[Bug tree-optimization/110361] [13/14 Regression] Missed Dead Code Elimination when using __builtin_unreachable since r13-2020-g16b013c9d9b

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110361

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-08-07
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

What is interesting is we have:
```
  <bb 7> [local count: 525923045]:
  g = &p;
  f.0_18 = f;
  if (f.0_18 == 0)
    goto <bb 8>; [50.00%]
  else
    goto <bb 13>; [50.00%]

  <bb 9> [local count: 225485782]:
  g = &p;
  f.0_36 = f;
  if (f.0_36 == 0)
    goto <bb 8>; [50.00%]
  else
    goto <bb 13>; [50.00%]

```
Those bb's are exactly the same.

Their pred bbs are:
```
  <bb 3> [local count: 751619280]:
  if (e.4_19 == &a)
    goto <bb 9>; [30.00%]
  else
    goto <bb 4>; [70.00%]

  <bb 4> [local count: 526133498]:
  if (e.4_19 == &d)
    goto <bb 7>; [99.96%]
  else
    goto <bb 5>; [0.04%]
```

Their succ branch (that matters) is:
```
  <bb 13> [local count: 375914866]:
  c = &m;
  m ={v} {CLOBBER(eol)};
  _22 = e.4_19 == &d;
  _1 = e.4_19 == &a;
  _23 = _1 | _22;
  if (_23 != 0)
    goto <bb 12>; [25.16%]
  else
    goto <bb 10>; [74.84%]
```

So coming into bb13, we know that `(e.4_19 == &d) | (e.4_19 == &a)` is true.
Removing the branch to bb 10 which was the call to foo:
  <bb 10> [local count: 281323581]:
  foo ();