On Mon, Oct 10, 2016 at 4:17 PM, Yuri Rumyantsev <ysrum...@gmail.com> wrote: > 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?
The caller passes in an entry and exit edge instead of a block or loop. Richard. > 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.
