[GHC] #13604: regression in ghc 8.2.1-rc1 (8.2.0.20170404)

[GHC]

#13604: regression in ghc 8.2.1-rc1 (8.2.0.20170404)
-------------------------------------+-------------------------------------
        Reporter:  George            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  GHCi              |              Version:  8.2.1-rc1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by ezyang):

 So, the motivating principle for the change in behavior for `ghc --make`
 is that, if you run a `ghc` command, the end result should always be the
 same as if you had run GHC on a clean project. This means that, yes, if
 the optimization level changed, you better recompile your files.

 I don't think this is necessarily what GHCi users are looking for. Without
 `-fobject-code`, optimization level doesn't matter at all and I can
 definitely see an argument for the semantics, "Please ignore my flags and
 use the on-disk compiled products as much as possible, so long as they
 accurately reflect the source code of my program." This interpretation is
 supported by the fact that `-O` flag doesn't do anything right now. (But,
 it is probable that `-fobject-code` should shunt us back into the `--make`
 style semantics.)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13604#comment:11>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler