[External] Re: JIT compiler does not compile closures with custom environments

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)    103?s 107.61?s     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)    105?s    109?s     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