[Vm-dev] postponing tempVector creation

[Igor Stasenko]

how about debugger
and accessing context state?
it going to be complicated, since at some stages temps not even allocated.


On 16 October 2013 14:53, Clément Bera <bera.clement at gmail.com> wrote:

>
> Hello,
>
> Recently I realized that the tempVector is always created at the beginning
> of the method. In the case of:
>
> foo
>     | temp |
>     true ifTrue: [ ^ self ].
>     [ temp := 1 ] value.
>
> It means that even if the execution flow goes to the quick return
> direction, the tempVector is created even if it is not used. I hacked a bit
> the compiler to lazily create the tempVector when needed (access to temp
> Vector variable or block closure creation), which means here the tempVector
> would be created just before the pushClosure bytecode and not at the
> beginning of the method.
>
> I got as result that this specific method was executed 50,000,000 times
> per second instead of 21,000,000 times per second. Probably because of some
> useless garbage collection avoided.
>
> The problem of this lazy tempVector initialization is that I never know
> where I am in the control flow graph. This means than in the case:
>
> bar
>     | temp |
>     false ifTrue: [ temp := 1 ].
>     [ temp := 2 ].
>
> It is hard to detect where to add the extra bytecode for lazy tempVector
> initialization, because the first time you need it is in a branch, so if
> you create the tempVector in the branch and the execution flow goes in the
> other direction then the tempVector will not have been initialized.
>
> Has any of you already investigated in this direction ? Does it worth it
> to implement that ?
>
> Thanks for any answers.
>
>


-- 
Best regards,
Igor Stasenko.
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