I was looking to see what needs to be done to un-stick this previously
submitted patch:
http://gcc.gnu.org/ml/gcc-patches/2012-05/msg01419.html
Paolo's suggestion was to re-write this to use a "tortoise-and-hare"
algorithm to detect the circularity, rather than Andrew's solution of
using a pointer_set to keep track of already-visited states.
Having spent a couple hours scratching my head over how to do the
suggested re-write, I'm thinking that Andrew's proposed patch is really
the better solution after all. This isn't a linked list we're
traversing, it's an iterative computation, so doing the
tortoise-and-hare thing either requires a lot of extra recomputation
even in the normal case where it terminates quickly, or building some
data structures to track already-visited states. And, if we're going to
build data structures, why not use ones we already have a convenient
library for? What else are such libraries for but to consolidate common
code and make it easier to express such idioms? IMO, that's a
lighter-weight solution than further complicating this code, and I feel
much more confident that it'll squash an entire class of lurking bugs
without introducing new ones.
Paolo, will you reconsider this? Anyone else care to join the fray?
-Sandra
