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

[Taras Zakharko]

Thanks for the explanation, Luke! I’ll keep this behavior in mind. 


> On 18 Aug 2021, at 16:45, luke-tierney using uiowa.edu wrote:
> 
> On Wed, 18 Aug 2021, 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>
> 
> That is right.
> 
>> But even if that's true, it doesn't address the bigger question of why f_global and f_env are treated differently.
> 
> There are various heuristics in the JIT code to avoid spending too
> much time in the JIT. The current details are in the source
> code. Mostly this is to deal with usually ill-advised coding practices
> that programmatically build many small functions.  Hopefully these
> heuristics can be reduced or eliminated over time.
> 
> For now, putting the code in a package, where the default is to byte
> compile on source install, or explicitly calling compiler::cmpfun are
> options.
> 
> Best,
> 
> luke
> 
>> 
>> Duncan Murdoch
>> 
>> ______________________________________________
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>> 
> 
> -- 
> Luke Tierney
> Ralph E. Wareham Professor of Mathematical Sciences
> University of Iowa                  Phone:             319-335-3386
> Department of Statistics and        Fax:               319-335-3017
>   Actuarial Science
> 241 Schaeffer Hall                  email:   luke-tierney using uiowa.edu <mailto:luke-tierney using uiowa.edu>
> Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu <http://www.stat.uiowa.edu/>

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