[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:  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
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Comment (by michalt):

 Replying to [comment:16 nomeata]:
 > [...]
 > Should they? Does maybe the `_s3YJ::P64 = _s3YJ::P64;` throw CBE off?

 Hmm.. Interesting. I'd expect that with the recent patch from bgamari this
 should be commoned up. Is this the final cmm or is it the input to
 `CmmCommonBlockElim`? (asking because sometimes the sinking pass can
 expose more opportunities for `CmmCommonBlockElim`, but we run sinking
 pass *after* eliminating common blocks; example: #12915)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14226#comment:17>
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