[GHC] #15103: Speed optimizations for elimCommonBlocks

[GHC]

#15103: Speed optimizations for elimCommonBlocks
-------------------------------------+-------------------------------------
        Reporter:  AndreasK          |                Owner:  AndreasK
            Type:  task              |               Status:  patch
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:  CodeGen
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4597
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by AndreasK):

 Replying to [comment:9 simonpj]:
 > Terrific.  Would you like to do a nofib run before-and-after, and dump
 the `nofib-analyse` summary in here?  It's very helpful just to record the
 benefits of particular changes, for posterity.

 {{{
 --------------------------------------------------------------------------------
         Program           Size    Allocs   Runtime   Elapsed  TotalMem
 --------------------------------------------------------------------------------
        maillist           0.0%      0.0%     0.024     0.025     +6.5%
            mate          -0.0%      0.0%     +4.6%     +4.6%      0.0%
    cryptarithm1           0.0%      0.0%     -1.7%     -1.8%      0.0%
 --------------------------------------------------------------------------------
             Min          -0.0%     -0.0%     -1.7%     -1.8%      0.0%
             Max          +0.0%     +0.1%     +4.6%     +4.6%     +6.5%
  Geometric Mean          -0.0%     +0.0%     +0.3%     +0.3%     +0.1%

 Compile Times

 -------------------------------------------------------------------------------
         Program             logNoOpt       logWithOpt
 -------------------------------------------------------------------------------
         -1 s.d.                -----            -1.9%
         +1 s.d.                -----            +1.5%
         Average                -----            -0.2%

 Compile Allocations

 -------------------------------------------------------------------------------
         Program             logNoOpt       logWithOpt
 -------------------------------------------------------------------------------
         -1 s.d.                -----            -0.3%
         +1 s.d.                -----            -0.1%
         Average                -----            -0.2%

 }}}

 These runtime results took me by surprise!

 It turns out code layout depends on uniques. And the final uniques change
 with this patch.
 So we get slightly different codelayout.

 I verified that the code for mate is otherwise the same.
 Using different starting or increment values for uniques also lead to
 different results with up to the same performance spread.
 So I don't think the runtime change is representative.

 Compiler performance impact is as expected.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15103#comment:10>
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