RFR: 8166188: G1 Needs pre barrier on dereference of weak JNI handles

[Kim Barrett]

> On Feb 14, 2017, at 11:26 AM, Mikael Gerdin <mikael.gerdin at oracle.com> wrote:
> 
> Hi Kim,
> 
> On 2017-02-13 05:25, Kim Barrett wrote:
>> Here's the updated webrevs, incorporating feedback received so far.
>> 
>> full: http://cr.openjdk.java.net/~kbarrett/8166188/hotspot.05/
>> incr: http://cr.openjdk.java.net/~kbarrett/8166188/hotspot.05.inc/
> 
> I think your change is ready to go, consider it Reviewed by me.

Thanks.

> 
> I can't really say that I think this looks good due to the fact that I'm still traumatized by JavaCallArguments and how it uses something I've come to think of as "alternative code" to handle oop parameters but that is something that I hope we can clean up at some point in the future.
> 
> Thanks for fixing this!
> /Mikael
> 
>> 
>> For x86 and ARM I added resolve_jobject functions to their respective
>> macroAssembler files, and call those to generate the return object
>> handling code.  Merging the two cases for Sparc is harder and I'm
>> going to leave it to someone else.  I'm also leaving any such merging
>> for other (non-Oracle) ports to their respective maintainers.
>> 
>> Rewrote the error checking in SignatureChekker::check_obj to simplify
>> the control flow and provide more information.  Rather than
>> conditionally selecting between ReportJNIFatalError or assert to
>> report problems, instead just always use guarantee.  Recall that we
>> only get here if CheckJNICalls or in a debug build.  This made
>> SignatureChekker::_thread unused, so removed it.