Procedure symbol tables represent the top-level scopes within procedures
and are associated with the tree_proc objects at the roots of the
abstract syntax trees for the procedures. See section Procedure Nodes.
Because the procedure symbol tables provide a superset of the block
symbol table functions, they are implemented by deriving the
proc_symtab class from the block_symtab class. Thus, all
of the block_symtab methods can also be applied to
proc_symtab objects.
Besides the inherited methods, the procedure symbol tables have some
added features. Each procedure symbol table contains a list of the
formal parameters for the procedure. The params method returns a
pointer to this list. The entries on this list must be pointers to
symbols for variables that are contained within the procedure symbol
table. (Formal parameters cannot be global variables or local variables
in inner scopes.) The symbols are listed in order. If the function
type for the procedure specifies the parameter types, they should match
the types of the variables on the parameter list.
The procedure symbol table also records the next instruction ID number
for the procedure (see section ID Numbers for Tree Nodes and Instructions). The number_locals method
handles the task of assigning ID numbers to the symbols and types in
symbol tables within the procedure (see section Numbering Types and Symbols).