for FUNCTION_DECLs in two different ways. Before the structure containing the FUNCTION_DECL is laid out, DECL_VINDEX may point to a FUNCTION_DECL in a base class which is the FUNCTION_DECL which this FUNCTION_DECL will replace as a virtual function. When the class is laid out, this pointer is changed to an INTEGER_CST node which is suitable to find an index into the virtual function table. See get_vtable_entry as to how one can find the right index into the virtual function table. The first index 0, of a virtual function table it not used in the normal way, so the first real index is 1.

DECL_VINDEX may be a TREE_LIST, that would seem to be a list of overridden FUNCTION_DECLs. add_virtual_function has code to deal with this when it uses the variable base_fndecl_list, but it would seem that somehow, it is possible for the TREE_LIST to pursist until method_call, and it should not.

What things can this be used on:

FUNCTION_DECLs

DECL_SOURCE_FILE

Identifies what source file a particular declaration was found in.

Has values of:

"<built-in>" on TYPE_DECLs to mean the typedef is built in

DECL_SOURCE_LINE

Identifies what source line number in the source file the declaration was found at.

Has values of:

0 for an undefined label

0 for TYPE_DECLs that are internally generated

0 for FUNCTION_DECLs for functions generated by the compiler
(not yet, but should be)

0 for ``magic'' arguments to functions, that the user has no
control over

TREE_USED

Has values of:

0 for unused labels

TREE_ADDRESSABLE

A flag that is set for any type that has a constructor.

TREE_COMPLEXITY

They seem a kludge way to track recursion, poping, and pushing. They only appear in cp-decl.c and cp-decl2.c, so the are a good candidate for proper fixing, and removal.

TREE_PRIVATE

Set for FIELD_DECLs by finish_struct. But not uniformly set.

The following routines do something with PRIVATE access: build_method_call, alter_access, finish_struct_methods, finish_struct, convert_to_aggr, CWriteLanguageDecl, CWriteLanguageType, CWriteUseObject, compute_access, lookup_field, dfs_pushdecl, GNU_xref_member, dbxout_type_fields, dbxout_type_method_1

TREE_PROTECTED

The following routines do something with PROTECTED access: build_method_call, alter_access, finish_struct, convert_to_aggr, CWriteLanguageDecl, CWriteLanguageType, CWriteUseObject, compute_access, lookup_field, GNU_xref_member, dbxout_type_fields, dbxout_type_method_1

TYPE_BINFO

Used to get the binfo for the type.

Has values of:

TREE_VECs that are binfos

What things can this be used on:

RECORD_TYPEs

TYPE_BINFO_BASETYPES

See also BINFO_BASETYPES.

TYPE_BINFO_VIRTUALS

A unique list of functions for the virtual function table. See also BINFO_VIRTUALS.

What things can this be used on:

RECORD_TYPEs

TYPE_BINFO_VTABLE

Points to the virtual function table associated with the given type. See also BINFO_VTABLE.

What things can this be used on:

RECORD_TYPEs

Has values of:

VAR_DECLs that are virtual function tables

TYPE_NAME

Names the type.

Has values of:

0 for things that don't have names.
should be IDENTIFIER_NODE for RECORD_TYPEs UNION_TYPEs and
ENUM_TYPEs.
TYPE_DECL for RECORD_TYPEs, UNION_TYPEs and ENUM_TYPEs, but
shouldn't be.
TYPE_DECL for typedefs, unsure why.

What things can one use this on:

TYPE_DECLs
RECORD_TYPEs
UNION_TYPEs
ENUM_TYPEs

History:

It currently points to the TYPE_DECL for RECORD_TYPEs, UNION_TYPEs and ENUM_TYPEs, but it should be history soon.

TYPE_METHODS

Synonym for CLASSTYPE_METHOD_VEC . Chained together with TREE_CHAIN . `dbxout.c' uses this to get at the methods of a class.

TYPE_DECL

Used to represent typedefs, and used to represent bindings layers.

Components:

DECL_NAME is the name of the typedef. For example, foo would be found in the DECL_NAME slot when typedef int foo; is seen.

DECL_SOURCE_LINE identifies what source line number in the source file the declaration was found at. A value of 0 indicates that this TYPE_DECL is just an internal binding layer marker, and does not correspond to a user supplied typedef.

DECL_SOURCE_FILE

TYPE_FIELDS

A linked list (via TREE_CHAIN ) of member types of a class. The list can contain TYPE_DECL s, but there can also be other things in the list apparently. See also CLASSTYPE_TAGS .

TYPE_VIRTUAL_P

A flag used on a FIELD_DECL or a VAR_DECL , indicates it is a virtual function table or a pointer to one. When used on a FUNCTION_DECL , indicates that it is a virtual function. When used on an IDENTIFIER_NODE , indicates that a function with this same name exists and has been declared virtual.

When used on types, it indicates that the type has virtual functions, or is derived from one that does.

Not sure if the above about virtual function tables is still true. See also info on DECL_VIRTUAL_P .

What things can this be used on:

FIELD_DECLs, VAR_DECLs, FUNCTION_DECLs, IDENTIFIER_NODEs

VF_BASETYPE_VALUE

Get the associated type from the binfo that caused the given vfield to exist. This is the least derived class (the most parent class) that needed a virtual function table. It is probably the case that all uses of this field are misguided, but they need to be examined on a case-by-case basis. See history for more information on why the previous statement was made.

Set at finish_base_struct time.

What things can this be used on:

TREE_LISTs that are vfields

History:

This field was used to determine if a virtual function table's slot should be filled in with a certain virtual function, by checking to see if the type returned by VF_BASETYPE_VALUE was a parent of the context in which the old virtual function existed. This incorrectly assumes that a given type _could_ not appear as a parent twice in a given inheritance lattice. For single inheritance, this would in fact work, because a type could not possibly appear more than once in an inheritance lattice, but with multiple inheritance, a type can appear more than once.

VF_BINFO_VALUE

Identifies the binfo that caused this vfield to exist. If this vfield is from the first direct base class that has a virtual function table, then VF_BINFO_VALUE is NULL_TREE, otherwise it will be the binfo of the direct base where the vfield came from. Can use TREE_VIA_VIRTUAL on result to find out if it is a virtual base class. Related to the binfo found by

	get_binfo (VF_BASETYPE_VALUE (vfield), t, 0)

where `t' is the type that has the given vfield.

	get_binfo (VF_BASETYPE_VALUE (vfield), t, 0)

will return the binfo for the the given vfield.

May or may not be set at modify_vtable_entries time. Set at finish_base_struct time.

What things can this be used on:

TREE_LISTs that are vfields

VF_DERIVED_VALUE

Identifies the type of the most derived class of the vfield, excluding the the class this vfield is for.

Set at finish_base_struct time.

What things can this be used on:

TREE_LISTs that are vfields

VF_NORMAL_VALUE

Identifies the type of the most derived class of the vfield, including the class this vfield is for.

Set at finish_base_struct time.

What things can this be used on:

TREE_LISTs that are vfields

WRITABLE_VTABLES

This is a option that can be defined when building the compiler, that will cause the compiler to output vtables into the data segment so that the vtables maybe written. This is undefined by default, because normally the vtables should be unwritable. People that implement object I/O facilities may, or people that want to change the dynamic type of objects may want to have the vtables writable. Another way of achieving this would be to make a copy of the vtable into writable memory, but the drawback there is that that method only changes the type for one object.