Re: upvals in Lua bytecode

[Tony Finch <dot@...>]

Florian Weimer <fw@deneb.enyo.de> wrote:
>
> Anyway, to me, the local-vs-global discussion is tied to the module
> system and some sort of phase distinction in the compiler.  If there
> was a way to plug into global name lookup in the compiler, we could
> accurately describe to the compiler what global variables exist, and
> the compiler could error out for unknown global variables.

I think this is over-ambitious. You can get a lot of benefit from just
checking that variables are declared before use within a module. It then
becomes easy to find which global variables exist using grep - though it
gets interesting if you play games with function environments.

> It might even be possible to compile expressions such as string.byte to
> a constant reference in the byte code, so that the need for the "local
> byte = string.byte" pattern goes away.

LuaJIT does that, but it requires analysis to prove that string.byte is
not assigned to directly or via an alias.

Tony.
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