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On 9/21/2011 12:55 PM, Lorenzo Donati wrote:
Is there already a "No-Frills Introduction to Lua 5.1 VM
Instructions" for 5.2 VM [1] or any equivalent higher level
documentation (higher than browsing the source, I mean)?

Nope, I plan to focus on LuaSrcDiet (via Yueliang). Probably after the official 5.2 release...

I think a 5.2 update to No-Frills should switch back to luac.

Why don't you take it up? It seems to be a popular doc. I'll help out and you put your name first. :-) :-)

Or at least a document describing the differences between 5.1 and
5.2 that can be found when browsing a VM listing?

None that I know of.

Playing with luac listings in 5.2 I noticed a GETTABUP mnemonic.
Any more differences?

Better to look at the opcodes, then lvm, and trace calls to other files from there.

On a related note, out of curiosity I wonder if there is something
like an "assembler" targeting Lua VM. I know Lua VM specification
is a Lua implementation detail, but I'm curious to know if someone
has tried this way to enhance the performance of Lua in
time-critical code (assuming that hand-crafted Lua bytecode could
squeeze some cycles out of the VM).

and also something by Zed Shaw in the past, IIRC.

I don't think writing out bytecode assembly-style will give big performance wins. It's still interpreting... Mike Pall's Lua interpreter is already a lot faster, let alone the JIT. Most things that people have thought of will probably need modification of Lua source code (for example, a recent thread about reducing lookups).

Maybe you want to try adding some super-instructions and see if there is a significant performance change -- what I would be real interested in right now is instruction traces and stats to show which bytecode pair (or chain) is most frequent...

That said, I try to code a reasonable algorithm and that's it. Silicon is too cheap and it has wiped out most extreme optimization practices. All the same, as academic exercises, it's an interesting area.

Any pointer appreciated!

Kein-Hong Man (esq.)
Kuala Lumpur, Malaysia