https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112542
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2023-11-15
Ever confirmed|0 |1
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
```
_7 = (char) c.2_5;
...
_26 = _7 == 0;
_27 = c.2_5 == 0;
_28 = _26 & _27;
if (_28 != 0)
```
we transform this into:
```
_26 = _7 == 0;
_27 = c.2_5 == 0;
if (c.2_5 == 0)
```
During FRE1
Which is correct. and _26 goes away later on.
Then in evpr GCC changes:
```
# iftmp.8_29 = PHI <_7(4), 0(5)>
```
into:
```
# iftmp.8_29 = PHI <-1(4), 0(5)>
```
Which is also correct.
Where it goes wrong is vrp1.
We end up with this mess:
```
b.0_1 = b;
_2 = b.0_1 == 0;
_4 = (int) _2;
c = _4;
i.7_12 = (unsigned int) _2;
_16 = b.0_1 != 0;
_15 = _16 ? 1 : 2;
if (_15 == 2)
goto <bb 3>; [0.00%]
else
goto <bb 4>; [100.00%]
<bb 3> [count: 0]:
__builtin_unreachable ();
```
But that is basically:
```
...
if (b.0_1 == 0) __builtin_unreachable();
```
