[Bug c/71152] New: NULL is not cast to (void *) as it ought to be if compiling code with -c

[rstrode at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71152

            Bug ID: 71152
           Summary: NULL is not cast to (void *) as it ought to be if
                    compiling code with -c
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rstrode at redhat dot com
  Target Milestone: ---

Created attachment 38499
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38499&action=edit
small test case try compiling with -c and without

I was refactoring code in a project and moved some code off to a helper
function.
The helper function returns an integer error code and the main function returns
a pointer.

When I moved the error handling code over from the main function to the helper
function, I neglected to change the return code from NULL to -1.

gcc didn't warn about this.

So I wrote a quick test case (attached) and discovered something very strange.

gcc does warn if you compile and link the code in one step, i.e.:

$ gcc nulltest.c
nulltest.c: In function ‘NULL_as_int’:
nulltest.c:6:12: warning: return makes integer from pointer without a cast
[-Wint-conversion]
     return NULL;
            ^~~~
$ 


But if you pass -c to defer linking, the bug manifests:

$ gcc nulltest.c -c
$