[GHC] #9320: Inlining regression/strangeness in 7.8

[GHC]

#9320: Inlining regression/strangeness in 7.8
-------------------------------------+-------------------------------------
        Reporter:  dolio             |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.8.2
      Resolution:                    |             Keywords:  Inlining
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:                    |
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Comment (by nfrisby):

 FYI, with GHC 7.10.2, both `-O1` and `-O2` give code where `test0` takes
 80x as much time as does `test1`.

 {{{
 $ uname -a
 Linux sci-host-a-i-bd1bec66 3.13.0-100-generic #147-Ubuntu SMP Tue Oct 18
 16:48:51 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
 $ ghc --version
 The Glorious Glasgow Haskell Compilation System, version 7.10.2
 $ ghc -fforce-recomp -O2 --make Main.hs
 $ time ./Main 500000 True; time ./Main 500000 False
 1

 real    0m4.703s
 user    0m4.682s
 sys     0m0.020s
 1

 real    0m0.055s
 user    0m0.051s
 sys     0m0.004s
 $ echo '4.7 / 0.055' | bc -l
 85.45454545454545454545
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9320#comment:5>
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