AArch64 port

[Roman Kennke]

Am Donnerstag, den 17.03.2016, 15:23 +0000 schrieb Andrew Haley:
> FYI:
> 
> This is revised port.  A couple of bugs are fixed, and there is one
> performance improvement which I thought was important.  It is the WB
> stub, which no longer calls out to the C++ runtime code, but instead
> evacuates the object as part of the stub.  Calling out to the runtime
> in the write barrier is very expensive because we have a huge amount
> of CPU state to save and restore.
> 
> http://cr.openjdk.java.net/~aph/aarch64-shenandoah-2/

This looks like a good improvement! I shuold attempt the same on x86.
Do you see improved performance?

Some notes:
- You shouldn't need to check for 128words. If it doesn't fit in the
tlab, you will bail out later. If it does fit, all good.
- If the CAS fails, you should revert the tlab top.
- My upcoming patch will remove the gclab stuff. You should be able to
s/gclab/tlab/ and be fine. Or if you commit first, I'll fix it.

You should have commit access now. Please go ahead and push it.

Roman