[GHC] #9425: ghc-HEAD (only in -O -fllvm aka 'optllvm') prunes yield in -fno-omit-yields mode

[GHC]

#9425: ghc-HEAD  (only in -O -fllvm aka 'optllvm') prunes yield in -fno-omit-
yields mode
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              Reporter:  slyfox      |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.2
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by rwbarton):

 LLVM assumes that `HpLim` (which is located at `0x358(%r13)`) is not
 changing during the loop. We need to emit whatever LLVM assembly language
 construction tells LLVM to assume that `HpLim` might change (`load
 volatile` perhaps?)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9425#comment:2>
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