RFR (XXS): 8026376: assert(false) failed: DEBUG MESSAGE: exception pc already set

[Vladimir Kozlov]

For the record. Christian and I discussed it and decided to remove 
'exception pc' load in deopt_blob on all platforms in separate changes. 
First, it is broken in x86 code anyway (it is not saved in all paths in 
deopt_blob). Second, we return into Interpreter which know nothing (and 
don't care) about compiled code and it does not use this pc data.

Thanks,
Vladimir

On 10/14/13 2:17 PM, Christian Thalinger wrote:
> The reason I've added it is because we do it on x86 but there are comments like this:
>
>    // I think this is useless (throwing pc?)
>    __ movptr(rdx, Address(rsp, RegisterSaver::rdx_offset_in_bytes()));
>
> So we either should read it everywhere or don't.
>
> On Oct 14, 2013, at 11:43 AM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
>
>> Don't read exception pc since it is not needed. You may trash a value in that register.
>>
>> Thanks,
>> Vladimir
>>
>> On 10/14/13 11:19 AM, Christian Thalinger wrote:
>>> https://bugs.openjdk.java.net/browse/JDK-8026376
>>> http://cr.openjdk.java.net/~twisti/8026376/webrev.00/
>>>
>>> 8026376: assert(false) failed: DEBUG MESSAGE: exception pc already set
>>> Reviewed-by:
>>>
>>> It made me suspicious that only the second assert fired (the exception pc check) and not the first one (the exception oop check). I checked all the places where JavaThread::exception_oop_offset() was used to clear the exception oop to see if we also clear the exception pc.
>>>
>>> In the deopt blob we have such a case. On x86 we clear both but on SPARC we don't.
>>>
>>> Added the missing null-store instruction makes the test case pass.
>>>
>>> Reading the exception pc is not really required but I've added it for completeness.
>>>
>