[Vm-dev] Weird problem when adding a method to StackInterpreter

[Eliot Miranda]

Hi Mariano,

On Thu, Dec 22, 2011 at 1:12 AM, Mariano Martinez Peck <
marianopeck at gmail.com> wrote:

>
>
>
>>>
>>> Moreover, when I ADD those lines, apart from the make error, when
>>> translating from SLANG to C, if I open a Transcript I see these
>>> "suspicious" lines:
>>>
>>> Removed findNewMethodInClass: because it refers to the local variable
>>> localSP of interpret.
>>> But it is either used outside of interpret or exported!!
>>> Removed lookupInMethodCacheSel:class: because it refers to the local
>>> variable localSP of interpret.
>>> But it is either used outside of interpret or exported!!
>>>
>>> BUT, none of those methods access localSP.
>>>
>>> Any idea of what can be wrong?
>>>
>>
>> For some reason  lookupInMethodCacheSel:class: is not being inlined.
>>  Since it uses localSP via internalStackValue: it must be always inlined
>> into the body of interpret.  What I don't know is why adding a send of
>> traceObjectusage: after internalStackValue: causes inlining to fail.
>>
>
>
> Hi Eliot. I did some more tests and it even fails WITHOUT using
> #traceObjectUsage:  .  Just adding the line "rcvr := self
> internalStackValue: argumentCount."  at the beginning of
> #lookupInMethodCacheSel:class:   will cause the problem. So, the following
> even fails:
>
> lookupInMethodCacheSel: selector class: class
>     "This method....."
>
>     | hash probe rcvr |
>     <inline: true>
>     <asmLabel: false>
>     rcvr := self internalStackValue: argumentCount.
>     hash := selector bitXor: class.  "shift drops two low-order zeros from
> addresses"
> ......
>
>
> Weird ehh, because you use #internalStackValue:  along StackInterpreter in
> a lot of other places and you don't have problems there.
>

Turns out it's not weird at all.  Since  lookupInMethodCacheSel:class: is
used outside of interpret in findNewMethodInClass: and in callback lookup
it can't be inlined and hence can't access localSP.  If you want to get the
receiver you'll need to use stackValue: *and* you'll need to ensure that
stackPointer is updated when calling lookupInMethodCacheSel:class: from
internalFindNewMethod (see externalizeFPandSP), which may slow down the
interpreter slightly.


>
>
>>  You're going to have to delve into the inliner in Slang.  This is, um,
>> not fun.  I liken it to getting hit on the head with a stick by your guru,
>> except that no enlightenment results.  Good luck.
>>
>>
> :(   thanks.
>
>
>
>>
>>> Thanks in advance,
>>>
>>>
>>> --
>>> Mariano
>>> http://marianopeck.wordpress.com
>>>
>>>
>>>
>>
>>
>> --
>> best,
>> Eliot
>>
>>
>>
>
>
> --
> Mariano
> http://marianopeck.wordpress.com
>
>
>


-- 
best,
Eliot
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