RFR(XS): 8027626: assert(Opcode() != Op_If || outcnt() == 2) failed: bad if #1

[Krystal Mok]

Hi Roland,

Thanks for the reply! I'll try to understand the issue and see if I can get
a simplified test case.

- Kris

On Tue, Jan 6, 2015 at 5:40 AM, Roland Westrelin <
roland.westrelin at oracle.com> wrote:

> Hi Kris,
>
> > Do you have a regression test case that can show the bug and show the
> fix works?
>
> I don’t have a simple test case. For the bug to appear, the IGVN needs to
> process the nodes in a specific order. I don’t see how to get it to do that
> with a simple test case.
>
> Roland.
>
> > I noticed the replay file in the bug report, but a runnable test case
> (not just replaying) would give me a better sense. Thanks!
> >
> > Best regards,
> > Kris
> >
> > On Mon, Jan 5, 2015 at 1:33 PM, Roland Westrelin <
> roland.westrelin at oracle.com> wrote:
> > Hi Vladimir,
> >
> > Thanks for looking at this.
> >
> > > I think correct fix will be eager dead 12212 If node elimination when
> 12214 is replaced by 18733. Keep it connected to graph can cause problems
> in other places.
> >
> > IfFalseNode::Identity() is what optimizes 12212/12214 out. Should I make
> it an Ideal transformation so that I can call igvn->remove_dead_node() on
> the dead branch?
> >
> > Roland.
> >
> > >
> > > Thanks,
> > > Vladimir
> > >
> > > On 1/5/15 7:48 AM, Roland Westrelin wrote:
> > >> http://cr.openjdk.java.net/~roland/8027626/webrev.00/
> > >>
> > >> The following subgraph is where the bug shows up:
> > >>
> > >> If (18732)
> > >> |     \
> > >> IfTrue IfFalse
> > >> (18734) (18733)
> > >> | |
> > >> | If (12212)
> > >> | |     \
> > >> | IfFalse IfTrue
> > >> | (12214)
> > >> | |
> > >> Region (12183)
> > >>
> > >> Condition to 12212 is always false so 12214 is replaced by 18733 and
> both branches of If 18732 are directly connected to Region 12183. 18733
> still has dead 12212 as output.
> > >> 12183 doesn't have phis so when it's transformed, If 18732 is
> considered for removal. IfTrue 18734 doesn't have uses anymore so it goes
> away but IfFalse 18733 still has some (dead branch 12212 is not yet
> removed).
> > >> An If in the dead branch 12212 is processed. Range check smearing
> follows dominator controls until 18733, tests whether the If is a range
> check and the assert fires because the If only has one projection.
> > >>
> > >> So we’re trying to optimize a dead branch. I fixed it by making the
> range check code more robust.
> > >>
> > >> Roland.
> > >>
> >
> >
>
>
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