Re: Constant folding

[Kein-Hong Man <mkh@...>]

Adam D. Moss wrote:
> Mike Pall pointed out to me that the Lua 5.1 compiler
> started to use constant folding optimizations at some
> point in its development lifetime, which had somehow
> escaped me previously.
>
> Thanks to the Lua authors for that; e.g. now I can
> write stuff like degrees-to-radians conversion in a
> more obvious way, at least, without fear of wasting
> VM instructions. :)

It is not heavy-duty constant folding, though. According to my 
observations, the terms of an expression are not reordered, so the 
following is not optimized:

  local a = a+1+2

since it is parsed as:

  local a = (a+1)+2

It appears the rule is that such optimization opportunities are 
checked in the order the expression is parsed, and for binary 
operators, both terms must be a number.

Also, placing local declarations without assignments at the very 
beginning of a function will eliminate some LOADNILs.

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