[Bug c++/108646] New: nonnull attribute does not detect variables that are NULL being passed

["jg at jguk dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108646

            Bug ID: 108646
           Summary: nonnull attribute does not detect variables that are
                    NULL being passed
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jg at jguk dot org
  Target Milestone: ---

If we pass NULL directly, there is a good warning (pasted below from today on
Godblot.org latest gcc trunk)

However, there is no error if passing a variable set to NULL.
Could gcc detect this situation?



#include <cstddef>
void * mem2(void *dest) __attribute__((nonnull));
void test(void)
{
 char *dest = NULL;
 mem2(dest); 
 }



This is the warning when NULL is passed directly:

<source>: In function 'void test()':
<source>:6:6: warning: argument 1 null where non-null expected [-Wnonnull]
    6 |  mem2(NULL);
      |  ~~~~^~~~~~
<source>:2:8: note: in a call to function 'void* mem2(void*)' declared
'nonnull'
    2 | void * mem2(void *dest) __attribute__((nonnull));
      |        ^~~~
Compiler returned: 0