Re: [GHC] #13916: Optimizations create run time seg faults

15 Jul 2017

      #13916: Optimizations create run time seg faults
-------------------------------------+-------------------------------------
        Reporter:  newthin           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.2
       Component:  Compiler          |              Version:  8.0.2
  (CodeGen)                          |
      Resolution:                    |             Keywords:  optimization
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Runtime crash     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 Here is a sketch of the structure of `takeEnv` along with strictness
 signatures,
 {{{
 takeEnv =
   \ (@ env_a3hT)
     (x_X3Lx [Dmd=<B,1*U(U,U,U)>] :: Vector (TMVar env_a3hT))
     (eta_B1 [Dmd=<B,U>] :: GHC.Prim.State# GHC.Prim.RealWorld) ->
   case x_X3Lx of
       { Data.Vector.Vector ipv_s4Q7 [Dmd=<B,U>] ipv_s4Q8 [Dmd=<B,U>]
                            ipv_s4Q9 [Dmd=<B,U>] ->
         joinrec {
           foldlM_loop_a45q [Occ=LoopBreaker]
             :: GHC.Types.SPEC
                -> STM env_a3hT
                -> Int
                -> (# GHC.Prim.State# GHC.Prim.RealWorld, env_a3hT #)
           foldlM_loop_a45q (ds4_a45s [Dmd=<S,1*U>] :: GHC.Types.SPEC)
                            (z1_a45t [Dmd=<C(S),1*C1(U(U,U))>] :: STM
 env_a3hT)
                            (s1_a45u [Dmd=<S(S),1*U(U)>] :: Int) = ...
         }
         in jump foldlM_loop_a45q
              GHC.Types.SPEC
              (((src<Bracket.hs:119:32-36> GHC.Prim.retry#) @ env_a3hT)
               `cast` (Sym (GHC.Conc.Sync.N:STM[0] <env_a3hT>_R)
                       :: ((GHC.Prim.State# GHC.Prim.RealWorld
                            -> (# GHC.Prim.State# GHC.Prim.RealWorld,
 env_a3hT #)) :: *)
                          ~R#
                          (STM env_a3hT :: *)))
              (GHC.Types.I# 0#)
       }
 }}}

 Note how the analyzer somehow concludes hyperstrict demands for all of the
 binders bound by the case analysis of the `Vector` despite the fact that
 the whole thing consists of nothing more than a call to `foldlM_loop_a45q`
 which does not itself diverge.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13916#comment:17>
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