On Mon, Mar 4, 2019 at 11:01 PM Qing Zhao <qing.z...@oracle.com> wrote:
>
> Hi, Richard,
>
> > On Mar 4, 2019, at 5:45 AM, Richard Biener <richard.guent...@gmail.com>
> > wrote:
> >>
> >> It looks like DOM fails to visit stmts generated by simplification. Can
> >> you open a bug report with a testcase?
> >>
> >>
> >> The problem is, It took me quite some time in order to come up with a
> >> small and independent testcase for this problem,
> >> a little bit change made the error disappear.
> >>
> >> do you have any suggestion on this? or can you give me some hint on how
> >> to fix this in DOM? then I can try the fix on my side?
> >
> > I remember running into similar issues in the past where I tried to
> > extract temporary nonnull ranges from divisions.
> > I have there
> >
> > @@ -1436,11 +1436,16 @@ dom_opt_dom_walker::before_dom_children
> > m_avail_exprs_stack->pop_to_marker ();
> >
> > edge taken_edge = NULL;
> > - for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
> > - {
> > - evrp_range_analyzer.record_ranges_from_stmt (gsi_stmt (gsi), false);
> > - taken_edge = this->optimize_stmt (bb, gsi);
> > - }
> > + gsi = gsi_start_bb (bb);
> > + if (!gsi_end_p (gsi))
> > + while (1)
> > + {
> > + evrp_range_analyzer.record_def_ranges_from_stmt (gsi_stmt (gsi),
> > false);
> > + taken_edge = this->optimize_stmt (bb, &gsi);
> > + if (gsi_end_p (gsi))
> > + break;
> > + evrp_range_analyzer.record_use_ranges_from_stmt (gsi_stmt (gsi));
> > + }
> >
> > /* Now prepare to process dominated blocks. */
> > record_edge_info (bb);
> >
> > OTOH the issue in your case is that fold emits new stmts before gsi but the
> > above loop will never look at them. See tree-ssa-forwprop.c for code how
> > to deal with this (setting a pass-local flag on stmts visited and walking
> > back
> > to unvisited, newly inserted ones). The fold_stmt interface could in theory
> > also be extended to insert new stmts on a sequence passed to it so the
> > caller would be responsible for inserting them into the IL and could then
> > more easily revisit them (but that's a bigger task).
> >
> > So, does the following help?
>
> Yes, this change fixed the error in my side, now, in the dumped file for pass
> dom3:
>
> ====
> Visiting statement:
> i_49 = _98 > 0 ? k_105 : 0;
> Meeting
> [0, 65535]
> and
> [0, 0]
> to
> [0, 65535]
> Intersecting
> [0, 65535]
> and
> [0, 65535]
> to
> [0, 65535]
> Optimizing statement i_49 = _98 > 0 ? k_105 : 0;
> Replaced 'k_105' with variable '_98'
> gimple_simplified to _152 = MAX_EXPR <_98, 0>;
> i_49 = _152;
Ah, that looks interesting. From this detail we might be
able to derive a testcase as well - a GIMPLE one
eventually because DOM runs quite late. It's also interesting
to see the inefficient code here (the extra copy), probably
some known issue with match-and-simplify, I'd have to check.
> Folded to: i_49 = _152;
> LKUP STMT i_49 = _152
> ==== ASGN i_49 = _152
>
> Visiting statement:
> _152 = MAX_EXPR <_98, 0>;
>
> Visiting statement:
> i_49 = _152;
> Intersecting
> [0, 65535] EQUIVALENCES: { _152 } (1 elements)
> and
> [0, 65535]
> to
> [0, 65535] EQUIVALENCES: { _152 } (1 elements)
> ====
>
> We can clearly see from the above, all the new stmts generated by fold are
> visited now.
We can also see that DOMs optimize_stmt code is not executed on the first stmt
of the folding result (the MAX_EXPR), so the fix can be probably
amended/simplified
with that in mind.
> it is also confirmed that the runtime error caused by this bug was gone with
> this fix.
>
> So, what’s the next step for this issue?
>
> will you commit this fix to gcc9 and gcc8 (we need it in gcc8)?
I'll see to carve out some cycles trying to find a testcase and amend
the fix a bit
and will take care of testing/submitting the fix. Thanks for testing
that it works
for your case.
Richard.
> or I can test this fix on my side and commit it to both gcc9 and gcc8?
>
> thanks.
>
> Qing
>
> >
> > Index: gcc/tree-ssa-dom.c
> > ===================================================================
> > --- gcc/tree-ssa-dom.c (revision 269361)
> > +++ gcc/tree-ssa-dom.c (working copy)
> > @@ -1482,8 +1482,25 @@ dom_opt_dom_walker::before_dom_children
> > edge taken_edge = NULL;
> > for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
> > {
> > + gimple_stmt_iterator pgsi = gsi;
> > + gsi_prev (&pgsi);
> > evrp_range_analyzer.record_ranges_from_stmt (gsi_stmt (gsi), false);
> > taken_edge = this->optimize_stmt (bb, gsi);
> > + gimple_stmt_iterator npgsi = gsi;
> > + gsi_prev (&npgsi);
> > + /* Walk new stmts eventually inserted by DOM. gsi_stmt (gsi) itself
> > + while it may be changed should not have gotten a new definition.
> > */
> > + if (gsi_stmt (pgsi) != gsi_stmt (npgsi))
> > + do
> > + {
> > + if (gsi_end_p (pgsi))
> > + pgsi = gsi_start_bb (bb);
> > + else
> > + gsi_next (&pgsi);
> > + evrp_range_analyzer.record_ranges_from_stmt (gsi_stmt (pgsi),
> > + false);
> > + }
> > + while (gsi_stmt (pgsi) != gsi_stmt (gsi));
> > }
> >
> > /* Now prepare to process dominated blocks. */
> >
> >
> > Richard.
> >
> >> Thanks a lot.
> >>
> >> Qing
> >>
> >>
> >>
> >> Richard.
> >>
> >>
>
