Richard, If "fake" exit or entry block is created in dominance how we can determine what is its the only predecessor or successor without using a notion of loop?
2016-10-10 15:00 GMT+03:00 Richard Biener <richard.guent...@gmail.com>: > On Mon, Oct 10, 2016 at 1:42 PM, Yuri Rumyantsev <ysrum...@gmail.com> wrote: >> Thanks Richard for your comments. >> I'd like to answer on your last comment regarding use split_edge() >> instead of creating fake post-header. I started with this splitting >> but it requires to fix-up closed ssa form by creating additional phi >> nodes, so I decided to use only cfg change without updating ssa form. >> Other changes look reasonable and will fix them. > > Ah. In this case can you investigate what it takes to make the entry/exit > edges rather than BBs? That is, introduce those "fakes" only internally > in dominance.c? > >> 2016-10-10 12:52 GMT+03:00 Richard Biener <richard.guent...@gmail.com>: >>> 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.
