[GHC] #14610: newtype wrapping of a monadic stack kills performance

[GHC]

#14610: newtype wrapping of a monadic stack kills performance
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        Reporter:  mrkkrp            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      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):

 >  So it looks like newtype wrapping reduces GHC's ability to create join
 points SPJ talked about recently.

 Without looking at the code: This is a good guess. `foo x = if … then foo
 (x+1) else …` is a tail call (and hence allows `foo` to be a join point)
 while `foo x = if … then foo (x+1) `cast` coercion … else …` is not. But
 (from an operational point of view) it could well be!

 But someone would have to produce a minimal example to be sure this is
 really the issue.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14610#comment:2>
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