[GHC] #13745: Investigate compile-time regressions in regex-tdfa-1.2.2

22 May 2017


      #13745: Investigate compile-time regressions in regex-tdfa-1.2.2
-------------------------------------+-------------------------------------
           Reporter:  bgamari        |             Owner:  (none)
               Type:  task           |            Status:  new
           Priority:  high           |         Milestone:  8.2.1
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  performance bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 hvr [[https://mail.haskell.org/pipermail/ghc-
 devs/2017-May/014208.html|points out]] that GHC 8.2 takes significantly
 longer to compile `regex-tdfa-1.2.2` than 8.0.2. Interestingly, it seems
 that compiler allocations fell dramatically while compilation time rose.

 {{{
 GHC 8.0.2:

 <>

 GHC 8.2.1:

 <>
 }}}

 == Reproducing ==

 {{{
 $ cabal unpack regex-tdfa-1.2.2
 $ cd regex-tdfa-1.2.2
 $ cabal install --only-dependencies
 $ cabal configure
 $ cabal build
 $ time ghc -idist/build/autogen -O2 Text/Regex/TDFA.hs \
    -XMagicHash -XFlexibleInstances -XMultiParamTypeClasses \
    -XRecursiveDo -XBangPatterns -XRankNTypes -XUnboxedTuples \
    -XFlexibleContexts -XUnliftedFFITypes
 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13745
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