// llvm/test/Transforms/InstCombine/fabs.ll

```
define double @select_fcmp_nnan_ole_zero(double %x) {
%0:
  %lezero = fcmp ole double %x, 0.000000
  %negx = fsub nnan double 0.000000, %x
  %fabs = select i1 %lezero, double %negx, double %x
  ret double %fabs
}
=>
define double @select_fcmp_nnan_ole_zero(double %x) {
%0:
  %1 = fabs nnan double %x
  ret double %1
}
Transformation doesn't verify!
ERROR: Target is more poisonous than source

Example:
double %x = NaN

Source:
i1 %lezero = #x0 (0)
double %negx = poison
double %fabs = NaN

Target:
double %1 = poison
Source value: NaN
Target value: poison
```

After the transformation, nnan flag should be dropped because %x can be NaN.