#13160: Simplify CoreFV.FVAnn -------------------------------------+------------------------------------- Reporter: simonpj | Owner: bgamari Type: task | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3170 Wiki Page: | -------------------------------------+------------------------------------- Description changed by mpickering: Old description:
When introducing type-in-type, Richard elaborated the free varaible finder so that it finds three things at once (in `CoreFV`): {{{ data FVAnn = FVAnn { fva_fvs :: DVarSet -- free in expression , fva_ty_fvs :: DVarSet -- free only in expression's type , fva_ty :: Type -- expression's type } }}} I think `fva_ty` is needed only to support `fva_ty_fvs`. And `fva_ty_fvs` seems to be used only to support the calls to `freeVarsOfType` in `FloatIn`. And those calls in turn are only to suppor `used_in_ty` in `FloatIn.sepBindsByDropPoint`.
In conversation yesterday, Richard and I agreed that all this is unnecessary. Coercion bindings simply do not float inwards, so we do not need to take these precautions. (We should add a Note to explain why they don't float, and what problem might arise if they did.)
To confirm this I set `used_in_ty` to `False` and compiled from scratch; everything is fine.
So I propose that we
* get rid of the `ty_fvs` argument to `sepBindsByDropPoint` * simplfy `FVAnn` to just gather free variables (ie one field only)
Result: it's all simpler.
Richard will do this when he gets a moment. But I really hope for 8.2
New description: When introducing type-in-type, Richard elaborated the free variable finder so that it finds three things at once (in `CoreFV`): {{{ data FVAnn = FVAnn { fva_fvs :: DVarSet -- free in expression , fva_ty_fvs :: DVarSet -- free only in expression's type , fva_ty :: Type -- expression's type } }}} I think `fva_ty` is needed only to support `fva_ty_fvs`. And `fva_ty_fvs` seems to be used only to support the calls to `freeVarsOfType` in `FloatIn`. And those calls in turn are only to suppor `used_in_ty` in `FloatIn.sepBindsByDropPoint`. In conversation yesterday, Richard and I agreed that all this is unnecessary. Coercion bindings simply do not float inwards, so we do not need to take these precautions. (We should add a Note to explain why they don't float, and what problem might arise if they did.) To confirm this I set `used_in_ty` to `False` and compiled from scratch; everything is fine. So I propose that we * get rid of the `ty_fvs` argument to `sepBindsByDropPoint` * simplfy `FVAnn` to just gather free variables (ie one field only) Result: it's all simpler. Richard will do this when he gets a moment. But I really hope for 8.2 -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13160#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler