"specializing a function on a possibly non work-free cast"

[gergoerdi]

With 09c8aa49aa2aa80b638a565c471ab05d853d98be I am getting the following output thousands and thousands of times:

WARNING: Clash.Normalize.Transformations(852): specializing a function on a possibly non work-free cast.
Generated HDL implementation might contain duplicate work.
Please report this as a bug.

Expression where this occurs:

GHC.Integer.Type.plusInteger
  ((Clash.Sized.Internal.Index.fromInteger# @5 5
      0) ▷
    Clash.Sized.Internal.Index.Index8214565720323789241
      5
    ~
    GHC.Integer.Type.Integer3674937295934324780)

Since it doesn't seem to be doing much more than just repeatedly printing this, I don't know if it's worth waiting for it or if it'll just keep looping (and eating up memory).

[gergoerdi]

I don't have a fully standalone way of reproducing this, but I have located that the above error is caused by this part of my code:

data S = MkS
    { timers :: Vec 5 (Unsigned 8)
    }
    deriving (Show, Generic, Undefined)

foo :: State S ()
foo = mapM_ bar [0..4]

bar :: Index 5 -> State S ()
bar i = modify $ \s -> s{ timers = replace i 42 $ timers s }

[gergoerdi]

This workaround seems to work:

foo :: State S ()
foo = mapM_ (bar . fromIntegral) [0..4]

[martijnbastiaan]

@gergoerdi Sorry for the very slow response. I think you can safely ignore the warning, as the expression it warns about is indeed work-free. I'll fix it in a bit.