I implemented -flate-dmd-anal last year Here's some outdated notes about my initial implementation. I share it in order to indicate what thoughts were in my mind at the time (eg re motivation).
https://ghc.haskell.org/trac/ghc/wiki/Frisby2013Q1#LateStrictnessWW Aha! More up-to-date info here, including links to some of the older, motivating tickets. https://ghc.haskell.org/trac/ghc/ticket/7782 https://ghc.haskell.org/trac/ghc/wiki/LateDmd Also, I now suspect this pass is risky: I think it may enter unused arguments. I realize I didn't understand that stuff well enough at the time. This definitely deserves some attention if people are using the flag. To answer your question directly: I do not recall explicitly considering single-entry thunks when implementing -flate-dmd-anal. HTH. On Thu, Oct 30, 2014 at 7:15 AM, Jan Stolarek <jan.stola...@p.lodz.pl> wrote: > I'm resurrecting this 3-month old thread as I have some more questions > about cardinality analysis. > > 1. I'm still a bit confused about terminology. Demand analysis, strictness > analysis, cardinality > analysis - do these three terms mean exactly the same thing? If no, then > what are the > differences? > > 2. First pass of full laziness is followed by floating in. At that stage > we have not yet run the > demand analysis and yet the code that does the floating-in checks whether > a binder is one-shot > (FloatIn.okToFloatInside called by FloatIn.fiExpr AnnLam case). This > suggests that cardinality > analysis is done earlier (but when?) and that demand analysis is not the > same thing as > cardinality analysis. > > 3. Does demand analyser perform any transformations? Or does it only > annotate Core with demand > information that can be used by subsequent passes? > > 4. BasicTypes module defines: > > data OneShotInfo = NoOneShotInfo -- ^ No information > | ProbOneShot -- ^ The lambda is probably applied at > most once > | OneShotLam -- ^ The lambda is applied at most once. > > Do I understand correctly that `NoOneShotInfo` really means no information, > ie. a binding annotated with this might in fact be one shot? If so, then > do we > have means of saying that a binding is certainly not a one-shot binding? > > 5. What is the purpose of SetLevels.lvlMFE function? > > Janek > > > The wiki page just went live: > > > > > https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/Core2CorePipeline > > > > It's not yet perfect but it should be a good start. > > > > > Roughtly, a complete run of the simplifier means "run the simplifier > > > repeatedly until nothing further happens". The iterations are the > > > successive iterations of this loop. Currently there's a (rather > arbitrary) > > > limit of four such iterations before we give up and declare victory. > > > > A limit or a default value for that limit? > > > > To Ilya: > > > If you grep for the "late_dmd_anal" option variable in the > compiler/simplCore/SimplCore.lhs > > > module, you'll see that it triggers a phase close to the endo of > getCoreToDo's tasks, which > > > contains, in particular, the "CoreDoStrictness" pass. This is the > "late" phase. > > > > The paper said that the late pass is run to detect single-entry thunks > and the reason why it is > > run late in the pipeline is that if it were run earlier this information > could be invalidated > > by the transformations. But in the source code I see that this late pass > is followed by the > > simplifier, which can invalidate the information. Also, the > documentation for -flate-dmd-anal > > says: "We found some opportunities for discovering strictness that were > not visible earlier; > > and optimisations like -fspec-constr can create functions with unused > arguments which are > > eliminated by late demand analysis". This says nothing about > single-netry thunks. So, is the > > single-entry thunk optimisation performed by GHC? > > > > Janek > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://www.haskell.org/mailman/listinfo/ghc-devs >
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