[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):

 From ghc-devs:

 jstolarek:
 > How can I observe the effects of `-ddump-simpl-phases`? I tried
 compiling several different programs and this flag seems to have no effect
 (ie. nothing gets printed).

 simonpj:
 > I had to read the source code.  I think you say
 >        "-ddump-simpl-phases=A,B,C"
 > to dump the output of phases called A,B,C. But no, it seems that it only
 affects output of simplifier statistics (see simplifyPgmIO).  I have never
 used this flag.  Maybe it can go.  Looks strange to me.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9358#comment:3>
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