RFR(sh/jdk8): [backport] 8228369: Shenandoah: Refactor LRB C1 stubs

[Roman Kennke]

> On 11/25/20 10:23 PM, Roman Kennke wrote:
>> It turns out that the aarch64 parts have been incorrect. Please review
>> this webrev instead:
>>
>> http://cr.openjdk.java.net/~rkennke/JDK-8228369-jdk8/webrev.01/
> 
> I believe we need to protect new blocks in c1_LIRAssembler_aarch64.cpp 
> with UseShenandoahGC?

You mean c1_Runtime1_*.cpp? Yeah maybe. Those blocks are by their 
definition Shenandoah-specific, so an assert(UseShenandoah) might be better?

http://cr.openjdk.java.net/~rkennke/JDK-8228369-jdk8/webrev.02/

Roman