[16] RFR(S): 8247743: Segmentation fault in debug builds due to stack overflow in find_recur with deep graphs

[Christian Hagedorn]

Hi

Please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8247743
http://cr.openjdk.java.net/~chagedorn/8247743/webrev.00/

The testcase creates a deep graph with a lot of nodes on a chain. When 
running with the specified test flags, it recursively calls 
Node::find_recur() for each node discovered which eventually results in 
a segmentation fault due to a stack overflow (around 10000 calls due to 
such a long chain of nodes). The fix just converts the recursive 
algorithm into an iterative one to avoid a segmentation fault. This is 
similar to JDK-8246203 [1].

I additionally removed Node::find_ctrl() and its special handling in the 
algorithm since it is not used.

There is actually another problem with the recursive version. When 
running the testcase without -XX:CompileOnly=compiler/c2/TestFindNode, 
it will spin forever inside [2] because there is a debug_orig node cycle 
and the loop does not break based on the debug_orig nodes being visited. 
This is also fixed in the patch.

Thank you!

Best regards,
Christian


[1] https://bugs.openjdk.java.net/browse/JDK-8246203
[2] 
http://hg.openjdk.java.net/jdk/jdk/file/e2622818f0bd/src/hotspot/share/opto/node.cpp#l1589