[Bug middle-end/98989] New: missing -Wfree-nonheap-object freeing std::strings over 15 bytes long

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98989

            Bug ID: 98989
           Summary: missing -Wfree-nonheap-object freeing std::strings
                    over 15 bytes long
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

Given the test case below, -Wfree-nonheap-object detects the invalid attempt to
free the std::string buffer provided the string constant it's initialized with
is no more than 15 characters long (plus the terminating nul).  But the option
fails to diagnose the invalid call once the string length is 16 or more.

#include <string>

void f ()
{
  std::string str (STR);
  char *p = &str[0];
  free (p);
}

$ g++ -DSTR='"abcdefghijklmno"' -O2 -S -Wall t.C
t.C: In function ‘void f()’:
t.C:7:8: warning: ‘void free(void*)’ called on unallocated object ‘str’
[-Wfree-nonheap-object]
    7 |   free (p);
      |   ~~~~~^~~
t.C:5:15: note: declared here
    5 |   std::string str (STR);
      |               ^~~