Function assume_scalar_range 

fn assume_scalar_range<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
    bx: &mut Bx,
    imm: Bx::Value,
    scalar: Scalar,
    backend_ty: Bx::Type,
    known: Option<&Scalar>,
)

Emits an assume call that imm’s value is within the known range of scalar.

If known is Some, only emits the assume if it’s more specific than whatever is already known from the range of that scalar.