[GHC] #12274: GHC panic: simplifier ticks exhausted

[GHC]

#12274: GHC panic: simplifier ticks exhausted
-------------------------------------+-------------------------------------
        Reporter:  mrkkrp            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  Compile-time      |  (amd64)
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by thomie):

 * failure:  Compile-time crash => Compile-time performance bug


Comment:

 Some notes:

 * There are a lot of `INLINE` pragmas in `Text.Mustache.Parser`, maybe too
 many? For example, removing the `INLINE` on `symbol` fixes the panic.

 * A `simpl-tick-factor` of `110` fixes the panic, so the simplifier is
 going only very slightly over the limit. This is probably nothing to worry
 about.

 * The regression in compile time is the real problem. Fixing it will fix
 the panic as well. I reduced it to the following testcase:
 https://github.com/thomie/megaslow (no external dependencies).

 Instructions:
 {{{
 $ ghc -O Char.hs
 $ ghc -O -c -Rghc-timing Test.hs
 }}}


 ||= GHC =||= Bytes allocated for `Test.hs` =||
 || 7.8.4 || 117MB ||
 || 7.10.3 || 750MB ||
 || HEAD (ffe4660510a7ba4adce846f316db455ccd91142a) || 724MB ||

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12274#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler