[Bug middle-end/101791] New: missing warning on a mismatch between scalar and array forms of new and delete

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101791

            Bug ID: 101791
           Summary: missing warning on a mismatch between scalar and array
                    forms of new and delete
           Product: gcc
           Version: 12.0
            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: ---

The -Wmismatched-new-delete warning introduced in GCC 11 is meant to diagnose
calls to operator delete with pointers obtained from a mismatched form or
overload of operator new.  A poster child for such a mismatch is the scalar
form of a delete expression with an argument obtained from array new.  GCC 11
diagnoses such mismatches when they involve member operators new and delete (as
in g() below) but it fails to do the same for the default non-member operators
(as in h()).

$ cat t.C && gcc -S -Wall t.Ctypedef __SIZE_TYPE__ size_t;

struct A
{
  void* operator new (size_t);
  void operator delete (void*);

  void* operator new[] (size_t);
  void operator delete[] (void*);
};

void f (void*);

void g ()
{
  A *p = new A[7];
  f (p);
  delete p;        // -Wmismatched-new-delete (good)
}

void h ()
{
  int *p = new int[7];
  f (p);
  delete p;        // missing warning
}
t.C: In function ‘void g()’:
t.C:18:10: warning: ‘static void A::operator delete(void*)’ called on pointer
returned from a mismatched allocation function [-Wmismatched-new-delete]
   18 |   delete p;        // -Wmismatched-new-delete (good)
      |          ^
t.C:16:17: note: returned from ‘static void* A::operator new [](size_t)’
   16 |   A *p = new A[7];
      |                 ^