[15] RFR(XS): 8239069: C2: SIGSEGV in IdealGraphPrinter::walk_nodes due to C->root() being NULL

[Christian Hagedorn]

Thank you Nils and Tobias for your reviews!

Best regards,
Christian

On 14.02.20 11:43, Tobias Hartmann wrote:
> +1
> 
> Best regards,
> Tobias
> 
> On 14.02.20 11:41, Nils Eliasson wrote:
>> Hi Christian,
>>
>> Looks good!
>>
>> Best regards,
>> Nil
>>
>> On 2020-02-14 10:56, Christian Hagedorn wrote:
>>> Hi
>>>
>>> Please review the following patch:
>>> https://bugs.openjdk.java.net/browse/JDK-8239069
>>> http://cr.openjdk.java.net/~chagedorn/8239069/
>>>
>>> This happens for the method in the replay file because C2 calls Compile::record_failure() twice
>>> consecutively which calls Compile::print_method() each time. In the first call of
>>> Compile::record_failure(), it sets _root to NULL after printing the ideal graph [1]. In the second
>>> call of Compile::record_failure(), it calls Compile::print_method() again. But this time C->root()
>>> is NULL. As a result, it crashes later at [2] when trying to dereference 'start' which is
>>> C->root() and therefore NULL.
>>>
>>> The fix is straight forward to not print the ideal graph if the root node to start the printing is
>>> NULL. This crash only happens in rare cases.
>>>
>>>
>>> Thank you!
>>>
>>> Best regards,
>>> Christian
>>>
>>>
>>> [1] http://hg.openjdk.java.net/jdk/jdk/file/f82f59ef79f0/src/hotspot/share/opto/compile.cpp#l3940
>>> [2]
>>> http://hg.openjdk.java.net/jdk/jdk/file/f82f59ef79f0/src/hotspot/share/opto/idealGraphPrinter.cpp#l622
>>>
>>