Semantically-equivalent expressions evaluating at different values with -O1

The following code shows inconsistent results when compiled with -O1:

import Data.Bits ((.&.))

flags :: Int -> [Int]
flags x = filter (\y -> x .&. y > 0) [1, 128, 129, 255]

main :: IO ()
main = do
  putStrLn $ show $ flags $ 255   -- These lines should display
  putStrLn  (show  (flags   255)) -- the same value, right?

-- It appears that this is related to something that started
-- with GHC 7.10, but was also changed in GHC 8.0, as we can
-- see from the following tests:
--
-- Stack snapshot lts-0.7 (GHC 7.8.3), with -O2
-- [1,128,129,255]
-- [1,128,129,255]
--
-- Stack snapshot lts-2.22 (GHC 7.8.4) with -O2
-- [1,128,129,255]
-- [1,128,129,255]
--
-- Stack snapshot lts-3.22 (GHC 7.10.2) with -O2
-- [1]
-- [1]
--
-- Stack snapshot lts-6.30 (GHC 7.10.3) with -O2
-- [1]
-- [1]
--
-- Stack snapshot lts-7.20 (GHC 8.0.1) with -O2
-- [1]
-- [1,128,129,255]
--
-- Stack snapshot lts-8.5 (GHC 8.0.2) with -O2
-- [1]
-- [1,128,129,255]
--
-- In GHC 8.0.2, compiling with any of the following...
--   -O0
--   -O2 -fno-cmm-sink
--   -O2 -fno-enable-rewrite-rules
--
-- ...we get the expected results:
-- [1,128,129,255]
-- [1,128,129,255]
--
-- Using only -O1, we get the abnormal behavior again:
-- [1]
-- [1,128,129,255]

Trac metadata

Trac field	Value
Version	8.0.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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