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

[GHC]

#14226: Common Block Elimination pass doesn't eliminate common blocks
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.1
  (CodeGen)                          |
      Resolution:                    |             Keywords:
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:                    |
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Comment (by simonpj):

 Ben I forgot to mention this. In `CmmExpr` you'll find
 `foldLocalRegsDefd`, which is, I think, precisely what you need to answer
 the question "which local regs does this node define".  It would be much
 better to use it than to duplicate the logic into `hash_node` and
 `eqMiddleWith`.

 Might you look at doing that?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14226#comment:11>
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