On Wed, Oct 5, 2016 at 3:22 PM, Yuri Rumyantsev <ysrum...@gmail.com> wrote: > Hi All, > > Here is implementation of Richard proposal: > > < For general infrastructure it would be nice to expose a (post-)dominator > < compute for MESE (post-dominators) / SEME (dominators) regions. I believe > < what makes if-conversion expensive is the post-dom compute which happens > < for each loop for the whole function. It shouldn't be very difficult > < to write this, > < sharing as much as possible code with the current DOM code might need > < quite some refactoring though. > > I implemented this proposal by adding calculation of dominance info > for SESE regions and incorporate this change to if conversion pass. > SESE region is built by adding loop pre-header and possibly fake > post-header blocks to loop body. Fake post-header is deleted after > predication completion. > > Bootstrapping and regression testing did not show any new failures. > > Is it OK for trunk?
It's mostly reasonable but I have a few comments. First, re-using bb->dom[] for the dominator info is somewhat fragile but indeed a requirement to make the patch reasonably small. Please, in calculate_dominance_info_for_region, make sure that !dom_info_available_p (dir). You pass loop * everywhere but require ->aux to be set up as an array of BBs forming the region with special BBs at array ends. Please instead pass in a vec<basic_block> which avoids using ->aux and also allows other non-loop-based SESE regions to be used (I couldn't spot anything that relies on this being a loop). Adding a convenience wrapper for loop * would be of course nice, to cover the special pre/post-header code in tree-if-conv.c. In theory a SESE region is fully specified by its entry end exit _edge_, so you might want to see if it's possible to use such a pair of edges to guard the dfs/idom walks to avoid the need to create fake blocks. Btw, instead of using create_empty_bb, unchecked_make_edge, etc. please use split_edge() of the entry/exit edges. Richard. > ChangeLog: > 2016-10-05 Yuri Rumyantsev <ysrum...@gmail.com> > > * dominance.c : Include cfgloop.h for loop recognition. > (dom_info): Add new functions and add boolean argument to recognize > computation for loop region. > (dom_info::dom_info): New function. > (dom_info::calc_dfs_tree): Add boolean argument IN_REGION to not > handle unvisited blocks. > (dom_info::calc_idoms): Likewise. > (compute_dom_fast_query_in_region): New function. > (calculate_dominance_info): Invoke calc_dfs_tree and calc_idoms with > false argument. > (calculate_dominance_info_for_region): New function. > (free_dominance_info_for_region): Likewise. > (verify_dominators): Invoke calc_dfs_tree and calc_idoms with false > argument. > * dominance.h: Add prototype for introduced functions > calculate_dominance_info_for_region and > free_dominance_info_for_region. > tree-if-conv.c: Add to local variables ifc_sese_bbs & fake_postheader. > (build_sese_region): New function. > (if_convertible_loop_p_1): Invoke local version of post-dominators > calculation, free it after basic block predication and delete created > fake post-header block if any. > (tree_if_conversion): Delete call of free_dominance_info for > post-dominators, free ifc_sese_bbs which represents SESE region. > (pass_if_conversion::execute): Delete detection of infinite loops > and fake edges to exit block since post-dominator calculation is > performed per if-converted loop only.
