[GHC] #9349: excessive inlining with -fpre-inlining

[GHC]

#9349: excessive inlining with -fpre-inlining
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        Reporter:  rwbarton                 |            Owner:
            Type:  bug                      |           Status:  new
        Priority:  normal                   |        Milestone:
       Component:  Compiler                 |          Version:  7.8.3
        Keywords:                           |     Differential:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  Runtime performance bug  |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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 The program at https://gist.github.com/jorendorff/a3005968adc8f054baf7
 runs very slowly when compiled with `-O` or higher. It seems that `arr`
 and/or `rangeMap` is being inlined into the do block on lines 89-91 and
 recomputed for each iteration of the loop. The program runs nearly
 instantly when compiled with `-O0` or with `-O -fno-pre-inlining`. (Of
 course, this does not mean `-fpre-inlining` is necessary the culprit; it
 could be enabling some subsequent misoptimization.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9349>
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