Faster operand stack

[hrj]

• Uses a pre-allocated array.
• Avoids frequent growing and shrinking of array
• Convenience methods for dup* opcodes to avoid frequent pops and pushes

  Benchmark results

I tested with two benchmarks. Compute just computes some fibonacci numbers over and over, and the second one compiles a .java file using javax.tools

Compute

Browser	Before	After	Improvement
Firefox 43	2075ms	1105ms	46%
Chromium 47	1049ms	774ms	26%

Compile

Browser	Before	After	Improvement
Firefox 43	40215ms	30798ms	23%
Chromium 47	26811ms	25197ms	6%

[jvilk]

:clap: Awesome! The code looks great, too.

You can actually figure out how much stack space Java methods require. The Code attribute has the properties maxStack and maxLocals that indicate the needed stack/locals size.

Would you be willing to hook up maxStack and repeat your experiments?

If not, I can merge this as-is.

[hrj]

Thanks! I have used maxStack and pushed the commit. I don't see any noticeable difference in benchmarks though.

Why did you mention maxLocals? I am not very familiar with this stuff hence not sure if I can use it in this PR.

[jvilk]

Typical jvilk over-explaining. My brain is a bit fried from writing up student assignments. It's not relevant.

It's likely that the maxStack change only changes memory consumption a bit, since most JVM methods have a very short operand stack.

Thanks again for this! I'll merge it in.