Ben Gamari authored May 13, 2018 and Ben Gamari committed May 13, 2018

This optimisation level is specifically designed to provide the benefits
of optimisation without the obfuscation that sometimes results.

Test Plan: Validate

Reviewers: simonmar

Reviewed By: simonmar

Subscribers: rwbarton, thomie, carter

Differential Revision: https://phabricator.haskell.org/D4675