RFR(L): 8206139: [lworld] Re-enable calling convention optimizations

[Roland Westrelin]

Hi Tobias,

> http://cr.openjdk.java.net/~thartmann/8206139/webrev.01/

How does the new entry point interacts with stack banging? Does stack
banging takes extra space on the stack that may allocated by the new
entry point into account?

In sharedRuntime_x86_64.cpp:

4388       // We don't need barriers because the destination is a newly allocated object.

That seems like a risky assumption. We're likely to need load barriers
with concurrent collector too.

Would it be possible to save restore sp in the caller around the call to
the new entry point, then the new entry point would extend the caller's
stack but the compiled code would otherwise use a known constant frame
size? How much harder would it be to support stack walking?

In any case, this is good to push.

Roland.