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Performance on variable lookup
John Smith
#1 Posted : Friday, May 8, 2020 9:24:05 AM(UTC)
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Using 2.2.5 stable

test snippet

Code:
::func <- function() {
    return 251*139
}

::T1 <- {T2 = {T3 = {T4 = {func = ::func}}}}

local freefunc = ::func

T1.test <- function():(freefunc) {
    local start = clock()

    local f = ::func

    for (local i = 0; i < 10000000; i++){
        f()
    }

    print(clock() - start)
}

T1.test()


I noticed that in some cases calling functions explicitly using :: is slower than not using it. I find this weird, as I imagine not using it would look through local -> constant -> environment -> root, but using it would skip all directly to root.

However, not calling a function but just looking up (removing '()') does indeed work as intended, with :: being faster in every case.

Using free variables are also slower than using local variables in every case. I thought using a free variable would lookup once, bind the value of the func to the function in compile, and use it as a local var (implicit param) - compared to using a local variable and looking up every time it is called (though I realize it is just once and should not make any difference).

Changing inside the loop, here are my consistent test results

Code:

f()                   : 1.070   : local var
freefunc()            : 1.170   : free var

func()                : 1.430   : global, no prefix
::func()              : 1.320   : global, with ::     faster

T1.T2.T3.T4.func()    : 2.080   : global, no prefix
::T1.T2.T3.T4.func()  : 2.280   : global, with ::     slower



Is this normal?

Also while I know such differences would not matter in most cases, under 2000 loops or whatever, wouldn't it make sense to assign global lookups to local variables every time?
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