Function is_tautology 

fn is_tautology(
    ty: ElementaryType,
    val_neg: bool,
    val_mag: U256,
    op: BinOpKind,
) -> bool

Returns true if var <op> val is always true or always false for every value in the type’s range.

The constant is represented as a sign bit (val_neg) and a magnitude (val_mag), matching how solar stores negated literals (e.g. -128 -> Unary(Neg, Lit(128))).