[GHC] #12689: DataCon wrappers get in the way of rules

[GHC]

#12689: DataCon wrappers get in the way of rules
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        Reporter:  nomeata           |                Owner:
            Type:  bug               |               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):

 We might want to look at two separate cases:

  1. The LHS mentions a data con (wrapper) unsaturated, (`fT` above).
  2. The LHS mentions a data con (wrapper) saturated, (`gT` above).

 In the first case, I think we should simply disable the warning. Because
 the wrapper is unsaturated, it will not have been inlined in the code.
 Unsaturation is as good as `NOINLINE`, isn’t it?

 Only in the latter case it matters that, as you write
 > after inlining we get a mess of unboxing etc
 Is really all hope lost that we can match the mess? My gut feeling is that
 it is more promising to not work against the inliner and simplifier, and
 rather let it do its jobs (both on the LHS and the code), and try hard to
 make the matcher smart enough to match the mess.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12689#comment:1>
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