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

[GHC]

#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
      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:                    |
-------------------------------------+-------------------------------------
Description changed by adamse:

Old description:

> 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

New description:

 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:
 #13930

--

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15114#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler