[GHC] #13861: Take more advantage of STG representation invariance (follows up #9291)

[GHC]

#13861: Take more advantage of STG representation invariance (follows up #9291)
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        Reporter:  heisenbug         |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      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 heisenbug):

 Replying to [comment:9 heisenbug]:

 >
 > Probably the motivation was "we'll think about this later".
 Implementation complexity seems to be fairly low, see my branch (caveat:
 ''very WIP'') https://github.com/ggreif/ghc/tree/wip/tag-big-families

 The last checkin does bootstrap GHC and seems to do well not he test side.
 Code still is not as pretty as I want it, but I shall clean it up in the
 next days. Can somebody do a perf evaluation with it? Thanks!

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13861#comment:10>
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