With foo.hs:

main = print (4, "foo")

Compile it and run it like:

% ghc-stage2 -O -g foo.hs
% ./foo
(4,"\CANq@")

Note that the content of the string literal is broken, although the length is preserved.

With -dcore-lint, the following error is produced:

*** Core Lint errors : in result of Simplifier ***
<no location info>: warning:
    [RHS of ww2_s3hG :: Addr#]
    Recursive or top-level binder has strict demand info: ww2_s3hG
    Binder's demand info: <L,U>

The offending binding is:

ww2_s3hG :: Addr#
[LclId,
 Unf=Unf{Src=<vanilla>, TopLvl=False, Value=True, ConLike=True,
         WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 20 0}]
ww2_s3hG = src<foo.hs:1:18-22> "foo"#

Happens with ghc 8.4.1-rc1 and with HEAD (df2c3b33).