[GHC] #14208: Performance with O0 is much better than the default or with -O2, runghc performs the best

[GHC]

#14208: Performance with O0 is much better than the default or with -O2, runghc
performs the best
-------------------------------------+-------------------------------------
        Reporter:  harendra          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      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:                    |
-------------------------------------+-------------------------------------

Comment (by harendra):

 I measured runghc vs ghc performance for this test case on 7.10.3, 8.0.2
 and 8.2.1. It seems runghc has always been faster, though the difference
 was not much in 7.10.3, runghc seems to have improved a lot in 8.0
 performing better than ghc.

 {{{
 7.10.3 ghc      : time                 11.43 ms   (11.05 ms .. 11.75 ms)
 7.10.3 runghc   : time                 10.55 ms   (9.461 ms .. 11.46 ms)

 8.0.2 ghc       : time                 11.00 ms   (10.64 ms .. 11.38 ms)
 8.0.2 runghc    : time                 6.441 ms   (6.025 ms .. 6.790 ms)

 8.2.1 ghc (O0)  : time                 8.986 ms   (8.728 ms .. 9.313 ms)
 8.2.1 runghc    : time                 4.598 ms   (4.350 ms .. 4.890 ms)
 }}}

 It will be awesome if ghc can be as good as runghc.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14208#comment:9>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler