RFC: Remove DONT_USE_REGISTER_DEFINES on Sparc?

[Per Liden]

Hi,

We recently ran into an unfortunate naming conflict, concerning "G1" the 
garbage collector vs. "G1" the sparc register. We'd like to be able to 
use "G1" as an enum value in various GC code, but register_sparc.hpp 
defines "G1" as a macro, which obviously breaks things.

We're very reluctant to sprinkling #define DONT_USE_REGISTER_DEFINES in 
GC code. An alternative would be to simply remove this optimization in 
the sparc code. The comment in register_sparc.hpp suggests that this was 
done to reduce the size of libjvm.so.

I applied a patch[1] to remove the sparc macros and libjvm.so grew by 
~0.3% (66450K->66682K). Builds available here[2] and here[3].

Given that the libjvm.so growth doesn't seem that bad, would people be 
ok with removing the register defines on sparc? If so I'll file a bug 
and send out the patch for formal review.

The patch currently removes all register defines. There are of course 
alternatives here in case someone things the libjvm growth is 
unacceptable, like only remove general register, only G* registers, etc.

/Per

[1] http://cr.openjdk.java.net/~pliden/remove_G1_define_on_sparc/webrev.0

[2] 
https://java.se.oracle.com/artifactory/jdk-dev-local/jdk/personal/per.liden/2018-03-22-0935410.per.liden.hs/bundles/solaris-sparcv9/

[3] 
https://java.se.oracle.com/artifactory/jdk-dev-local/jdk/personal/per.liden/2018-03-22-0952297.per.liden.hs/bundles/solaris-sparcv9/