[GHC] #10720: New GHC fails to specialize imported function

[GHC]

#10720: New GHC fails to specialize imported function
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              Reporter:  wyager      |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.2
              Keywords:              |  Operating System:  MacOS X
  performance, inline, specialize    |
          Architecture:  x86_64      |   Type of failure:  Runtime
  (amd64)                            |  performance bug
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
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 I just installed the new Haskell platform for OS X.

 It seems to have caused a major performance regression for a program I'm
 working on, making it well over 25x slower.

 The culprit appears to be that the new GHC (7.10.2) fails to specialize an
 imported function. If I manually add a SPECIALIZE pragma, performance goes
 back to around what it used to be.

 The code in question is located at https://github.com/wyager/HNet .

 As it stands, the code takes about 30 seconds to run on my machine. With
 the previous haskell-platform, it only took about .9 seconds.

 If I modify Operations.hs and uncomment the SPECIALIZE pragma, runtime
 goes down to about 1.1 seconds (still slower for some reason, but not
 awful).

 To test, compile with -O2 (as the program makes heavy use of Data.Vector,
 which requires -fspec-constr for performance).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10720>
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