[GHC] #14193: Add RTS flag to disable 1TB address space allocation

[GHC]

#14193: Add RTS flag to disable 1TB address space allocation
-------------------------------------+-------------------------------------
        Reporter:  nh2               |                Owner:  (none)
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9706, #14192     |  Differential Rev(s):  Phab:D3929
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by nh2):

 Replying to [comment:1 simonmar]:
 > adding a flag to disable the large address space would have a
 performance cost, because we'd have to check the flag in the inner loop of
 the GC

 @simonmar do you recall if the impact of this was already measured when
 the new allocator was introduced, or would there be value in me giving it
 a try?

 I have some wishful thinking that if branch prediction and pipelining are
 on our side, we might not be able to measure the additional check -- and
 if it were so I'd welcome the ability to switch it without recompilation
 (of ghc, or even better, the program).

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14193#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler