[GHC] #7058: Add strict version of modifySTRef

[GHC]

#7058: Add strict version of modifySTRef
-------------------------------------+--------------------------------------
 Reporter:  joeyadams                |          Owner:                  
     Type:  feature request          |         Status:  new             
 Priority:  normal                   |      Component:  libraries/base  
  Version:  7.4.2                    |       Keywords:                  
       Os:  Unknown/Multiple         |   Architecture:  Unknown/Multiple
  Failure:  Runtime performance bug  |       Testcase:                  
Blockedby:                           |       Blocking:                  
  Related:                           |  
-------------------------------------+--------------------------------------
 We added strict versions of modifyIORef and atomicModifyIORef recently
 (see #5926), and STM has
 [http://hackage.haskell.org/packages/archive/stm/latest/doc/html/Control-
 Concurrent-STM-TVar.html#v:modifyTVar-39- modifyTVar'] since stm-2.3.

 This patch adds {{{modifySTRef'}}}, mostly copy-pasted from
 {{{modifyIORef'}}}.  My ghc currently doesn't build, so I wasn't able to
 test it.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7058>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler