[GHC] #8199: Get rid of HEAP_ALLOCED

[GHC]

#8199: Get rid of HEAP_ALLOCED
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       Reporter:  ezyang                      |             Owner:  ezyang
           Type:  feature request             |            Status:  new
       Priority:  normal                      |         Milestone:  7.10.1
      Component:  Compiler                    |           Version:  7.7
       Keywords:                              |  Operating System:
   Architecture:  Unknown/Multiple            |  Unknown/Multiple
     Difficulty:  Project (more than a week)  |   Type of failure:
     Blocked By:                              |  None/Unknown
Related Tickets:                              |         Test Case:
                                              |          Blocking:
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 This bug is to track progress of removing HEAP_ALLOCED from GHC, promising
 faster GC, as long as we can keep the cost of indirections down.

 The relevant wiki article:
 http://ghc.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/HeapAlloced ;
 we are implementing method 2.  The attached patchset is *almost* able to
 support GHC itself; a ghc-stage2 built this way can compile most files,
 but is much slower in some cases, and probably has some correctness bugs.

 Improvements possible:

 * Don't pay for a double indirection when -fPIC is turned on.  Probably
 the easiest way to do this is to *not* bake in the indirections into
 compiled code when it is -fPIC'd, and instead scribble over the GOT.
 However, I don't know how to go backwards from a symbol to a GOT entry, so
 we might need some heinous assembly hacks to get this working.

 * Closure tables should have their indirections short-circuited by the
 initialization code.

 * We are paying an indirection when a GC occurs when the closure is not in
 R1. According to the wiki page, technically this is not needed, but I
 don't know how to eliminate references to the closure itself from
 stg_gc_fun.

 * Properly handle the Windows DLL case (e.g. SRTs); this should be simpler
 now that everything is an indirection.

 * Bikeshed hs_main API changes (because closures are not valid prior to
 RTS initialization, so you have to pass in an indirection instead)

 * Improve static indirection and stable pointer registration, avoiding
 binary bloat from `__attribute(constructor)__` stubs.

 * Need to implement a new megablock tracking structure so we can
 free/check for lost blocks

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8199>
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