RFR: 8208601: Introduce native oop barriers in C2 for OopHandle

[Erik Österlund]

Hi Nils,

Thanks for the review!

/Erik

On 2018-08-21 11:46, Nils Eliasson wrote:
> Looks good.
>
> // Nils
>
>
> On 2018-08-01 13:17, Erik Österlund wrote:
>> Hi,
>>
>> There is currently no way of doing IN_NATIVE accesses in C2 using its 
>> access API. These are required to properly access OopHandle, used to 
>> access the Java class mirrors (because they will now start requiring 
>> load barriers). In order to support (concurrent) class unloading in 
>> ZGC, this support must be added.
>>
>> In this patch, I add an access_load API for loading IN_NATIVE oops, 
>> and use it to load class mirrors (which is logically an 
>> OopHandle::resolve, which happened to have been an indirect load 
>> before as nobody had load barriers on it). In the various code 
>> recognizing the shape of a mirror load to optimize the code, I have 
>> added a check if a node is a GC barrier and to then step over it in 
>> order to match the mirror load.
>>
>> In order to recognize and step over the load barriers in ZGC 
>> properly, I added support for recognizing the barrier shapes not just 
>> before macro expansion (LoadBarrierNode), but also after macro 
>> expansion (as required by the matching code), which involves checking 
>> for phi nodes with with LoadBarrierSlowRegNode phi->in(1), and then 
>> stepping over to phi->in(2), as well as recognizing projections to 
>> such shapes. LoadBarrierSlowRegNode is used in all barrier expansions 
>> except for atomic xchg, but that is fine as we don't use that on 
>> class mirrors.
>>
>> I have checked that the shapes are recognized and that no regressions 
>> are introduced with these changes through a bunch of benchmarks in 
>> gc-test-suite.
>>
>> Webrev:
>> http://cr.openjdk.java.net/~eosterlund/8208601/webrev.00/ 
>> <https://link.getmailspring.com/link/1533049674.local-48cfadc1-4a64-v1.3.0-fd741eb7@getmailspring.com/0?redirect=http%3A%2F%2Fcr.openjdk.java.net%2F%7Eeosterlund%2F8208582%2Fwebrev.00%2F&recipient=aG90c3BvdC1jb21waWxlci1kZXZAb3Blbmpkay5qYXZhLm5ldA%3D%3D>
>> Bug URL:
>> https://bugs.openjdk.java.net/browse/JDK-8208601 
>> <https://link.getmailspring.com/link/1533049674.local-48cfadc1-4a64-v1.3.0-fd741eb7@getmailspring.com/1?redirect=https%3A%2F%2Fbugs.openjdk.java.net%2Fbrowse%2FJDK-8208582&recipient=aG90c3BvdC1jb21waWxlci1kZXZAb3Blbmpkay5qYXZhLm5ldA%3D%3D>
>>
>> Thanks,
>> /Erik
>> Open Tracking
>