Note [exprIsCheap] says it decides whether to inline at more than one place

Currently, Note [exprIsCheap] says

By ``cheap'' we mean a computation we're willing to:
        push inside a lambda, or
        inline at more than one place
That might mean it gets evaluated more than once, instead of being
shared.

I think that inline at more than one place is wrong. Git blame reveals that line is from 2011, in which case it probably wasn't updated after May 2012, when Note [exprIsWorkFree] was written, which says:

exprIsWorkFree is used when deciding whether to inline something; we
don't inline it if doing so might duplicate work, by peeling off a
complete copy of the expression.  Here we do not want even to
duplicate a primop (#5623):
   eg   let x = a #+ b in x +# x
   we do not want to inline/duplicate x

Previously we were a bit more liberal, which led to the primop-duplicating
problem.  However, being more conservative did lead to a big regression in
one nofib benchmark, wheel-sieve1.

In general, I'd like to see a chart where we compare the various exprIs{Cheap,WorkFree,HNF,Trivial,OkForSpeculation,...} and maybe state some implications, like "exprIsWorkFree e implicates exprIsCheap e". And if two such functions don't imply each other, provide an example.