[GHC] #14790: eqTypeRep does not inline

[GHC]

#14790: eqTypeRep does not inline
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.1-alpha2
      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:                    |
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Comment (by dfeuer):

 mpickering, I get a bunch of things that look like this:

 {{{#!hs
 Considering inlining: eqTypeRep
   arg infos [TrivArg, TrivArg]
   interesting continuation CaseCtxt
   some_benefit True
   is exp: True
   is work-free: True
   guidance IF_ARGS [52 128] 210 0
   discounted size = 180
   ANSWER = NO
 }}}

 The continuation, some_benefit, and work-free lines all look good. I don't
 know how to read the guidance line. Has GHC allowed `eqTypeRep` to get too
 large to inline in most cases? If its decisions seem reasonable to you and
 other experienced folks, perhaps we should do something like

 {{{#!hs
 typeRepsSame :: forall k1 k2 (a :: k1) (b :: k2).
              TypeRep a -> TypeRep b -> Bool
 typeRepsSame a b = typeRepFingerprint a == typeRepFingerprint b

 eqTypeRep :: forall k1 k2 (a :: k1) (b :: k2).
              TypeRep a -> TypeRep b -> Maybe (a :~~: b)
 eqTypeRep a b
   | typeRepsSame a b = Just (unsafeCoerce# HRefl)
   | otherwise        = Nothing
 {-# INLINE eqTypeRep #-}
 }}}

 inlining a very thin wrapper, but I was surprised enough by the choice
 that I figured it might point to a more general inlining heuristic
 problem.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14790#comment:6>
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