[GHC] #13220: Performance regressions in testsuite from join points

[GHC]

#13220: Performance regressions in testsuite from join points
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        Reporter:  lukemaurer        |                Owner:  lukemaurer
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:  JoinPoints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 Okay, found the REAL culprit. It's embarrassingly simple, and not at all
 what I had been looking for.

 Running `ghc` with `-dcore-lint -v` and grepping for `Core Linted result`
 revealed the issue, this new line in `simplifyPgmIO`:
 {{{#!diff
             Err.dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence
 analysis"
                       (pprCoreBindings tagged_binds);
 +           lintPassResult hsc_env CoreOccurAnal tagged_binds;

                  -- Get any new rules, and extend the rule base
                  -- See Note [Overall plumbing for rules] in Rules.hs
 }}}
 We now run Core Lint twice per simplifier iteration, which in my sample
 program amounted to running Core Lint 50% more times overall. That's
 rather expensive.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13220#comment:28>
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