On Fri, Jul 23, 2021 at 10:41 AM Kewen.Lin <li...@linux.ibm.com> wrote: > > on 2021/7/22 下午8:56, Richard Biener wrote: > > On Tue, Jul 20, 2021 at 4:37 > > PM Kewen.Lin <li...@linux.ibm.com> wrote: > >> > >> Hi, > >> > >> This v2 has addressed some review comments/suggestions: > >> > >> - Use "!=" instead of "<" in function operator!= (const Iter &rhs) > >> - Add new CTOR loops_list (struct loops *loops, unsigned flags) > >> to support loop hierarchy tree rather than just a function, > >> and adjust to use loops* accordingly. > > > > I actually meant struct loop *, not struct loops * ;) At the point > > we pondered to make loop invariant motion work on single > > loop nests we gave up not only but also because it iterates > > over the loop nest but all the iterators only ever can process > > all loops, not say, all loops inside a specific 'loop' (and > > including that 'loop' if LI_INCLUDE_ROOT). So the > > CTOR would take the 'root' of the loop tree as argument. > > > > I see that doesn't trivially fit how loops_list works, at least > > not for LI_ONLY_INNERMOST. But I guess FROM_INNERMOST > > could be adjusted to do ONLY_INNERMOST as well? > > > > > Thanks for the clarification! I just realized that the previous > version with struct loops* is problematic, all traversal is > still bounded with outer_loop == NULL. I think what you expect > is to respect the given loop_p root boundary. Since we just > record the loops' nums, I think we still need the function* fn?
Would it simplify things if we recorded the actual loop *? There's still the to_visit reserve which needs a bound on the number of loops for efficiency reasons. > So I add one optional argument loop_p root and update the > visiting codes accordingly. Before this change, the previous > visiting uses the outer_loop == NULL as the termination condition, > it perfectly includes the root itself, but with this given root, > we have to use it as the termination condition to avoid to iterate > onto its possible existing next. > > For LI_ONLY_INNERMOST, I was thinking whether we can use the > code like: > > struct loops *fn_loops = loops_for_fn (fn)->larray; > for (i = 0; vec_safe_iterate (fn_loops, i, &aloop); i++) > if (aloop != NULL > && aloop->inner == NULL > && flow_loop_nested_p (tree_root, aloop)) > this->to_visit.quick_push (aloop->num); > > it has the stable bound, but if the given root only has several > child loops, it can be much worse if there are many loops in fn. > It seems impossible to predict the given root loop hierarchy size, > maybe we can still use the original linear searching for the case > loops_for_fn (fn) == root? But since this visiting seems not so > performance critical, I chose to share the code originally used > for FROM_INNERMOST, hope it can have better readability and > maintainability. I was indeed looking for something that has execution/storage bound on the subtree we're interested in. If we pull the CTOR out-of-line we can probably keep the linear search for LI_ONLY_INNERMOST when looking at the whole loop tree. It just seemed to me that we can eventually re-use a single loop tree walker for all orders, just adjusting the places we push. > > Bootstrapped and regtested on powerpc64le-linux-gnu P9, > x86_64-redhat-linux and aarch64-linux-gnu, also > bootstrapped on ppc64le P9 with bootstrap-O3 config. > > Does the attached patch meet what you expect? So yeah, it's probably close to what is sensible. Not sure whether optimizing the loops for the !only_push_innermost_p case is important - if we manage to produce a single walker with conditionals based on 'flags' then IPA-CP should produce optimal clones as well I guess. Richard. > > BR, > Kewen > ----- > gcc/ChangeLog: > > * cfgloop.h (loops_list::loops_list): Add one optional argument root > and adjust accordingly.
