[GHC] #15960: Using -g causes differences in generated core.

[GHC]

#15960: Using -g causes differences in generated core.
-------------------------------------+-------------------------------------
           Reporter:  AndreasK       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.3
          Component:  Compiler       |           Version:  8.6.2
           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:
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 For nofib/shootout/fannkuch-redux:

 Normal results
 {{{
 > /e/ghc-8.6.1/bin/ghc.exe Main.hs -O2 -XBangPatterns -fforce-recomp
 -ddump-simpl -dsuppress-all -dsuppress-uniques | less
 ...
 Result size of Tidy Core
   = {terms: 2,747, types: 2,736, coercions: 100, joins: 50/73}
 ...
 }}}

 {{{
 > /e/ghc-8.6.1/bin/ghc.exe Main.hs -O2 -XBangPatterns -fforce-recomp
 -ddump-simpl -dsuppress-all -dsuppress-uniques -g | less
 ...
 Result size of Tidy Core
   = {terms: 2,654, types: 2,557, coercions: 100, joins: 38/71}
 ...
 }}}

 There are also structural differences in the generated code.

 I've hit the issue with a tree based on head as well so likely happening
 there as well.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15960>
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