[Bug c++/83504] New: incorrect attribute const interpretation on function overloads

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83504

            Bug ID: 83504
           Summary: incorrect attribute const interpretation on function
                    overloads
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

When another overload of a function is subsequently declared const, all
versions of GCC treat calls to a prior overload of the same function as const
and eliminate multiple calls to it with the same argument, even if reads global
memory.  As a result, GCC emits the wrong code for uses of such a function as
in the test case below.

$ cat u.C && gcc -O2 -S -Wall -Wextra -fdump-tree-optimized=/dev/stdout u.C
int i;

int f (int) { return i; }
int __attribute__ ((const)) f ();

void g (void)
{
  i = 0;
  int j = f (0);
  i = 1;

  if (j == f (0))
    __builtin_abort ();
}

;; Function f (_Z1fi, funcdef_no=0, decl_uid=2326, cgraph_uid=0,
symbol_order=1)

f (int D.2325)
{
  int _2;

  <bb 2> [local count: 1073741825]:
  _2 = i;
  return _2;

}



;; Function g (_Z1gv, funcdef_no=1, decl_uid=2329, cgraph_uid=1,
symbol_order=2)

g ()
{
  <bb 2> [local count: 1073741825]:
  i = 1;
  return;

}