Node child/children relation change during Runtime

[Gero Leinemann]

Hi Christian,

thank you for your fast and extensive response.

This is done for certain CallNodes for which the passed arguments
(@Children) may change on every call. But I after reading your answer
and reviewing the code I think I can avoid this. Thanks for the pointer
to IfNode!

Best,
Gero


Am 15.07.2014 14:39, schrieb Christian Wirth:
> Hi Gero,
>
> why do you want to change the order of nodes dynamically; what is the
> reasoning for doing so? We have not yet seen any use-case for that.
>
> Ad 1) It SHOULD count as alteration of the AST. Are you working with
> @Child or with @Children? In any case, you need to invalidate the
> compiled code when you do that (the API does that for you, if it has a
> chance to). E.g. just exchanging two pointers in an @Children array is
> not enough, you manually need to call
> CompilerDirectives.transferToInterpreterAndInvalidate().
>
> Ad 2) and 3) it is very relevant. Again, there is a difference whether
> you use @Child (where you have more controll over what is executed in
> what order) or @Children. Truffle assumes the @Child and the @Children
> array to be constant. If you change it, you have to invalidate your
> code. You can, however, express the execute method(s) in a way that
> they dynamically adopt to your ordering (or control flow). A very
> simple example example is an "IF" node: depending on the result of
> conditionNode, either thenNode or elseNode is executed.
>
> Regards,
> Christian Wirth
>
>
>
> Am 15.07.2014 14:12, schrieb Gero Leinemann:
>> Hello everyone,
>>
>> I'm new to Graal/Truffle and currently working for Michael Haupt on
>> FastR. While trying to understand the FastR code base I've got some
>> questions regarding the creation and mutation of child/children of a
>> Truffle-Node.
>>
>> As far as I understand it, the aim in language implementations using
>> Truffle is to keep the AST stable to get it compiled some time by Graal.
>> Therefore one should avoid adding new children during the lifetime of a
>> Node, as this alters the AST.
>>
>> Now there is a piece of code where a Node is once added to the tree
>> whose children's order is permuted frequently (every 'execute'). My
>> questions are:
>> 1) Does this count as alteration?
>> 2) If no: Is the change of order of children during execution really
>> irrelevant for Truffle/Graal?
>> 3) If no: Is the only thing Truffle/Graal depends on for compilation the
>> proper bidirectional parent <-> child relation which is established by
>> 'Node.insert'/'replace'?
>>
>> Thank you in advance!
>>
>> Best Regards,
>> Gero
>