[GHC] #4012: Compilation results are not deterministic

[GHC]

#4012: Compilation results are not deterministic
-------------------------------------+-------------------------------------
        Reporter:  kili              |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  high              |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  6.12.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Other             |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------

Comment (by thoughtpolice):

 Yes. I removed `shortOutIndirections` in `SimplCore`:

 {{{
 diff --git a/compiler/simplCore/SimplCore.hs
 b/compiler/simplCore/SimplCore.hs
 index 0a2f8e4..95c5cce 100644
 --- a/compiler/simplCore/SimplCore.hs
 +++ b/compiler/simplCore/SimplCore.hs
 @@ -667,7 +667,7 @@ simplifyPgmIO pass@(CoreDoSimplify max_iterations
 mode)
                  --
                  -- ToDo: alas, this means that indirection-shorting does
 not happen at all
                  --       if the simplifier does nothing (not common, I
 know, but unsavoury)
 -           let { binds2 = {-# SCC "ZapInd" #-} shortOutIndirections
 binds1 } ;
 +           let { binds2 = {-# SCC "ZapInd" #-} if True then binds1 else
 shortOutIndirections binds1 } ;

                  -- Dump the result of this iteration
             dump_end_iteration dflags print_unqual iteration_no counts1
 binds2 rules1 ;
 }}}

 Then I compiled the test in comment:76 with `-fno-cse` and observed the
 ABI difference went away. So killing CSE may get us a long way for NixOS

 I admit I tested this on GHC 7.10, and not the HEAD branch. Brian, you
 couldn't reproduce this on HEAD at all? I can double check this, but that
 somewhat surprises (and worries!) me.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4012#comment:98>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler