Re: Some JIT compilation challenges

[Coda Highland <chighland@...>]

On Wed, Feb 10, 2016 at 12:42 PM, Dibyendu Majumdar
<mobile@majumdar.org.uk> wrote:
> On 10 February 2016 at 12:32, Hisham <h@hisham.hm> wrote:
>> On 8 February 2016 at 20:02, Dibyendu Majumdar <mobile@majumdar.org.uk> wrote:
>>> LLVM has the concept of a Module which equates to a 'translation unit'
>>> - within which there can be many functions.
>>>
>>> In Ravi at present each function is put into its own module - this has
>>> the advantage that a function is independent of every other function
>>> and when it becomes garbage, the collector releases resources.
>>>
>>> The model in Ravi doesn't scale very well - at least in terms of
>>> memory usage. I assume that each module in LLVM carries some overhead.
>>> It would be nice if multiple functions could be put into a module.
>>
>> This is guesswork, but I think that in idiomatic Lua function lifetime
>> falls into two main categories:
>>
>> * long-lived functions that are part of a Lua module - their lifetime
>> is associated to the lifetime of the enclosing module table, which is
>> usually the lifetime of the program
>> * short-lived closures that are created "inline" by other functions -
>> code that does stuff such as `return function() ... end`, where the
>> resulting function is used and then thrown away
>>
>> For the former, I think you shouldn't worry about GC a lot. I'd make a
>> Lua module one big LLVM translation unit, add all declared functions
>> there and attach the lifetime of the LLVM unit to the Lua module
>> table.
>>
>> For the latter, I think in most cases these short-lived functions
>> won't be worth JITting anyway.
>>
>
> Thanks Hisham, this sounds like a sensible approach.
>
> Regards
> Dibyendu
>

The problem with this approach:

mt = {
  __index = function(t, k) end,
  __newindex = function(t, k, v) end
}

Are these functions "declared" in the module, or are they defined inline?

function closure_based_object()
  var private_member = 123
  return { get_value = function() return private_member end }
end

What about this one?

/s/ Adam