#9718: Avoid TidyPgm predicting what CorePrep will do -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: CodeGen, CAFs Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by osa1): I started working on this. A few notes: - We want to be able to change CAFFY-ness and arity information not only in Core, but also in STG. #15038 happened because CAFFY-ness was changed in STG. In Phab:D4717 (for #15113) we change CAFs in CoreToStg. - I think to update an iface file after STG we could update the old `ModIface` (used to generate the initial file) and pass it to `hscMaybeWriteIface` when we're done with transformations (right before starting to generate Cmm). So the only extra thing we keep in memory would be the `ModIface`. Alternatively I think we could implement a `ModIfaceUpdate` type that represents changes in `Name`s in an existing interface file. Then `updateIface` function would read the iface file, apply the updates to the in-memory representation, then write it again. This trades performance for residency (although peak memory may stay the same). - `ModIface` is currently not suitable for updates. The field that holds iface definitions has type `[(Fingerprint,IfaceDecl)]`, which is hard to update (need to search the entire list to find the `IfaceDecl` for a given `Name`. - Similarly, id details of a `IfaceDecls` is also hard to update. The relevant types are: {{{ data IfaceIdInfo = NoInfo -- When writing interface file without -O | HasInfo [IfaceInfoItem] -- Has info, and here it is data IfaceInfoItem = HsArity Arity | HsStrictness StrictSig | HsInline InlinePragma | HsUnfold Bool -- True <=> isStrongLoopBreaker is true IfaceUnfolding -- See Note [Expose recursive functions] | HsNoCafRefs | HsLevity -- Present <=> never levity polymorphic }}} So to update caf refs we need to filter the whole list. To update the arity we need to drop any existing `HsArity` info items and cons a new one. Depending on how large these lists are perhaps this isn't as big of a problem as the previous item though. - I'm assuming that `idName` of a top-level STG binder is the `Name` used in `IfaceDecl` for the declaration, so we don't need to generate a map from STG binders to `IfaceDecl` names. In my testing I found this to be true, but I only tried tiny programs so far. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9718#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler