[GHC] #8774: Transitivity of Auto-Specialization

[GHC]

#8774: Transitivity of Auto-Specialization
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        Reporter:  crockeea          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.6.3
      Resolution:                    |             Keywords:  Inlining
Operating System:  Linux             |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #5928, #8668,     |  Differential Rev(s):
  #8099                              |
       Wiki Page:                    |
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Comment (by erikd):

 Without `SPECIALIZE` it takes about a second on my laptop (month old high
 end Dell with SSD). I simply can't image an x86_64 machine could be over
 60 times slower.

 Ok, so the suspicious code is:
 {{{
             case (Foo.$fNumQux_$c+
                     @ GHC.Types.Int
                     GHC.Num.$fNumInt
                     Data.Vector.Unboxed.Base.$fUnboxInt
                     v1_aHk
                     v2_aHl)
 }}}
 which is what I get with ghc-7.6.3. I get something very similar with
 ghc-7.8.4.

 For ghc 7.10.3 and 8.0.1 there is no instance of the string `GHC.Num` in
 the output from `Main` (but there is for `Foo` which is expected).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8774#comment:15>
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