[GHC] #13044: make it possible to apply GHC rewrite rules to class methods

[GHC]

#13044: make it possible to apply GHC rewrite rules to class methods
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        Reporter:  George            |                Owner:
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nomeata):

 Currently, rewrite rules, as well as unfolding (i.e. inlining) are active
 in certain phases, which are currently counted down from, I belive, 3 to
 0. Exending this system of phases to something more expressive has always
 been a thought. Maybe it would help here?

 The smallest delta that might help is simply adding a a number of extra
 phases, say, from 7 to 4. The compiler would annotate all type class
 dictionary access functions (i.e. class methods) with `INLINE [~4]`, which
 would prevent them from being rewritten to the actual implementation. Then
 rewrite rules active in phases 7, 6 and 5 would have a pretty good chance
 of applying to class methods.

 Would this work?

 Obviously, one might want nicer ways of specifying phases (i.e. fixed
 names, or even arbitrary news with ordering constraints), but that is a
 slightly orthogonal discussion.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13044#comment:5>
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