Hi, Am Dienstag, den 31.12.2013, 11:33 +0000 schrieb Simon Peyton-Jones:
Interesting. We can discuss when you get back, but let me jot down one comment. You write:
| This will always happen if the join point function gets a richer | CPR property than the function that it belongs to
Good observation. Maybe we can exploit it directly rather than figuring out "common contexts"? If we knew, for each local function, whether it was a join point, and if so for what, we could just make its inferred CPR property no richer than its "parent", perhaps.
correct, I thought about this as well. It could be a post-processing step, after demand analysis, but before worker-wrapper, that goes through the file and reduces CPR information where it is found to be non-helpful. There is also a related issue with CPR’ing a function whose call is used in a argument position: let f x = ... -- in ... g (f z) ... When is CPR’ing f useful? Only if g will get w/w’ed in a way that cancels with the CPR wrapper of f. And when is that the case? If the demand of g on its first argument is as least as rich as f CPR’s wrapper. Again, if f’s CPR information is richer than g’s demand CPR is not useful. It seems that a generalization of the idea „fix CPR information to be no richer than useful“ will need some kind of demand information on arguments. (In this case, doing CPR of f and then Common Context will clean up any useless unwrapping, if all uses of f have the same problem.) Greetings from Karlsruhe, Joachim -- Joachim “nomeata” Breitner mail@joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata@joachim-breitner.de • GPG-Key: 0x4743206C Debian Developer: nomeata@debian.org