RFR: 8198571: [JVMCI] must not install wide vector code unless runtime supports it

[Doug Simon]

> On 2 Mar 2018, at 22:12, dean.long at oracle.com wrote:
> 
> Should we also bail out if
> 
> HotSpotReferenceMap::maxRegisterSize(reference_map)) > MaxVectorSize
> 
> or
> 
> is_wide_vector(HotSpotReferenceMap::maxRegisterSize(reference_map))) && !is_wide_vector(MaxVectorSize)
> 
> instead of determining based only on the existence of the safepoint blob?  Otherwise it looks good.

Interesting questions. However, this test is a last line of defense in case a JVMCI compiler doesn't do the feature testing you propose. Its purpose is purely to ensure we do not install code relying on the existence of a certain safepoint handler.

-Doug

> 
> On 3/2/18 8:56 AM, Doug Simon wrote:
>> Thanks Vladimir.
>> 
>> Can I get another review please?
>> 
>> -Doug
>> 
>>> On 23 Feb 2018, at 21:14, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
>>> 
>>> Okay. Then it is good.
>>> 
>>> Thanks,
>>> Vladimir
>>> 
>>> On 2/23/18 11:59 AM, Doug Simon wrote:
>>>> Yes. We have a separate fix for Graal that does what you propose. This is just a last bit of defense to prevent a VM crash in case the bug creeps back into Graal (or any other JVMCI compiler).
>>>> Sent from my iPhone
>>>>> On 23 Feb 2018, at 8:54 pm, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
>>>>> 
>>>>> Hi Doug,
>>>>> 
>>>>> Are you planning changes to check MaxVectorSize value when vectors are generated by Graal?
>>>>> Throwing exception during code installation is very late and expensive (you have to throw out all methods with vectors after spending CPUs to compile them).
>>>>> 
>>>>> Thanks,
>>>>> Vladimir
>>>>> 
>>>>>> On 2/23/18 8:57 AM, Doug Simon wrote:
>>>>>> As shown in https://github.com/oracle/graal/issues/303, a bug in a JVMCI compiler can result in vector code being installed even if the runtime doesn't support it. JVMCI should be defensive and raise an exception in this case.
>>>>>> https://bugs.openjdk.java.net/browse/JDK-8198571
>>>>>> http://cr.openjdk.java.net/~dnsimon/8198571/
>>>>>> -Doug
>