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

[Christian Hagedorn]

Ping - could anyone review it, please? Thanks!

Best regards,
Christian

On 02.07.20 09:33, Christian Hagedorn wrote:
> 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 
>