[GHC] #10397: Compiler performance regression 7.6 -> 7.8 in elimCommonBlocks

[GHC]

#10397: Compiler performance regression 7.6 -> 7.8 in elimCommonBlocks
-------------------------------------+-------------------------------------
        Reporter:  TobyGoodwin       |                   Owner:
            Type:  bug               |                  Status:  patch
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.8.4
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |  performance
 Type of failure:  None/Unknown      |            Architecture:
      Blocked By:                    |  Unknown/Multiple
 Related Tickets:                    |               Test Case:  see ticket
                                     |                Blocking:
                                     |  Differential Revisions:  Phab:D892
-------------------------------------+-------------------------------------

Comment (by nomeata):

 While working on this I found another bottleneck in the code generator,
 #10422. With that fixed¹ as well, we go from

 > <<ghc: 97671622904 bytes, 3397 GCs, 80319390/302142488 avg/max bytes
 residency (30 samples), 788M in use, 0.001 INIT (0.001 elapsed), 131.423
 MUT (143.189 elapsed), 9.869 GC (9.877 elapsed) :ghc>>

 to

 > <<ghc: 41423234208 bytes, 2190 GCs, 77441625/272967128 avg/max bytes
 residency (38 samples), 750M in use, 0.001 INIT (0.001 elapsed), 31.470
 MUT (42.974 elapsed), 13.051 GC (13.059 elapsed) :ghc>>


 Yay!

 ¹ patch pending validation, maybe I accidentially broke everything

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10397#comment:13>
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