Bernd Schmidt <bschm...@redhat.com> writes: > On 03/02/2016 10:53 PM, Vladimir Makarov wrote: >>> 2. update_costs_from_allocno records a cost update not just for the >>> initial allocno, but for each of the visited ones. I can sort of see >>> an argument for doing that (let's say if you assign an allocno in the >>> middle of a copy chain you'd want the tail end of the chain to be >>> reset), but in practice I don't think the present algorithm can work >>> at all. In the case of an allocno in the middle of a copy chain the >>> restore would progress in both directions, and in any case it looks >>> like this approach can end up double-counting things when restoring >>> costs. >>> >> It is just a heuristic. Richard Sandiford proposed this update >> approach. Before it we had only updates of allocnos directly connected >> to allocno in question. Richard's approach helped to improve code in >> some cases. If something works better we should use. The bechmarking >> is the best criterium. > > Ccing Richard in case he has comments.
TBH I don't remember anything about this now. Is it: https://gcc.gnu.org/ml/gcc-patches/2008-09/msg00541.html ? I think that was just tweaking the traversal order in an existing cost update, rather than adding a new one. You might be talking about a different patch though, sorry. Richard
