Two Hoopl questions

Jan Stolarek jan.stolarek at
Wed Jul 31 18:44:46 CEST 2013

Does Hoopl handle Bottom internally? By "Bottom" I mean the loop-breaking thing that means "this predecessor does not execute". From the debugging output I added to my code it looks that it in fact does because it doesn't do a join when first analyzing a block with two predecessors. If this is really the case then what is the purpose of defining bottom in DataflowLattice?


----- Oryginalna wiadomość -----
Od: "Edward Z. Yang" <ezyang at MIT.EDU>
Do: "Jan Stolarek" <jan.stolarek at>
DW: "Simon Peyton-Jones" <simonpj at>, "ghc-devs" <ghc-devs at>
Wysłane: wtorek, 30 lipiec 2013 20:40:53
Temat: Re: Two Hoopl questions

What happens when you put a loop in your code?


Excerpts from Jan Stolarek's message of Tue Jul 30 08:34:44 -0700 2013:
> I'll allow myself to ask my second question again:
> 2) In my algorithm I need to initialize all of the blocks in a graph with bottom element of a lattice, except for the entry block, which needs some other initial values. I've written something like this:
> cmmCopyPropagation dflags graph = do
>     let entry_blk = g_entry graph
>     g' <- dataflowPassFwd graph [(entry_blk, (Top, Top))] $
>             analRewFwd cpLattice cpTransfer cpRewrite
>     return . fst $ g'
> cpLattice = DataflowLattice "copy propagation" (Bottom, Bottom) cpJoin
> However, it seems that Bottom values passed to cpLattice are ignored - I could replace second parameter to DataflowLattice with `undefined` and the code would still run without causing an error. Is there something obviously wrong in the way I pass initial fact values to dataflowPassFwd, or should I look for the problem in other parts of my code?
> Janek

More information about the ghc-devs mailing list