[GHC] #14226: Common Block Elimination pass doesn't eliminate common blocks

[GHC]

#14226: Common Block Elimination pass doesn't eliminate common blocks
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.1
  (CodeGen)                          |
      Resolution:  fixed             |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9157             |  Differential Rev(s):  Phab:D3973,
       Wiki Page:                    |  Phab:D3999
-------------------------------------+-------------------------------------

Comment (by AndreasK):

 Replying to [comment:14 bgamari]:
 > This should now be resolved.
 >

 > Rather, I think we could improve the `switch` lowering: currently we
 lower this as a chain of branches. I suspect this is the sort of case
 where we might benefit from instead using a jump table.
 >
 > Measuring this idea and, if it pays off, implementing it might be an
 interesting project for someone looking to get their hands dirty in the
 NCG.

 According to the comments in `CmmSwitch.hs` jump tables only make sense
 when the gaps between entries are smaller than 7 and the table has at
 least 5 elements which isn't the case here.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14226#comment:21>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler