On 26/08/13 10:00, Jan Stolarek wrote:
1. This adds a new constraint on the dataflow algorithm, namely that it
must traverse the blocks in the correct order.
I don't follow. From what I've seen in the code Hoopl orders blocks using
depth-first traversal.
For backwards analysis it reverses that order. I don't think that proposed
changes will affect
this. What did I miss?
You didn't miss anything. The new constraint is that forwards analysis
*must* process blocks in this order, whereas previously it didn't have to.
2. Has anyone tried implementing this change? I'm slightly concerned
that having a difference between forward and backward analyses might
lead to divergence in some of the shared parts of the internals of the
algorithm.
If it turns out that forward and backward cases have to diverge to implement
this change, will
that be acceptable? GHC's specialized Hoopl module
(compiler/cmm/Hoopl/Dataflow) already has
separate functions for handling forward and backward analysis.
But they share the core fixpoint algorithm underneath: fixpoint,
fixpointAnal, and some auxiliary functions. It's not a big deal. This
code is heavily tuned though, so keep an eye on performance.
Cheers,
Simon
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