Interpreter and platform specific runtime code use the Access API for all Oop accesses.
We need to prevent GC barriers from clobbering registers which contain live data during such accesses.
The current implementation doesn't support this completely. An enhacement is required for supporting GCs with load barriers.

In addition, the GC interface of zGC and ShenandoahGC use LIR_Assembler::leal with patching in C1 platform code. Patching support is also missing on PPC64.