#11731: Simplifier: Inlining trivial let can lose sharing -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.1 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:D2064 Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Let's be careful to distinguish three kinds of `IdInfo`, all pinned on an `Id`: * `demandInfo`: says how the `Id` is used (demanded) by its scope. * `strictnessInfo`: describes the demand transformer for the `Id`; it tnansforms a demand on the `Id` to a demand on its arguments and free variables. * `oneShotInfo`: for lambda-bound `Id`s only, says whether the function is called at most once. (It says nothing about how the `Id` is used in the body of the lambda.) I think we have decided (#11770) that * only the demand analyser sets `demandInfo` and `strictnessInfo` * only the occurrence analyser sets `oneShotInfo`. The `demandInfo` on an `Id` includes `1*` usage info, which is fragile so perhaps we should erase it. The `strictnessInfo` on an `Id` also contains `1*` usage info, e.g about the function arguments. That too is fragile to transformations of the function body, so perhaps we should erase it too. I've just realised that a convenient place to erase it might be the worker/wrapper pass. So then we'd have * the demand analyser sets `demandInfo` and `strictnessInfo` * the worker-wrapper pass erases 1* info from `demandInfo` and `strictnessInfo` * the occurrence analyser sets `oneShotInfo` -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11731#comment:26 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler