Simon Peyton Jones authored Feb 28, 2017 and David Feuer committed Feb 28, 2017

C.f. Trac #13286, #13236

* Never destroy a join point unless it goes to top level
  See Note [Floating join point bindings]

* Never float a MFE if it has a free join variable
  Note [Free join points]

* Stop treating nullary join points specially

* Enforce the invariant that le_join_ceil >= le_ctxt_lvl
  (Needs more thought...)

Reviewers: austin, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D3199