[Bug tree-optimization/110932] [14 Regression] Dead Code Elimination Regression since r14-2230-g7e904d6c7f2

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110932

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-08-19

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
  _41 = _43 <= 0;
  # RANGE [irange] unsigned short [0, 1] NONZERO 0x1
  _40 = (unsigned short) _41;
  # RANGE [irange] unsigned short [65534, +INF]
  _36 = ~_40;
  # RANGE [irange] short int [-2, -1]
  _19 = (short intD.17) _36;
  # RANGE [irange] unsigned int [4294967294, +INF]
  _17 = (unsigned intD.9) _19; // ~(unsigned)_41
   // rather _41 ? 4294967294 : 4294967295
  i.1_14 = (unsigned intD.9) pretmp_60;
  _13 = i.1_14 < _17;
  # RANGE [irange] int [0, 1] NONZERO 0x1
  _12 = (intD.6) _13;
  if (_12 == pretmp_60)


pretmp_60 == (((unsigned intD.9) pretmp_60) < _17)

Which is:
(pretmp_60  == 1 && ((unsigned intD.9) pretmp_60) < _17))
| (pretmp_60  == 0 && ((unsigned intD.9) pretmp_60) >= _17))
Though ((unsigned intD.9) pretmp_60) >= _17) is always false because _17's
range does not include 0.

So we are left with:
(pretmp_60  == 1 && 1 < _17)
But _17's range is always bigger than 0 so we are just left with:
pretmp_60 == 1


So the general rule is:
(simplify
 (eq:c @0 (convert (cmp @1 @2)))
 (if (bitwise_equal_p (@0, @1))
 (with {
    bool zeroalwaystrue = ...
    bool zeroalwaysfalse = ...
    bool onealwaystrue = ...
    bool onealwaysfalse = ...
  }
  (switch
   (if (zeroalwaystrue && onealwaystrue)
    (le @0:unsigned { one(unsigned); } )) // @0 == 0 | @0 == 1
   (if (zeroalwaysfalse && onealwaysfalse )
    { false_bool; }) // false
   (if (zeroalwaystrue && onealwaysfalse)
    (eq @0 { zero(TREE_TYPE(@0)); })) // @0 == 0
   (if (onealwaystrue && onealwaysfalse)
    (eq @0 { one(TREE_TYPE(@0)); })) // @0 == 1

Later on instead of `if (_12 == _50)` we would have `if (_50 == 1)`
```
  if (_50 == 1)
    goto <bb 4>; [51.12%]
  else
    goto <bb 3>; [48.88%]
...
  <bb 4> [local count: 278223726]:
  if (_50 != 0)
    goto <bb 5>; [33.00%]
  else
    goto <bb 15>; [67.00%]
```
Which is an obvious case where we know _50 is 1 in bb 4 and therefore !=0.
etc.