[Bug tree-optimization/121493] New: Another missing Fre from a copy

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121493

            Bug ID: 121493
           Summary: Another missing Fre from a copy
           Product: gcc
           Version: 16.0
            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: ---

Testcase:
```

struct s1
{
  int t;
};

struct s2
{
  struct s1 t;
};

int f1(int a)
{
  s1 t{a};
  s2 tt{t};
  s2 ttt = tt;
  s1 *t0 = &ttt.t;
  return t0->t;
}

int f2(int a)
{
  s1 t{a};
  s2 tt{t};
  s2 ttt = tt;
  return ttt.t.t;
}
```

Compile with `-O2 -fno-tree-sra` and see that f1 is not able to optimize to
just `return a`. While f2 is.
The only difference between the two at fre1 is:
  _7 = MEM[(struct s1 *)&ttt].t;
vs:
  _6 = ttt.t.t;

Noticed this while looking into PR 92811 if we disable SRA.