[aarch64-port-dev ] RFR(XS): 8221995: AARCH64: problems with CAS instructions encoding

[Dmitrij Pochepko]

Hi all,

please review small patch for JDK-8221995: AARCH64: problems with CAS 
instructions encoding
webrev: http://cr.openjdk.java.net/~dpochepk/8221995/webrev/

Patch fix 3 problems:
- specification allows addressing register to be SP, while current 
hotspot encoding implementation hits assert in this case
- specification allows data register(s) to be ZR, while current hotspot 
encoding implementation hits assert in this case
- all pair CAS instructions  (CASP*) are encoded incorrectly in bit 23, 
which leads to another instructions generation instead (CAS*B and CAS*H)

Current code shape doesn't generate CAS* instructions using affected 
cases. That is why these problems wasn't found before.

Testing:

I generated code with CAS and CASP with and without patch. Patched 
version hits no asserts while using zr and sp registers. And casp* 
instruction now generated correctly.
CR: https://bugs.openjdk.java.net/browse/JDK-8221995

Thanks,
Dmitrij