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

[GHC]

#13745: Investigate compile-time regressions in regex-tdfa-1.2.2
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  high              |            Milestone:  8.2.2
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             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:                    |
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Comment (by dfeuer):

 Going from 8.0.2 to 8.2.1, things look very different right near the
 beginning, presumably as a result of the early inline patch. In 8.0.2, the
 first simplifier pass gives

 {{{
 *** Simplifier [TextRegexTDFANewDFAEngine_FA]:
 Result size of Simplifier iteration=1
   = {terms: 6,220, types: 14,606, coercions: 1,563}
 }}}

 whereas in 8.2.1 it gives

 {{{
 *** Simplifier [TextRegexTDFANewDFAEngine_FA]:
 Result size of Simplifier iteration=1
   = {terms: 17,641, types: 38,397, coercions: 10,258, joins: 30/233}
 }}}

 Things remain pretty bad until after float out, when they first get
 surprisingly good and then sort of oscillate. I'll take a look at the
 differences across the commits Ryan points out.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13745#comment:8>
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