[Vm-dev] [squeak-dev] Bug in PolygonMorph>>#filledForm

[Nicolas Cellier]

I do not observe the artifacts at same smear step (nor any other) with
VM [CoInterpreterPrimitives VMMaker.oscog-eem.2266] 5.0.201708312323

That's just 222 commits to bissect...

Le ven. 21 févr. 2020 à 23:00, Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> a écrit :

> There's already a problem with end 2018 VM
> VM [CoInterpreterPrimitives VMMaker.oscog-eem.2488] 5.0.201812040127
>
> Le ven. 21 févr. 2020 à 22:48, Nicolas Cellier <
> nicolas.cellier.aka.nice at gmail.com> a écrit :
>
>> Interesting case to debug...
>> In 64bits VM, a problem first appears in first smear:distance: operation
>> (direction 1 at 0 to the right) at skew=16...
>>
>> [image: Capture d’écran 2020-02-21 à 22.24.03.png]
>>
>>
>> It seems that we copy bits too far to the right (hence we overwrite the
>> bottom rows)
>> Fortunately, the artefacts outside polygon bounds disappear at final
>> bitAnd operation, but that's scary!
>>
>> It could be:
>> - case of overlap detection failure (#checkSourceOverlap), but the code
>> did not change
>> - bad initialisation in #sourceSkewAndPointerInit (the one I corrected in
>> 2019)
>>  https://github.com/OpenSmalltalk/opensmalltalk-vm/issues/426
>> - bug in #copyLoop (which I also corrected in 2019)
>> https://github.com/OpenSmalltalk/opensmalltalk-vm/issues/441
>>
>> Weird kind of integer overflow? (I've made most of the int unsigned, so
>> this might not be detected by UB sanitizer).
>>
>> Or could it be that the extra buffer overrun that I removed did have a
>> side effect of filling more gaps?
>> It would be interesting to observe what happens at same #smear:distance:
>> step with older VM.
>>
>> Le ven. 21 févr. 2020 à 20:39, Stéphane Rollandin <lecteur at zogotounga.net>
>> a écrit :
>>
>>> > Hmmm... the form was still filled in Squeak 5.1 (Update 16549),
>>> > VM 201701311639 (32-bit). Not so in Squeak 5.2.
>>>
>>> Yes, but that same 5.1 image with a current VM has the problem...
>>>
>>> Stef
>>>
>>>
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