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Re: A bug in vrp_meet?
On 3/6/19 3:05 AM, Richard Biener wrote:
> On Tue, Mar 5, 2019 at 10:36 PM Jeff Law <law@redhat.com> wrote:
>>
>> On 3/5/19 7:44 AM, Richard Biener wrote:
>>
>>> So fixing it properly with also re-optimize_stmt those stmts so we'd CSE
>>> the MAX_EXPR introduced by folding makes it somewhat ugly.
>>>
>>> Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
>>>
>>> Any ideas how to make it less so? I can split out making optimize_stmt
>>> take a gsi * btw, in case that's a more obvious change and it makes the
>>> patch a little smaller.
>>>
>>> Richard.
>>>
>>> 2019-03-05 Richard Biener <rguenther@suse.de>
>>>
>>> PR tree-optimization/89595
>>> * tree-ssa-dom.c (dom_opt_dom_walker::optimize_stmt): Take
>>> stmt iterator as reference, take boolean output parameter to
>>> indicate whether the stmt was removed and thus the iterator
>>> already advanced.
>>> (dom_opt_dom_walker::before_dom_children): Re-iterate over
>>> stmts created by folding.
>>>
>>> * gcc.dg/torture/pr89595.c: New testcase.
>>>
>>
>> Well, all the real logic changs are in the before_dom_children method.
>> The bits in optimize_stmt are trivial enough to effectively ignore.
>>
>> I don't see a better way to discover and process statements that are
>> created in the bowels of fold_stmt.
>
> I'm not entirely happy so I created the following alternative which
> is a bit larger and slower due to the pre-pass clearing the visited flag
> but is IMHO easier to follow. I guess there's plenty of TLC opportunity
> here but then I also hope to retire the VN parts of DOM in favor
> of the non-iterating RPO-VN code...
>
> So - I'd lean to this variant even though it has the extra loop over stmts,
> would you agree?
>
> Bootstrap / regtest running on x86_64-unknown-linux-gnu.
>
> Richard.
>
> 2019-03-06 Richard Biener <rguenther@suse.de>
>
> PR tree-optimization/89595
> * tree-ssa-dom.c (dom_opt_dom_walker::optimize_stmt): Take
> stmt iterator as reference, take boolean output parameter to
> indicate whether the stmt was removed and thus the iterator
> already advanced.
> (dom_opt_dom_walker::before_dom_children): Re-iterate over
> stmts created by folding.
>
> * gcc.dg/torture/pr89595.c: New testcase.
This one is easier to follow from a logic standpoint. I don't think the
gimple_set_visited bits are going to be terribly expensive in general.
Is that flag in a known state for new statements? I'm guessing it's
cleared by some structure-sized memset as we create the raw statement?
Might be worth clarifying that in the comments in gimple.h.
jeff