This function does not by itself prove that two entries are mergeable. Hence, its name is misleading. It's necessary that, for example, the entry is not a submap or in transition. I would like to see those conditions asserted here.

Alternatively, and contradicting my initial comment, giving this function a name like vm_map_simplify_test() would discourage the reuse of this function elsewhere, where the necessary conditions on eflags have not been established.

Now that this code is deindented, this variable is pointless. It's is used once, and computing this value before we know that end == start and the objects match is wasted effort.

vm_map_simplify_deallocate(). Historically, "dispose" functions were simple free operations.

Now that this comment is deindented, the text should be "reflowed".

I'll rename to vm_map_neighbor_test, since 'neighbor' is a term introduced in the comment that describes the 'simplify_entry' function, and 'simplify_test' sounds like we're simplifying some sort of test, which sounds pretty generic.

vm_map_neighbor_deallocate().