[Bug tree-optimization/116556] New: __builtin_object_size does not handle `ptr + (PHI<4,8>)`, only `PHI`

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116556

            Bug ID: 116556
           Summary: __builtin_object_size does not handle `ptr +
                    (PHI<4,8>)`, only `PHI<ptr+4,ptr+8>`
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
void
__attribute__ ((noinline))
test9 (unsigned cond)
{
  char *buf2 = __builtin_malloc (10);
  char *p;
  __SIZE_TYPE__ t;

  if (cond)
    t = 8;
  else
    t = 4;
  p = &buf2[t];

  if (__builtin_object_size (&p[0], 0) != 6)
    __builtin_abort ();
}

void
__attribute__ ((noinline))
test9a (unsigned cond)
{
  char *buf2 = __builtin_malloc (10);
  char *p;
  __SIZE_TYPE__ t;

  if (cond)
    p = &buf2[8];
  else
    p = &buf2[4];

  if (__builtin_object_size (&p[0], 0) != 6)
    __builtin_abort ();
}
```

The __builtin_object_size does not handle the pointer in test9 but does handle
the one in test9a.

This is reduced from gcc.dg/builtin-object-size-1.c when improving phiopt's
factor_out_conditional_operation to handle more than just unary operators.