RFR(M): 8223051: support loops with long (64b) trip counts

[Tobias Hartmann]

Hi Roland,

First of all, very nice optimization!

>> Tobias might wish to run some regression tests on the final changes.

I've submitted some testing. Will report back once it finished.

> http://cr.openjdk.java.net/~roland/8223051/webrev.02/

Looks good to me.

Some style comments (no new webrev required):

c2_globals.hpp:
- line 785: "if > 0. convert" -> "If > 0, convert"

loopnode.cpp:
- line 504: "check_stride_overflow" is already in 8244504
- line 536: add assert message

loopnode.hpp:
- line 1462: Shouldn't _loop_invokes/_loop_work also be volatile and be incremented atomically?

Best regards,
Tobias