Calling Convention microbenchmark

[Tobias Hartmann]

Hi,

I wrote a simple benchmark to measure the impact of the calling/return convention optimization in
the optimal case when inlining fails due to a megamorphic interface call:
http://cr.openjdk.java.net/~thartmann/valhalla/cc_benchmark/

With default flags the throughput is 36.615 (± 2.668) ops/us on my machine and without the calling
and return convention optimizations it is 24.105 (± 0.899) ops/us. So with this benchmark, the
calling convention optimization improves throughput by 34%.

Of course it's just a microbenchmark so please take this with a grain of salt (one can probably
design a microbenchmark that shows the reverse). If there are no objections, I'll push this.

Best regards,
Tobias