Re: [ANN] LuaJIT Roadmap 2012/2013
- From: Mike Pall <mike-1206@xxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Thu, 14 Jun 2012 03:20:00 +0200
Geoff Leyland wrote:
> I'm hoping it'll transform this:
>
> point = {}
> function point:new(x, y)
> self.__index = self
> return setmetatable({x=x, y=y}, self)
> end
> function point.__add(a, b)
> return point:new(a.x + b.x, a.y + b.y)
> end
>
> do
> local a, b = point:new(1, 1), point:new(2, 2)
> for i = 1, 1000 do
> a = (a + b) + b
> end
> io.stderr:write(a.x, ", ", a.y)
> end
>
> into this:
>
> do
> local ax, ay, bx, by = 1, 1, 2, 2
> for i = 1, 1000 do
> ax = ax + bx + bx
> ay = ay + by + by
> end
> io.stderr:write(ax, ", ", ay)
> end
Yes, more or less. Inside the loop everything will be computed in
registers. There's still a 'point' allocation at the start of the
loop. And another 'point' object will be materialized from the
registers when the loop exits (it'll be eliminated if/when that
side trace is compiled eventually).
BTW: That 'self.__index = self' line should be outside of the
allocation function. You're performing a write to the metatable
every time -- never do that! That's a performance hit even for
plain Lua, since it invalidates the negative metamethod cache.
Oh, and 'local point = {}' ...
--Mike
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