Function jit_block_is_reachable 

pub unsafe extern "C" fn jit_block_is_reachable(
    block: jit_block_t,
) -> c_int

Determine if a block is reachable from some other point in its function. Unreachable blocks can be discarded in their entirety. If the JIT is uncertain as to whether a block is reachable, or it does not wish to perform expensive flow analysis to find out, then it will err on the side of caution and assume that it is reachable.