The first step in adding a new GIMPLE statement code, is
modifying the file gimple.def, which contains all the GIMPLE
codes. Then you must add a corresponding gimple_statement_base subclass
located in gimple.h. This in turn, will require you to add a
corresponding GTY tag in gsstruct.def, and code to handle
this tag in gss_for_code which is located in gimple.c.
In order for the garbage collector to know the size of the
structure you created in gimple.h, you need to add a case to
handle your new GIMPLE statement in gimple_size which is located
in gimple.c.
You will probably want to create a function to build the new
gimple statement in gimple.c. The function should be called
gimple_build_new-tuple-name, and should return the new tuple
as a pointer to the appropriate gimple_statement_base subclass.
If your new statement requires accessors for any members or
operands it may have, put simple inline accessors in
gimple.h and any non-trivial accessors in gimple.c with a
corresponding prototype in gimple.h.
You should add the new statement subclass to the class hierarchy diagram
in gimple.texi.