Hello GHC Devs,

First some context:

I'm using the GHC API to convert Haskell to digital circuit descriptions (clash compiler).

When viewed as a structural description of a circuit, recursive let-bindings can be turned into feedback loops.

In general, when viewed as a structural description of a circuit, recursive functions describe infinite hierarchy, i.e. they are not realisable as circuit.

So now my problem: the simplifier turns recursive let-bindings to recursive functions; i.e. it is turning something which I can translate to a circuit to something which I cannot translate to a circuit.

Next follows a reduced test case which exemplifies this behaviour:

```

import Control.Applicative

topEntity :: [((),())]

topEntity = (,) <$> outport1 <*> outport2

where

(outport1, outResp1) = gpio (decodeReq 1 req)

(outport2, outResp2) = gpio (decodeReq 2 req)

ramResp = ram (decodeReq 0 req)

req = core $ (<|>) <$> ramResp <*> ((<|>) <$> outResp1 <*> outResp2)

{-# INLINE req #-}

core :: [Maybe ()] -> [()]

core = fmap (maybe () id)

{-# NOINLINE core #-}

ram :: [()] -> [Maybe ()]

ram = fmap pure

{-# NOINLINE ram #-}

decodeReq :: Integer -> [()] -> [()]

decodeReq 0 = fmap (const ())

decodeReq 1 = id

decodeReq _ = fmap id

{-# NOINLINE decodeReq #-}

gpio :: [()] -> ([()],[Maybe ()])

gpio i = (i,pure <$> i)

{-# NOINLINE gpio #-}

```

Now, when we look at the output of the desugarer (-ddump-ds), we can see that the core-level binder of `topEntity` basically follows the Haskell code.

However, when we look at the simplifier output, with nearly all transformations disabled (-O0 -ddump-ds), you will see that parts of `topEntity` are split into 3 different top-level, mutually recursive, functions.

So my question are:

- Which part of the simplifier is turning these local recursive let-binders into global recursive functions?

- Is there some way to disable this transformation?

- If not, how much effort do you think it would be to put this behaviour behind a dynflag? So that I, as a GHC API user, can disable it for my use-case. I'm willing to implements this dynflag myself.

Kind regards,

Christiaan