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.


> 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.

Reply via email to