[GHC] #8834: 64-bit windows cabal.exe segfaults in GC

[GHC]

#8834: 64-bit windows cabal.exe segfaults in GC
----------------------------------+----------------------------------
        Reporter:  awson          |            Owner:
            Type:  bug            |           Status:  patch
        Priority:  highest        |        Milestone:  7.8.1
       Component:  Compiler       |          Version:  7.8.1-rc2
      Resolution:                 |         Keywords:
Operating System:  Windows        |     Architecture:  x86_64 (amd64)
 Type of failure:  Runtime crash  |       Difficulty:  Unknown
       Test Case:                 |       Blocked By:
        Blocking:                 |  Related Tickets:
----------------------------------+----------------------------------

Comment (by awson):

 I've inspected "bad" Cmm a bit and found
 [https://ghc.haskell.org/trac/ghc/attachment/ticket/8834/lines1_bad#L2276
 this]:
 {{{
            call (stg_gc_fun)(R1) args: 40, res: 0, upd: 8;
        c2gF:
            if (%MO_S_Le_W64(R5, 0)) goto c2gB; else goto c2gC;
 }}}
 `R5` is `r8` and is volatile on Win64. I don't see it restored before
 `%MO_S_Le_W64(R5, 0)` (honestly, I don't know what `%MO_S_Le_W64(R5, 0)`
 is).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8834#comment:41>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler