RFR: keep read barrier on final field access

[Aleksey Shipilev]

On 10/23/2017 03:32 PM, Roland Westrelin wrote:
> http://cr.openjdk.java.net/~roland/shenandoah/rbonfinalinstancefield/webrev.01/

*) String.value and String.coder are effectively stable, see UseImplicitStableValues. Should
GraphKit::load_String_* use ShenandoahOptimizeStableFinals then? Or, we are concerned with the same
bug as we see originally?

*) ...in fact, should ShenandoahOptimizeStableFinals default to "false"?

*) It seems this description applies to ShenandoahOptimizeInstanceFinals too?

 47           "Turn it off for maximum compatibility with reflection or JNI "   \
 48           "code that manipulates final fields."                             \
 49           "Defaults to true. ")                                             \

Thanks,
-Aleksey