[Bug c/46181] New: Feature request: "free-like" attribute

["m.j.thayer at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46181

           Summary: Feature request: "free-like" attribute
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: m.j.thayer@googlemail.com


It would be nice for purposes of static error checking to be able to mark
functions as destructors for some resource.  Specifically, that a if a value is
passed from a variable to argument n of the function then it is no longer valid
after the call to the function.  Optionally with an "invalid" value that may be
assigned to the variable afterwards.

E.g.

int close(int fd) __attribute__(( free(1, -1) ));  /* Says that the value
passed to the first argument is invalid hereafter, and that the variable it
came from can be marked invalid by setting it to -1 */

So that the compiler can see that the following is bad:

int fd = open("filename", O_CREAT);
...
if (close(fd) < 0) { ... }
do_something_with(fd);

but the following might be alright:

int fd = open("filename", O_CREAT);
...
if (close(fd) < 0) { ... }
fd = -1;
do_something_with(fd);

It might also make sense to be able to tag a typedef as a resource type with
information about a free-like function and an invalid value:

typedef int myfile __attribute(( resource(close, -1) ));