G1RSBarrierRegionFilter is a bool develop flag, defaulting to true. It controls whether the post-barrier checks for target and new value being in the same region, filtering out card table updates when they are.

At present, only the ppc and sparc targets check this flag, and then only for the interpreter and C1. C2 has platform-independent compiler code for generating the check, and it's not conditionalized by the flag.

In the original G1 integration commit, this flag was only examined by the sparc-specific MacroAssembler code, in conjunction with code to record statistics for the filter.

Either support for this flag should be added to the other targets and to C2, or the flag should be removed. I'm thinking removal makes more sense.