[GHC] #12071: PowerPC: RTS SMP functions lack memory barriers

[GHC]

#12071: PowerPC: RTS SMP functions lack memory barriers
-------------------------------------+-------------------------------------
           Reporter:  trommler       |             Owner:  trommler
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.0.2
          Component:  Runtime        |           Version:  8.0.1
  System                             |
           Keywords:  PowerPC SMP    |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Runtime crash
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
  concurrent/prog001/concprog001     |
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 @hvr reported on POWER7 big endian (powerpc64) and on AIX (powerpc):
 {{{
 internal error: END_TSO_QUEUE object entered!
 (GHC version 8.0.0.20160421 for powerpc64_unknown_linux)
 }}}

 Also `concprog001` segfaults, which I falsely attributed to #11259 (no
 runtime linker support) when I marked the test broken on powerpc64.

 I propose to use gcc and clang `_sync_*` built-ins that are already used
 in `libraries/ghc-prim/cbits/atomic.c` instead of CPP ifdefs and inline
 assembly.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12071>
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