[9] RFR(S): 8066763: fatal error "assert(false) failed: unexpected yanked node" in postaloc.cpp:139

[Tobias Hartmann]

Thanks, Vladimir.

Best,
Tobias

On 11.12.2014 10:52, Vladimir Kozlov wrote:
> Good.
> 
> Thanks,
> Vladimir
> 
> On 12/11/14 1:49 AM, Tobias Hartmann wrote:
>> Thanks, Vladimir.
>>
>> I renamed the variable to 'in':
>>
>> http://cr.openjdk.java.net/~thartmann/8066763/webrev.01/
>>
>> Best,
>> Tobias
>>
>> On 11.12.2014 10:28, Vladimir Kozlov wrote:
>>> Looks good but rename local from 'req' (required) to 'in' (input) or 'dead'.
>>>
>>> Thanks,
>>> Vladimir
>>>
>>> On 12/11/14 1:14 AM, Tobias Hartmann wrote:
>>>> Hi,
>>>>
>>>> please review the following patch.
>>>>
>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8066763
>>>> Webrev: http://cr.openjdk.java.net/~thartmann/8066763/webrev.00/
>>>>
>>>> Problem:
>>>> A null check for an oop loaded by a LoadNNode (300) consists of a CmpNNode
>>>> (388), a BoolNode (356) and a IfNode (357) [1].
>>>> After matching, the CmpNNode is replaced by a testN_reg node (56) and a jmpCon
>>>> node (55) [2]. With implicit null checks enabled (default), the compiler
>>>> notices
>>>> that the oop is accessed by a nearby loadINode (131) and optimizes the code by
>>>> using an implicit null check: Instead of checking the oop explicitly, the
>>>> loadINode is moved upwards and executed without a check. Code is added to
>>>> handle
>>>> the SIGSEGV and throw the corresponding NullPointerException [3].
>>>>
>>>> The problem is that after the optimization the testN_reg node is dead (see [3])
>>>> and triggers the assert in the register allocator. With implicit null checks
>>>> disabled (-XX:-ImplicitNullChecks) the bug does not appear.
>>>>
>>>> Solution:
>>>> The proposed fix checks for dead input nodes after removing the old compare
>>>> node. This removes the dead testN_reg node (see [4]).
>>>>
>>>> Testing:
>>>> - Failing test
>>>> - JPRT
>>>>
>>>> Thanks,
>>>> Tobias
>>>>
>>>> [1] https://bugs.openjdk.java.net/secure/attachment/24158/1_before_matching.png
>>>> [2]
>>>> https://bugs.openjdk.java.net/secure/attachment/24187/2_global_code_motion.png
>>>> [3]
>>>> https://bugs.openjdk.java.net/secure/attachment/24159/1_global_code_motion.png
>>>> [4]
>>>> https://bugs.openjdk.java.net/secure/attachment/24161/3_global_code_motion.png
>>>>