lua-users home
lua-l archive

[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index] [Thread Index]

On Monday, August 19, 2002, at 09:58  AM, Roberto Ierusalimschy wrote:
I'm also just generically curious about this change. What led to it?
What are the tradeoffs?

In Lua 4.0 we already decided to use a whole 32-bit integer for each
instruction, because of alignment problems with arguments inside
bytecodes. But with 32-bit instructions and a stack machine, most
istructions do not use most bits. Also, we know that copying values
is a "slow" operation in Lua (because each value is a structure). Then,
we decided to try this register-based architecture.

Are there any docs on this? How many registers are there and how many are the same after a return from a function call? Is there a return register? How does it deal with lua's multiple return values?

> Now it is difficult to estimate the real gains with that change, because
> there are many other changes too. But I would say that for "opcode
> intensive" code (that is, code with few function calls and lots of
> locals) the gain in performance is around 20%.

Just curious - do you think this reflects the fact that the hw lua typically runs on is register based? Would you still expect a performance improvement if lua were running on stack-based hw(like some forth CPUs)?