[GHC] #11791: Remove the `isInlinePragma prag` test

[GHC]

#11791: Remove the `isInlinePragma prag` test
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           Reporter:  nomeata        |             Owner:
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #11781, #5928
Differential Rev(s):                 |         Wiki Page:
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 This is a spin off of tickjet:11781#comment:9, where simonpjs writes:

 > What is more mysterious to me is why the unfolding for
 `$fApplicativeIO_$c*>` doesn't have `bindIO`, and then `bindIO` inlined
 into it, which would allow a cascade of further improvements, which would,
 I think, produce essentially the same code as `thenIO`.
 >
 > The offending corner is this
 > {{{
 > active_unfolding_gentle id
 >   =  isInlinePragma prag    -- WHY??
 >   && isEarlyActive (inlinePragmaActivation prag)
 > }}}
 > So I tried removing the `isInlinePragma prag` test, and indeed the code
 becomes identical.
 >
 > Conclusion:
 > * I'd love to make the above change to `active_unfolding_gentle` and see
 if any other performance numbers budge.  I doubt that anything will change
 a lot -- it really only affects whether optimisation happens before or
 after inlining -- but it should improve compiler performance a bit for
 that very reason.  This could be a separate ticket
 >
 > Incidentally, see #5928 which is somewhat related.

 This ticket tracks that idea.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11791>
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