OK, I think I didn't give enough explanation in my last mail. My understanding is that entry block of the graph will be initialized with a fact (Const M.empty), while every other node will be initialized with Bottom. Now, when I reach a block that is first block in a loop it will have more than one predecessor (let's assume that it has two). One predecessor will have fact (Const ...) propagated from the entry node, but the other one will not be analyzed yet and therefore should be Bottom. That's why I think it should be picked up by first equation of joinCpFacts. Later on, when we reach end of a loop we will propagate (Const ...) to the entry block of a loop and only then we will be joining two (Const ...) facts - that's when second equation of joinCpFacts should come in to play.
Janek
----- Oryginalna wiadomość -----
Od: "Jan Stolarek"
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