Hello, > >> > quite a lot at the moment). To keep the information valid, we need > >> > to prevent optimizations from destroying it (e.g., if the number > >> > is n_1 = n_2 - 1, and this is the last use of n_1, we do not want > >> > DCE to remove it); this is easy to achieve if n_1 would be the > >> > argument of LOOP_HEADER. > > You are proposing to complete the ssa representation such that > foreach_ssa_uses also iterates over the niter information (a bit like vrp > modifies the ssa chains with its extra assert information). Wouldn't it > be possible to not insert this niter information in the representation of > the > program (ie. not inserting a new tree node) but just modify the ssa > iterators > to also return the expressions that we store on the side?
yes, it would be possible, however, possibly quite error-prone. > >> > Without this tree node in IL, we would need > >> > to handle this specially in DCE, and possibly also other optimizers. > > What are the other transformations that remove definitions that are not > used? ivopts remove bivs that they replace, and I suspect that vectorizer does something similar as well. I do not know about other optimizers. Zdenek
