[GHC] #9358: Improve flag description in the user guide

[GHC]

#9358: Improve flag description in the user guide
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              Reporter:  jstolarek   |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  low         |        Milestone:  7.10.1
             Component:              |          Version:  7.8.3
  Documentation                      |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:              |       Blocked By:
  Documentation bug                  |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by jstolarek):

 I just checked the source code and `-fmax-simplifier-iterations` default
 value is 4. Using `-Odph` bumps it to 20.

 Another issue:
   - Both 4.20 and 4.20.1 mention the incorrect `-fmax-relevant-bindings`
 flag name. The correct is `-fmax-relevant-binds`

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9358#comment:2>
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