Micro-optimisation (2 questions)

[Alf21]

Currently i'm working on micro-optimisation of my gamemode.
I didn't found anything, so i'm asking here: Which code runs faster?

if not t.val then
t.val = {}
end

or

t.val = t.val or {}

In addition to this, focussed on improving expressions (lua-users wiki), is there any speed difference between

y = x + 1 + 2

and (unnecessary parentheses)

y = x + (1 + 2)

Thanks!

[Doctor Jew]

That makes no difference in terms of speed.

It's even mentioned on the Logical Operators page that:

A useful Lua idiom is x = x or v
, which is equivalent to
if not x then x = v end

Not sure why you think parentheses would cause any slow down.

[polivilas]

Dont bother yourself with microoptimisation, as it reduces code readability, maintainability, etc. rather, optimize what takes up the most time. FProfiler is a good tool for that.

[Alf21]

hmmm... I tested on my own and did some other searches. There i found the following: https://springrts.com/wiki/Lua_Performance Test 5 concludes that the second way will be a little bit faster. I know that code gets compiled, and maybe the compiled code will be the same. And that's the question - more or less. But your answers compared with the test differs...

@polivilas sure, i know the difference between micro- and macro-optimization. But that was not my question. I wouldn't ask if I did not care ^^ And why not improving the code if it's possible and does not reduce the readability very much. All in all, you are right. ^^

[Doctor Jew]

You really can't use that site you linked for actual assumptions. Garry's Mod is NOT running just Lua. It uses Lua JIT which does a ton of optimizations on it's own which may or may not make many of those performance tests not true.

[c👌de_g🎷]

That's implying all microoptimisations reduce code readability as opposed to a lateral semantic change, or performance-intensive code that relies on each instruction save doesn't exist (maybe less so in Lua but the philosophy still applies).
LuaJIT specifically inlines "or" statements that act like a ternary, specifically when it results in a constant operation (table creation).

[Meow the Cat]

Don't bother with micro-optimization, focus on stuff that can bring major performance improvements.