[GHC] #15114: ghc 8.4.1 optimizes True to False

2 May 2018

      #15114: ghc 8.4.1 optimizes True to False
-------------------------------------+-------------------------------------
           Reporter:  elaforge       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Compiler       |           Version:  8.4.1
           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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 Ok, here's a short module:

 {{{#!hs
 import qualified Control.Exception as Exception

 main :: IO ()
 main = do
     unserialize
     putStrLn "all is well"

 unserialize :: IO Char
 unserialize =
     if definitelyTrue
         then do
             return 'a'
         else do
             Exception.evaluate (error "wrong place")

 {-# NOINLINE definitelyTrue #-}
 definitelyTrue :: Bool
 definitelyTrue = True
 }}}

 When compiled with -O on 8.4.1, this should print "wrong place".
 Without -O, or with 8.4.2, or if True can be inlined, or without
 evaluate, all is well.  I can reproduce this on OS X 10.13.4.

 This could be related to a known bug with Exception.evaluate in 8.4.1:
 #3930

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15114
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