GNU Compiler Collection (GCC) Internals: Function Properties

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#### 11.8.2 Function Properties

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.

In C, the `DECL_CONTEXT` for a function maybe another function. This representation indicates that the GNU nested function extension is in use. For details on the semantics of nested functions, see the GCC Manual. The nested function can refer to local variables in its containing function. Such references are not explicitly marked in the tree structure; back ends must look at the `DECL_CONTEXT` for the referenced `VAR_DECL`. If the `DECL_CONTEXT` for the referenced `VAR_DECL` is not the same as the function currently being processed, and neither `DECL_EXTERNAL` nor `TREE_STATIC` hold, then the reference is to a local variable in a containing function, and the back end must take appropriate action.

`DECL_EXTERNAL`

  This predicate holds if the function is undefined.

`TREE_PUBLIC`

  This predicate holds if the function has external linkage.

`TREE_STATIC`

  This predicate holds if the function has been defined.

`TREE_THIS_VOLATILE`

  This predicate holds if the function does not return normally.

`TREE_READONLY`

  This predicate holds if the function can only read its arguments.

`DECL_PURE_P`

  This predicate holds if the function can only read its arguments, but may also read global memory.

`DECL_VIRTUAL_P`

  This predicate holds if the function is virtual.

`DECL_ARTIFICIAL`

  This macro holds if the function was implicitly generated by the compiler, rather than explicitly declared. In addition to implicitly generated class member functions, this macro holds for the special functions created to implement static initialization and destruction, to compute run-time type information, and so forth.

`DECL_FUNCTION_SPECIFIC_TARGET`

  This macro returns a tree node that holds the target options that are to be used to compile this particular function or `NULL_TREE` if the function is to be compiled with the target options specified on the command line.

`DECL_FUNCTION_SPECIFIC_OPTIMIZATION`

  This macro returns a tree node that holds the optimization options that are to be used to compile this particular function or `NULL_TREE` if the function is to be compiled with the optimization options specified on the command line.

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