Adding a new DECL tree consists of the following steps
DECL nodeDECL nodes, there is a .def file
in each frontend directory where the tree code should be added.
For DECL nodes that are part of the middle-end, the code should
be added to tree.def.
DECL node struct tree_foo_decl
{
struct tree_decl_with_vis common;
}
Would create a structure name tree_foo_decl that inherits from
struct tree_decl_with_vis.
For language specific DECL nodes, this new structure type
should go in the appropriate .h file.
For DECL nodes that are part of the middle-end, the structure
type should go in tree.h.
DECL
node structure type is required to have a unique enumerator value
specified with it.
For language specific DECL nodes, this new enumerator value
should go in the appropriate .def file.
For DECL nodes that are part of the middle-end, the enumerator
values are specified in treestruct.def.
union tree_nodeunion tree_node.
For language specific DECL nodes, a new entry should be added
to the appropriate .h file of the form
struct tree_foo_decl GTY ((tag ("TS_VAR_DECL"))) foo_decl;
For DECL nodes that are part of the middle-end, the additional
member goes directly into union tree_node in tree.h.
union tree_node is legal, and whether a certain DECL node
contains one of the enumerated DECL node structures in the
hierarchy, a simple lookup table is used.
This lookup table needs to be kept up to date with the tree structure
hierarchy, or else checking and containment macros will fail
inappropriately.
For language specific DECL nodes, their is an init_ts
function in an appropriate .c file, which initializes the lookup
table.
Code setting up the table for new DECL nodes should be added
there.
For each DECL tree code and enumerator value representing a
member of the inheritance hierarchy, the table should contain 1 if
that tree code inherits (directly or indirectly) from that member.
Thus, a FOO_DECL node derived from struct decl_with_rtl,
and enumerator value TS_FOO_DECL, would be set up as follows
tree_contains_struct[FOO_DECL][TS_FOO_DECL] = 1;
tree_contains_struct[FOO_DECL][TS_DECL_WRTL] = 1;
tree_contains_struct[FOO_DECL][TS_DECL_COMMON] = 1;
tree_contains_struct[FOO_DECL][TS_DECL_MINIMAL] = 1;
For DECL nodes that are part of the middle-end, the setup code
goes into tree.c.
DECL nodes access the field.
These macros generally take the following form
#define FOO_DECL_FIELDNAME(NODE) FOO_DECL_CHECK(NODE)->foo_decl.fieldname
However, if the structure is simply a base class for further structures, something like the following should be used
#define BASE_STRUCT_CHECK(T) CONTAINS_STRUCT_CHECK(T, TS_BASE_STRUCT)
#define BASE_STRUCT_FIELDNAME(NODE) \
(BASE_STRUCT_CHECK(NODE)->base_struct.fieldname