#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): * The awkwardness of not recording top-level 1* info is that we'd need a demand-analyser flag to tell it whether to do so or not. * I've just realised that this final sweep (dmd anal only) must be just before `CoreTidy`. Reason: currently anyway, `CoreTidy` establishes the exported strictness signatures. We do want to export `f` with a "I use my arg at most once" `1*` annotation. So we want to pin in reliable info just before we freeze it for export, and then not invalidate it. One thing I have longed to do for some time is to get CAF info from the STG form, and combine that CAF info into the `ModIface` bindings. Currently we ''predict'' what it'll be at `CoreTidy`, which is fragile. Maybe the same holds for strictness/usage info. * `OneShot` annotations on lambda binders are a different matter. They say something about the use of the ''function'', not about the use of the binder in the function body. Can a `OneShot` annotation go wrong? Yes if we call that function twice instead of once. But GHC really is pretty paranoid about duplicating arbitrary amounts of work so we are at least much safer here. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11731#comment:24 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler