[GHC] #13390: Strict literal float-out during desugaring regresses T1969 at -O0

[GHC]

#13390: Strict literal float-out during desugaring regresses T1969 at -O0
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       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 dfeuer):

 I finally built the patched version. As best I can tell, the story starts
 the same. That is, we get the same inlining of `$dme` and `$dmd`, and the
 same class op rules firing, but then `$cc_aT4` is getting inlined into
 `$ce_aTf` and `$cd_aT8` instead of allowing those functions to eta-reduce
 away. So I guess maybe we actually ''can'' make a useful change: perhaps
 we want to check for eta-reduction opportunities ''before'' considering
 inlining. There's not much point inlining a function application into the
 body of a lambda when we can instead eliminate the lambda (and the
 application) altogether.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13390#comment:11>
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