Simplify trivial constants in SimplifyConstCondition After `InstSimplify-after-simplifycfg` with `-Zub_checks=false`, there are many of the following patterns. ``` _13 = const false; assume(copy _13); _12 = unreachable_unchecked::precondition_check() -> [return: bb1, unwind unreachable]; ``` Simplifying them to unreachable early should make CFG simpler.