Forgot to add: you could define f_env like this to get it compiled:
f_env <- local({
cmpfun(function(x) {
for(i in 1:10000) x <- x + 1
x
})
})
Not as convenient as JIT, but it gets the job done...
Duncan Murdoch
On 18/08/2021 10:33 a.m., Duncan Murdoch wrote:
On 18/08/2021 9:00 a.m., Taras Zakharko wrote:
I have encountered a behavior of R’s JIT compiler that I can’t quite figure
out. Consider the following code:
f_global <- function(x) {
for(i in 1:10000) x <- x + 1
x
}
f_env <- local({
function(x) {
for(i in 1:10000) x <- x + 1
x
}
})
compiler::enableJIT(3)
bench::mark(f_global(0), f_env(0))
# 1 f_global(0) 103µs 107.61µs 8770. 11.4KB 0 4384 0
# 2 f_env(0) 1.1ms 1.42ms 712. 0B 66.3 290 27
Inspecting the closures shows that f_global has been byte-compiled while f_env has not been byte-compiled. Furthermore, if I assign a new environment to f_global (e.g. via environment(f_global) <- new.env()), it won’t be byte-compiled either.
However, if I have a function returning a closure, that closure does get
byte-compiled:
f_closure <- (function() {
function(x) {
for(i in 1:10000) x <- x + 1
x
}
})()
bench::mark(f_closure(0))
# 1 f_closure(0) 105µs 109µs 8625. 0B 2.01 4284 1
497ms
What is going on here? Both f_closure and f_env have non-global environments.
Why is one JIT-compiled, but not the other? Is there a way to ensure that
functions defined in environments will be JIT-compiled?
About what is going on in f_closure: I think the anonymous factory
function() {
function(x) {
for(i in 1:10000) x <- x + 1
x
}
}
got byte compiled before first use, and that compiled its result. That
seems to be what this code indicates:
f_closure <- (function() {
res <- function(x) {
for(i in 1:10000) x <- x + 1
x
}; print(res); res
})()
#> function(x) {
#> for(i in 1:10000) x <- x + 1
#> x
#> }
#> <bytecode: 0x7fb43ec3aa70>
#> <environment: 0x7fb441117ac0>
But even if that's true, it doesn't address the bigger question of why
f_global and f_env are treated differently.
Duncan Murdoch
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