RFR(XS) 8027388: JVM crashes with SIGSEGV (0xb) at pc=0x00000001077cbbf6

[Igor Veresov]

The fake null store doesn’t quite work and breaks the pointer compare optimization in escape analysis. I have to go back and think of a better solution.

igor

On Dec 23, 2013, at 7:48 PM, Igor Veresov <igor.veresov at oracle.com> wrote:

> I’ll fix that. Thanks for the review, Chris!
> 
> igor
> 
> On Dec 23, 2013, at 7:22 PM, Christian Thalinger <christian.thalinger at oracle.com> wrote:
> 
>> +         // assume that the result of the LoadP is the the argument of the StoreP.
>> Typo: “the the”
>> 
>> The fix is good.
>> 
>> On Dec 21, 2013, at 12:53 AM, Igor Veresov <igor.veresov at oracle.com> wrote:
>> 
>>> Given the following graph, escape analysis currently fails to track the fact that we can load from null. 
>>> 
>>>  Allocate A <-- ...---------- StoreP
>>>  Allocate B <-- ... - AddP <--/
>>>           \
>>>            Phi <--- ... -- AddP <--- LoadP
>>>  null <-- /
>>> 
>>> The AddPs may refer to the same field of B, however, B could be null so we cannot assume that the result of the LoadP is the the argument of the StoreP.
>>> We don't want to add edges to null_obj for performance reasons, so we handle this case by faking the effect of storing a null to this field, which will force a potential non-escaping object (that is also stored to this field) to be marked as not scalarizable. The end result is the same -- we cannot predict that value of the field. Notice that if B is non-escaping it will be made non-scalarizable as well because the field has two bases.
>>> 
>>> Webrev: http://cr.openjdk.java.net/~iveresov/8027388/webrev.00/
>>> Testing: jtreg, ctw
>>> 
>>> Huge thanks to Vladimir for discussions and helping me out with this problem!
>>> 
>>> igor
>> 
> 

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