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

[GHC]

#8834: 64-bit windows cabal.exe segfaults in GC
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        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:
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Comment (by jstolarek):

 awson, great bisecting job here!

 The intention behind the faulty commit is that both older and newer
 implementations are semantically identical (which turns out not to be the
 case) but the newer one avoids code duplication.

 > I think your analysis is right, that it is the change to okToInline that
 is at fault.

 Two other possibilities include:

 1. `conflict` function
 2. instance definition for `GlobalReg` datatype in
 [[GhcFile(compiler/cmm/CmmNode.hs)]] in the `DefinerOfRegs`. That's the
 place were we say what global registers are defined (and therefore
 clobbered) by each Cmm node.

 awson, to pin this bug we have to know the difference between correct and
 incorrect Cmm. Could you compile your minimal example with GHC HEAD (which
 will give us the segfaulting Cmm) and with your patched version (which
 will give us working Cmm) and upload them here? Dump the Cmm with `-ddump-
 cmm` flag. I see that you're calling `print` in your example. My
 experience is that it adds a lot of extra Cmm to analyse. Could you see if
 splitting your code into two modules also causes the bug:

 {{{
 module T8834 where

 import qualified Data.ByteString.Char8 as BSS

 T8834 :: IO Int
 T8834 = do
   cache <- BSS.readFile "00-index.cache"
   return (length $ BSS.lines cache)
 }}}

 {{{
 module Main where

 import T8834

 main :: IO ()
 main = T8834 >>= print
 }}}

 If this also causes the bug then most likely we only need Cmm dump for
 `T8834` module.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8834#comment:10>
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