#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 nomeata):
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.
Not too awkward, there is `AnalEnv` that can hold on to it. But alternatively, we could do a second sweep that goes through the AST after DmdAnal and remove the bits we want removed. This would allow the demand analyzer to set and make use of `1*` internally, e.g. during fixed- point iteration and such. This pass would also allow us to set the `OneShot` annotations on lambda binders based on the demand on the function, before we remove it – the occurrence analyzer cannot do it for us any more. Or we move the onus of removing invalidated demand signatures onto the pass that actually invalidates them, and just be much more aggressive about this. The occurrence analyzer (if we think of it as the first thing done by the simplifier) would be a natural choice, with the added benefit that it can still use the information to set `OneShot` information before zapping it.
Can a `OneShot` annotation go wrong?
I cannot construct an example out of my head that would still work if we eradicated thanks that are wrongly marked as single entry, so we might be safe. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11731#comment:25 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler