RFR: JDK-8217909: Make unused r12 register (without compressed oops) available to regalloc in C2

[Roman Kennke]

>> I started a version based on Dean's approach:
>>
>> http://cr.openjdk.java.net/~rkennke/JDK-8217909/webrev.01/
>>
>> Unfortunately it barks on ptr_reg class:
>>
>> assert fails
>> /home/rkennke/src/openjdk/jdk-jdk/src/hotspot/share/adlc/formsopt.hpp
>> 246: User defined register classes are not allowed to spill to the stack.
>>
>> Interestingly, it doesn't do that when I only handle any_reg class.
>> However, I am not sure what that means or how to fix it. Any hints?
> You could maybe use reg_class_dynamic to do this. See the AArch64 ad
> file for an example.

Did you mean to say the way to go is my original patch? ;-)

http://cr.openjdk.java.net/~rkennke/JDK-8217909/webrev.00/

Roman