[GHC] #10012: Cheap-to-compute values aren't pushed into case branches inducing unnecessary register pressure

[GHC]

#10012: Cheap-to-compute values aren't pushed into case branches inducing
unnecessary register pressure
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        Reporter:  bgamari           |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.8.4
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 > But what is so special about this case that makes this a worthwhile
 thing here, and not in other cases (sic)? Maybe the heuristics can be
 improved in general?

 I'd also like to point out that we already decide to inline the
 `BuildStep` `k` itself into `ensureRoom/step` (although I admittedly don't
 yet understand why). It seems odd that we would inline this yet not its
 free variables.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10012#comment:11>
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