[Rd] JIT compiler does not compile closures with custom environments

[Taras Zakharko]

That’s the interim solution I am using right now (manually precompiling most functions), but I generate quite a lot of closures dynamically in my code and the potential performance loss is a bit worrying… I don’t think the current behavior is expected based on what the documentation says.

Cheers, 

Taras



> On 18 Aug 2021, at 16:36, Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
> 
> 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
>