RFR(S) 8077504: Unsafe load can loose control dependency and cause crash

[Vladimir Kozlov]

I agree that we have to pass parameter to GraphKit::make_load().
I thought we can avoid it for LoadNode::make() but it has transform for 
compressed oops. AARGH!

Add comment to code in library_call.cpp why we set flag to false.

BTW, should we modify LoadNode::hash() to include _depends_only_on_test 
and prevent igvning?

Thanks,
Vladimir

On 4/24/15 1:03 AM, Roland Westrelin wrote:
>
>> Vladimir suggested privately to set _depends_only_on_test to true in the constructor and then use an explicit call to a new a method set_depends_only_on_test() to set it to false in the rare cases where it’s needed. That feels better indeed. What do you think?
>
> Actually, using a set_depends_only_on_test() method doesn’t work well. In LibraryCallKit::inline_unsafe_access() the node returned by make_load() may have been transformed already and we could call set_depends_only_on_test() on a node that doesn’t need to be pinned. The call to set_depends_only_on_test() would have to be in LoadNode::make(). I went with default parameters instead to keep the change small:
>
> http://cr.openjdk.java.net/~roland/8077504/webrev.01/
>
> Roland.
>