Ben Gamari authored Mar 11, 2016 and Ben Gamari committed Mar 12, 2016

makeTrivial is responsible for concocting names during simplification.
Previously, however, it would make no attempt to generate a name that
might be useful to later readers of the resulting Core. Here we add a
bit of state to SimplEnv: a finite depth stack of binders within which
we are currently simplifying. We then derive generated binders from this
context.

See #11676.

Open questions:
  * Is there a better way to accomplish this?
  * Is `maxContextDepth` too large/small?

Test Plan: Validate, look at Core.

Reviewers: austin, simonpj

Reviewed By: simonpj

Subscribers: thomie, simonpj

Differential Revision: https://phabricator.haskell.org/D1970

GHC Trac Issues: #11676