[GHC] #15418: Performance drop 60 times on non-profiling binary

[GHC]

#15418: Performance drop 60 times on non-profiling binary
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        Reporter:  hth313            |                Owner:  (none)
            Type:  bug               |               Status:  infoneeded
        Priority:  high              |            Milestone:  8.8.1
       Component:  Runtime System    |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  MacOS X           |         Architecture:  x86_64
 Type of failure:  Runtime           |  (amd64)
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14414, #9599     |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by osa1):

 To be honest I don't think that'd be helpful. Normally for this I'd start
 with
 comparing Core outputs of the program, with and without profiling flags. I
 think it's very likely that this will be enough to see why profiled
 version is
 faster.

 Btw, looking at the previous comments I realized that we didn't check
 different
 optimisation parameters. One of the reasons why sometimes profiling builds
 are
 faster is because profiling sometimes inhibits some optimisations (as it
 changes Core of the program), and optimisations sometimes make some
 programs
 slower. Could you try building your program without profiling, and with
 different optimisation settings? Please report numbers for:

 - -O0
 - -O1 (default when using cabal)
 - -O2

 If you're using cabal add these to `ghc-options` in your .cabal file.
 Depending
 on the numbers you can then try to disable individual optimisation passes
 (see
 the user manual or man page) etc.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15418#comment:17>
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