[GHC] #8205: the 'impossible' happened : expectJust block_order

[GHC]

#8205: the 'impossible' happened : expectJust block_order
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        Reporter:  erikd                |            Owner:  jstolarek
            Type:  bug                  |           Status:  new
        Priority:  normal               |        Milestone:
       Component:  Compiler             |          Version:  7.7
      Resolution:                       |         Keywords:
Operating System:  Unknown/Multiple     |     Architecture:
 Type of failure:  Building GHC failed  |  Unknown/Multiple
       Test Case:                       |       Difficulty:  Unknown
        Blocking:                       |       Blocked By:
                                        |  Related Tickets:
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Changes (by jstolarek):

 * cc: kazu@… (added)


Comment:

 OK, I understand why this happens only on some systems. This is related to
 splliting proc points, which is turned on by this piece of code in
 !CmmPipeline:

 {{{
 splitting_proc_points = hscTarget dflags /= HscAsm
                      || not (tablesNextToCode dflags)
                      || -- Note [inconsistent-pic-reg]
                         usingInconsistentPicReg
 usingInconsistentPicReg
       = case (platformArch platform, platformOS platform, gopt Opt_PIC
 dflags)
         of   (ArchX86, OSDarwin, pic) -> pic
              (ArchPPC, OSDarwin, pic) -> pic
              _                        -> False
 }}}

 If I turn on splitting proc-points by simply setting
 `splitting_proc_points = True` I still can't reproduce the bug because Cmm
 is transformed in a different way on my architecture (namely, cFXS block
 is not removed). I have an idea how to fix this, but this will be
 speculative. Kazu, I will need your help in testing the patch once it is
 ready.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8205#comment:18>
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