An example of substituability test that is recursive

[forax at univ-mlv.fr]

> De: "Karen Kinnear" <karen.kinnear at oracle.com>
> À: "Remi Forax" <forax at univ-mlv.fr>
> Cc: "John Rose" <john.r.rose at oracle.com>, "valhalla-spec-experts"
> <valhalla-spec-experts at openjdk.java.net>
> Envoyé: Jeudi 31 Janvier 2019 21:36:09
> Objet: Re: An example of substituability test that is recursive

> Option #1 was what I was suggesting in the meeting two weeks ago - if this
> starts
> to recurse too deeply, create a worklist - which should give you the same
> result.

> If you switch to .Equals - you might get a different result …

yes, you are right, i did not understand what you mean by "expected behavior", my bad on that. 

> thanks,
> Karen

regards, 
Rémi 

>> On Jan 31, 2019, at 1:46 PM, [ mailto:forax at univ-mlv.fr | forax at univ-mlv.fr ]
>> wrote:

>>> De: "John Rose" < [ mailto:john.r.rose at oracle.com | john.r.rose at oracle.com ] >
>>> À: "Remi Forax" < [ mailto:forax at univ-mlv.fr | forax at univ-mlv.fr ] >
>>> Cc: "Karen Kinnear" < [ mailto:karen.kinnear at oracle.com |
>>> karen.kinnear at oracle.com ] >, "valhalla-spec-experts" < [
>>> mailto:valhalla-spec-experts at openjdk.java.net |
>>> valhalla-spec-experts at openjdk.java.net ] >
>>> Envoyé: Jeudi 31 Janvier 2019 19:05:33
>>> Objet: Re: An example of substituability test that is recursive

>>> On Jan 31, 2019, at 6:34 AM, [ mailto:forax at univ-mlv.fr | forax at univ-mlv.fr ]
>>> wrote:

>>>> The other solution is to say that == should do an upcall to equals (after the
>>>> null checking and the class checking), if equals throw a StackOverflow, it's
>>>> the expected behavior because the user is in control of that behavior.

>>> What you are doing here, I think, is exposing a requirement
>>> that we *don't* use the control stack for recursion on subst.
>>> testing (or hashing). That's a reasonable requirement.
>>> It leads to a worklist algorithm for doing this tricky thing,
>>> just like we had to do many times in the JIT.

>> IMO that the other solution,
>> solution 1: you use a worklist (and also perhaps a marking algorithm to avoid to
>> crawle the DAG)
>> solution 2: you claim it's too complex and you just let the user deal with it by
>> calling equals() (and provide a way for a user to call the default subst).

>> Rémi