[GHC] #5218: Add unpackCStringLen# to create Strings from string literals

[GHC]

#5218: Add unpackCStringLen# to create Strings from string literals
-------------------------------------+-------------------------------------
        Reporter:  tibbe             |                Owner:  thoughtpolice
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.0.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #5877 #10064      |  Differential Rev(s):  Phab:D2443
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by winter):

 Replying to [comment:66 bgamari]:
 > > If we add a new closure type for `ByteArray#`, could it be used in
 runtime also?
 >
 > I'm not sure I follow the suggestion here. What do you mean by "used in
 the runtime"?


 I mean can we change 'ByteArray#' 's representation into just length and
 content (removing the header)?  I think that's not possible due to GC
 expect to see an uniform heap object representation, but i'm not sure
 there's no other way to make it work.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5218#comment:67>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler