So if I understand correctly, OtherCon is only created here: https://gitlab.haskell.org/ghc/ghc/-/blob/a952dd80d40bf6b67194a44ff71d7bf759... simplAlt env _ imposs_deflt_cons case_bndr' cont' (Alt DEFAULT bndrs rhs) = assert (null bndrs) $ do { let env' = addBinderUnfolding env case_bndr' (mkOtherCon imposs_deflt_cons) -- Record the constructors that the case-binder *can't* be. ; rhs' <- simplExprC env' rhs cont' ; return (Alt DEFAULT [] rhs') } What you should know is that in Core case-expressions are actually more like: case scrut as b of alts where `b` binds the evaluated result of `scrut. So if I am to understand the `simplAlt` code correctly, `case_bndr'` is the binder for the evaluated result of `scrut`. And what is recorded in the unfolding is that once we get to the DEFAULT pattern, we know that `case_bndr'` cannot be the constructors in `imposs_deflt_cons` (probably the constructor matched by the other alternatives). Now... there's also a FloutOut pass, which might have floated that `case_bndr'` to the TopLevel. And I think that is what you're seeing, and I think you can simply ignore them. Also... another thing that you should know is that -fexpose-all-unfoldings doesn't actually expose *all* unfoldings. Bottoming bindings are never exposed. That's why in the Clash compiler we have the following code when loading core-expressions from .hi files https://github.com/clash-lang/clash-compiler/blob/cb93b418865e244da50e1d2bc8... loadExprFromTyThing :: CoreSyn.CoreBndr -> GHC.TyThing -> Maybe CoreSyn.CoreExpr loadExprFromTyThing bndr tyThing = case tyThing of GHC.AnId _id | Var.isId _id -> let _idInfo = Var.idInfo _id unfolding = IdInfo.unfoldingInfo _idInfo in case unfolding of CoreSyn.CoreUnfolding {} -> Just (CoreSyn.unfoldingTemplate unfolding) CoreSyn.DFunUnfolding dfbndrs dc es -> Just (MkCore.mkCoreLams dfbndrs (MkCore.mkCoreConApps dc es)) CoreSyn.NoUnfolding #if MIN_VERSION_ghc(9,0,0) | Demand.isDeadEndSig $ IdInfo.strictnessInfo _idInfo #else | Demand.isBottomingSig $ IdInfo.strictnessInfo _idInfo #endif -> do let noUnfoldingErr = "no_unfolding " ++ showPpr unsafeGlobalDynFlags bndr Just (MkCore.mkAbsentErrorApp (Var.varType _id) noUnfoldingErr) _ -> Nothing _ -> Nothing i.e. when we encounter a NoUnfolding with a bottoming demand signature, we conjure an absentError out of thin air. On Fri, 1 Apr 2022 at 10:05, ÉRDI Gergő <gergo@erdi.hu> wrote:
Hi,
I'm CC-ing the Clash mailing list because I believe they should have encountered the same problem (and perhaps have found a solution to it already!).
I'm trying to use `.hi` files compiled with `ExposeAllUnfoldings` set to reconstruct full Core bindings for further processing. By and large, this works, but I get tripped up on identifiers whose unfolding is only given as `OtherCon []`. It is unclear to me what is causing this -- some of them are recursive bindings while others are not.
The problem, of course, is that if all I know about an identifier is that it is `OtherCon []`, that doesn't allow me to restore its definition. So is there a way to tell GHC to put "full" unfoldings everywhere in `ExposeAllUnfoldings` mode?
Thanks, Gergo
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