[GHC] #14997: mut_list_size calculation is off

[GHC]

#14997: mut_list_size calculation is off
-------------------------------------+-------------------------------------
           Reporter:  osa1           |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  lowest         |         Milestone:
          Component:  Runtime        |           Version:  8.5
  System                             |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Program:

 {{{
 main = print (foldr (+) 0 [ 0 .. 10000 ] :: Int)
 }}}

 Compile:

 {{{
 $ ghc-stage2 Main.hs -debug -rtsopts -O0
 }}}

 Run:

 {{{
 $ ./Main +RTS -Dg
 }}}

 It prints something like

 {{{
 mut_list_size: 16 (0 vars, 0 arrays, 0 MVARs, 0 TVARs, 0
 TVAR_WATCH_QUEUEs, 0 TREC_CHUNKs, 0 TREC_HEADERs, 0 ATOMIC_INVARIANTs, 0
 INVARIANT_CHECK_QUEUEs, 0 others)
 }}}

 So there are two objects in the mut list, but `scavenge_mutable_list`
 wasn't able to find anything. This is curious, and it seems like a bug.

 Pretty much any program has this bug, `mut_list_size` and sum of objects
 found in the mut list never match.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14997>
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