[GHC] #11179: Allow plugins to access "dead code"

[GHC]

#11179: Allow plugins to access "dead code"
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        Reporter:  lerkok            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
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 gridaphobe):

 I looked into this briefly a while ago, and IIRC the first option may be
 as simple as removing the call to `simpleOptPgm` inside `Desugar.deSugar`.
 Or, rather, moving it to an initial Core2Core pass, which would preserve
 the current pipeline but cleanly allow plugins access to the fully
 unoptimized program.

 There's a warning right before the call though, that suggests the
 unoptimized program may be excessively large. I don't know how much of a
 concern this would be in practice.

 The other thing to consider is whether removing the initial optimization
 pass may break existing Core2Core plugins. If a plugin inserts itself at
 the beginning of the Core2Core pipeline, the overall order would change
 from

 {{{
   simpleOptPgm > plugin > ...
 }}}

 to

 {{{
   plugin > simpleOptPgm > ...
 }}}

 For some plugins, e.g. Levent's or LiquidHaskell, this is exactly what is
 desired, but it could break others.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11179#comment:8>
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