[GHC] #13654: Optimize casMutVar# for single-threaded runtime

[GHC]

#13654: Optimize casMutVar# for single-threaded runtime
-------------------------------------+-------------------------------------
           Reporter:  dfeuer         |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:  8.4.1
          Component:  Runtime        |           Version:  8.2.1-rc1
  System                             |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Runtime
  Unknown/Multiple                   |  performance bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 When using the non-threaded RTS, `stg_casMutVarzh`,
 `stg_atomicModifyMutVarzh`, etc., shouldn't need to actually use atomic
 instructions, but they seem to do so. I believe this makes them
 substantially slower than necessary in that context.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13654>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler