[GHC] #15519: Minor code refactoring leads to drastic performance degradation

[GHC]

#15519: Minor code refactoring leads to drastic performance degradation
-------------------------------------+-------------------------------------
        Reporter:  danilo2           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 How can I demonstrate without Criterion?  (trying to install criterion
 with my in-place HEAD compiler leads to a raft of dependency conflicts
 that I do not understand.)

 I tried just running `test0 src1`, `test1 src1`, `test2 src1` but they all
 behaved identically.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15519#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler