[GHC] #12437: 20% regression in max_bytes_used for T1969

[GHC]

#12437: 20% regression in max_bytes_used for T1969
-------------------------------------+-------------------------------------
           Reporter:  simonmar       |             Owner:  osa1
               Type:  bug            |            Status:  new
           Priority:  highest        |         Milestone:  8.2.1
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 This is 20% worse:

 {{{
 =====> T1969(normal) 1 of 1 [0, 0, 0]
 cd "./T1969.run" &&  "/data/users/smarlow/ghc/inplace/test   spaces/ghc-
 stage2" -c T1969.hs -dno-debug-output -no-user-package-db -rtsopts -fno-
 warn-missed-specialisations -fshow-warning-groups +RTS -G1 -RTS  +RTS -V0
 -tT1969.comp.stats --machine-readable -RTS
 max_bytes_used value is too high:
     Expected    T1969(normal) max_bytes_used: 15017528 +/-15%
     Lower bound T1969(normal) max_bytes_used: 12764898
     Upper bound T1969(normal) max_bytes_used: 17270158
     Actual      T1969(normal) max_bytes_used: 18071064
     Deviation   T1969(normal) max_bytes_used:     20.3 %
 *** unexpected stat test failure for T1969(normal)
 }}}

 One of these patches is the culprit, but I can't tell from the build logs
 because the build was broken between these two points:

 {{{
 commit 6a4dc891fa7a8024d8f9f03b98ad675ff5fcbd91
 Author: Ömer Sinan Ağacan <omeragacan at gmail.com>

     Bump Haddock submodule

 commit 8d4760fb7b20682cb5e470b24801301cfbbdce3b
 Author: Simon Peyton Jones <simonpj at microsoft.com>

     Comments re ApThunks + small refactor in mkRhsClosure

 commit 9c54185b26922d88e516942aad946f05f707d7ce
 Author: Simon Peyton Jones <simonpj at microsoft.com>

     Comments + tiny refactor of isNullarySrcDataCon

 commit a09c0e3e68c96882a1fb392c9dbeea84056bf32f
 Author: Simon Peyton Jones <simonpj at microsoft.com>

     Comments only

 commit 714bebff44076061d0a719c4eda2cfd213b7ac3d
 Author: Ömer Sinan Ağacan <omeragacan at gmail.com>

     Implement unboxed sum primitive type
 }}}

 The patch immediately preceding this sequence does not have the failure:
 https://phabricator.haskell.org/rGHC83e4f49577665278fe08fbaafe2239553f3c448e
 (follow the link to the build)

 and the final patch in this sequence *does* have the failure:
 https://phabricator.haskell.org/rGHC6a4dc891fa7a8024d8f9f03b98ad675ff5fcbd91
 (along with an improvement in T9675)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12437>
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