[15] RFR(XS): 8246153: TestEliminateArrayCopy fails with -XX:+StressReflectiveCode

[Tobias Hartmann]

Hi,

please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8246153
http://cr.openjdk.java.net/~thartmann/8246153/webrev.00/

With -XX:+StressReflectiveCode, loads from the layout helper emitted by GraphKit::get_layout_helper
are not folded (usually done via LoadNode::Value -> LoadNode::load_array_final_field). As a result,
the control input of the AllocateNode does not directly point to the MemBar but to the
initial_slow_test emitted by GraphKit::new_instance that has not been folded either.

Instead of using the control input to find the MemBar when removing allocations after scalar
replacement, we should simply use the memory input.

Thanks,
Tobias