10.10.4 Functions for C++

A function is represented by a FUNCTION_DECL node. A set of overloaded functions is sometimes represented by an OVERLOAD node.

An OVERLOAD node is not a declaration, so none of the ‘DECL_’ macros should be used on an OVERLOAD. An OVERLOAD node is similar to a TREE_LIST. Use OVL_CURRENT to get the function associated with an OVERLOAD node; use OVL_NEXT to get the next OVERLOAD node in the list of overloaded functions. The macros OVL_CURRENT and OVL_NEXT are actually polymorphic; you can use them to work with FUNCTION_DECL nodes as well as with overloads. In the case of a FUNCTION_DECL, OVL_CURRENT will always return the function itself, and OVL_NEXT will always be NULL_TREE.

To determine the scope of a function, you can use the DECL_CONTEXT macro. This macro will return the class (either a RECORD_TYPE or a UNION_TYPE) or namespace (a NAMESPACE_DECL) of which the function is a member. For a virtual function, this macro returns the class in which the function was actually defined, not the base class in which the virtual declaration occurred.

If a friend function is defined in a class scope, the DECL_FRIEND_CONTEXT macro can be used to determine the class in which it was defined. For example, in

class C { friend void f() {} };

the DECL_CONTEXT for f will be the global_namespace, but the DECL_FRIEND_CONTEXT will be the RECORD_TYPE for C.

The following macros and functions can be used on a FUNCTION_DECL:

DECL_MAIN_P

This predicate holds for a function that is the program entry point ::code.

DECL_LOCAL_FUNCTION_P

This predicate holds if the function was declared at block scope, even though it has a global scope.

DECL_ANTICIPATED

This predicate holds if the function is a built-in function but its prototype is not yet explicitly declared.

DECL_EXTERN_C_FUNCTION_P

This predicate holds if the function is declared as an ‘extern "C"’ function.

DECL_LINKONCE_P

This macro holds if multiple copies of this function may be emitted in various translation units. It is the responsibility of the linker to merge the various copies. Template instantiations are the most common example of functions for which DECL_LINKONCE_P holds; G++ instantiates needed templates in all translation units which require them, and then relies on the linker to remove duplicate instantiations.

FIXME: This macro is not yet implemented.

DECL_FUNCTION_MEMBER_P

This macro holds if the function is a member of a class, rather than a member of a namespace.

DECL_STATIC_FUNCTION_P

This predicate holds if the function a static member function.

DECL_NONSTATIC_MEMBER_FUNCTION_P

This macro holds for a non-static member function.

DECL_CONST_MEMFUNC_P

This predicate holds for a const-member function.

DECL_VOLATILE_MEMFUNC_P

This predicate holds for a volatile-member function.

DECL_CONSTRUCTOR_P

This macro holds if the function is a constructor.

DECL_NONCONVERTING_P

This predicate holds if the constructor is a non-converting constructor.

DECL_COMPLETE_CONSTRUCTOR_P

This predicate holds for a function which is a constructor for an object of a complete type.

DECL_BASE_CONSTRUCTOR_P

This predicate holds for a function which is a constructor for a base class sub-object.

DECL_COPY_CONSTRUCTOR_P

This predicate holds for a function which is a copy-constructor.

DECL_DESTRUCTOR_P

This macro holds if the function is a destructor.

DECL_COMPLETE_DESTRUCTOR_P

This predicate holds if the function is the destructor for an object a complete type.

DECL_OVERLOADED_OPERATOR_P

This macro holds if the function is an overloaded operator.

DECL_CONV_FN_P

This macro holds if the function is a type-conversion operator.

DECL_GLOBAL_CTOR_P

This predicate holds if the function is a file-scope initialization function.

DECL_GLOBAL_DTOR_P

This predicate holds if the function is a file-scope finalization function.

DECL_THUNK_P

This predicate holds if the function is a thunk.

These functions represent stub code that adjusts the this pointer and then jumps to another function. When the jumped-to function returns, control is transferred directly to the caller, without returning to the thunk. The first parameter to the thunk is always the this pointer; the thunk should add THUNK_DELTA to this value. (The THUNK_DELTA is an int, not an INTEGER_CST.)

Then, if THUNK_VCALL_OFFSET (an INTEGER_CST) is nonzero the adjusted this pointer must be adjusted again. The complete calculation is given by the following pseudo-code:

this += THUNK_DELTA
if (THUNK_VCALL_OFFSET)
  this += (*((ptrdiff_t **) this))[THUNK_VCALL_OFFSET]

Finally, the thunk should jump to the location given by DECL_INITIAL; this will always be an expression for the address of a function.

DECL_NON_THUNK_FUNCTION_P

This predicate holds if the function is not a thunk function.

GLOBAL_INIT_PRIORITY

If either DECL_GLOBAL_CTOR_P or DECL_GLOBAL_DTOR_P holds, then this gives the initialization priority for the function. The linker will arrange that all functions for which DECL_GLOBAL_CTOR_P holds are run in increasing order of priority before main is called. When the program exits, all functions for which DECL_GLOBAL_DTOR_P holds are run in the reverse order.

TYPE_RAISES_EXCEPTIONS

This macro returns the list of exceptions that a (member-)function can raise. The returned list, if non NULL, is comprised of nodes whose TREE_VALUE represents a type.

TYPE_NOTHROW_P

This predicate holds when the exception-specification of its arguments is of the form ‘()’.

DECL_ARRAY_DELETE_OPERATOR_P

This predicate holds if the function an overloaded operator delete[].