Note [Dead ends]

We call an expression that either diverges or throws a precise or imprecise
exception a "dead end". We used to call such an expression just "bottoming",
but with the measures we take to preserve precise exception semantics
(see Note [Precise exceptions and strictness analysis]), that is no longer
accurate: 'exnDiv' is no longer the bottom of the Divergence lattice.

Yet externally to demand analysis, we mostly care about being able to drop dead
code etc., which is all due to the property that such an expression never
returns, hence we consider throwing a precise exception to be a dead end.
See also 'isDeadEndDiv'.