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Re: A bug in vrp_meet?
On Tue, Mar 19, 2019 at 8:53 PM Jeff Law <law@redhat.com> wrote:
>
> 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?
Yes, it's of course not documented that way but IMHo the only reasonable
state.
> Might be worth clarifying that in the comments in gimple.h.
>
> jeff
>