[8u] RFR: 8221355: Performance regression after JDK-8155635 backport into 8u

[Roland Westrelin]

>> The left over comment is misleading, though, which I've now removed:
>> http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8221355/02/webrev/
>
> ...but now I am confused how that patch is supposed to work. It seems to me it accepts the accesses
> to off-heap when object passed it is actually null, but not transparently-null for the compiler?
> That is probably acceptable, but maybe someone savvy in this code can take a look? Vladimir I, Roland?

When base is known to be null, this patch causes c2 to not intrinsify
object accesses and the native method is called. Without this patch, c2
doesn't intrinsify object accesses unless it knows base to be not null
which is indeed too conservative.

That looks good to me.

Roland.