[13] RFR(S): 8219807: C2 crash in IfNode::up_one_dom(Node*, bool)

[Tobias Hartmann]

Hi,

please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8219807
http://cr.openjdk.java.net/~thartmann/8219807/webrev.00/

We crash in IfNode::up_one_dom() while walking up the dominator tree because two regions (din3 and
din4) are degraded to copies (for details see the bug comments). The control inputs of these regions
were set to NULL in RegionNode::Ideal() but the nodes were not removed because we were still parsing.

Both regions are on the igvn worklist and will be replaced but the IfNode is processed first and
therefore encounters the NULL control inputs. I think the code should guard against that. The bug is
very old and reproduces since JDK 8 with the regression test.

I will run extended testing as soon as Mach5 is up again.

Thanks,
Tobias