[GHC] #10676: silly assembly for comparing the result of comparisons that return Int# against 0#

[GHC]

#10676: silly assembly for comparing the result of comparisons that return Int#
against 0#
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        Reporter:  rwbarton          |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.1
  (CodeGen)                          |
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:  x86_64
 Type of failure:  Runtime           |  (amd64)
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by rwbarton):

 Yes, I think so. But there is a problem besides the fact that the heap
 check is duplicated. Referring to the Cmm listing in #8326, something
 seems to think that `_sEV` (the 0#-or-1# result of the primop) is live in
 the alternatives, even to the point of passing it through the GC, when
 really it will never be used after the branch. I think that's the reason
 that later passes are unable to avoid this ugly
 `cmp/setCC/movzbl/test/jne` sequence. Otherwise the definition of `_sEV`
 would be inlined at its only use site, the branch, and the code generator
 would then generate a nice `cmp/jCC` sequence.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10676#comment:3>
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