[Vm-dev] Access to arguments in the stack vm

[Hernan Wilkinson]

Thank you again! pretty clear!
And yeah, we all have to many thing to do :-)

Cheers!
Hernan.

On Tue, Oct 9, 2018 at 9:33 AM Clément Béra <bera.clement at gmail.com> wrote:

>
> Hi,
>
> Not sure there is documentation specifically about that. I think the 2
> sentences in the previous mail I wrote basically cover the whole idea,
> there are not really hidden tricks.
>
> There's documentation about the context to stack mapping in the
> interpreter though which involves a lot of internal/external code, but it's
> a more complicated concept.
>
> I think the general problem is that interpreters are very different from
> standard C programs and C compilers struggle really hard to produce good
> code for any interpreter that anyone writes. For good interpreter
> performance you need to write the exact good sequence of native
> instructions that execute each bytecode instruction. So people tend to
> write interpreters in their own abstract assembly (See V8's ignition, JSC
> LLInt or the openJDK assembly templates) to work around the C compiler. In
> OpenSmalltalkVM, it was decided to use C + GNU extension. GNU extensions
> allow to fix registers (IP/SP/FP) in the main interpreter loop. You can see
> the Gnuifier>>gnuify method in VMMaker which basically does the GNU
> transformation in the C code. That solves part of the problem. The
> StackInterpreter is between 0% and 20% slower than the OpenJDK interpreter
> on a wide range of benchmarks, so I'd say it's quite a good trick given the
> engineering power we have compared to the OpenJDK. Obviously the difference
> is higher in the JIT.
>
> One of my dream is to rewrite the interpreter on top of Cog's back-end in
> a similar way that ignition is built on top of Turbofan backend in V8. That
> would allow us to boost interpreter performance but also to have quick
> interactions between the interpreter and jitted code allowing to use the
> interpreter more extensively for non frequently used code and that way we
> could share more code between the interpreter and the JIT. That would mean
> we won't really have those internal/external code. But there are so many
> things to do :-).
>
> I'm glad I could help,
>
> Best!
>
>
> On Tue, Oct 9, 2018 at 1:47 PM Hernan Wilkinson <
> hernan.wilkinson at 10pines.com> wrote:
>
>>
>> Thanks Clément! it worked perfectly!
>> I did not know about the externalize/internalize stuff, I saw them
>> everywhere but I did not understand it :-)
>> I there documentation or something to read about those kind of things?
>>
>> Thanks!
>> Hernan
>>
>> On Mon, Oct 8, 2018 at 4:12 PM Clément Béra <bera.clement at gmail.com>
>> wrote:
>>
>>>
>>> Hi,
>>>
>>> I think the general idea is that only the methods inlined in interpret
>>> can use localSP/localFP which are mapped to registers but only in the
>>> interpret method to make the interpreter quicker. In the rest of the code
>>> you need to used framePointer/stackPointer. Getting out of inlining in the
>>> interpreter requires a call to a method such as externalizeFPandSP which
>>> moves from the registers the value to variables, and internalizeIPandSP
>>> does the other way around.
>>>
>>> So in your case you need to see if for interpreter performance you want
>>> your code to be inlined if the main interpreter loop, if so, then use
>>> localSP, else, use stackPointer.
>>>
>>> Hope this helps!
>>>
>>> Best!
>>>
>>>
>>> On Mon, Oct 8, 2018 at 8:51 PM Hernan Wilkinson <
>>> hernan.wilkinson at 10pines.com> wrote:
>>>
>>>>
>>>> Hi,
>>>>  In the implementation of the dynamically typed vm I'm doing (to give
>>>> it a name) I need to get the parameters when a method gets activated.
>>>>  To do it I implemented a not-inlined method that sends the message
>>>> #internalStackValue:
>>>>  The problem is that the code for that method is not generated. The
>>>> method gets removed from the methods to generate code because it access
>>>> "localSP" although not directly but due to inlining #internalStackValue:
>>>>
>>>>  How should I access the arguments then? Why I can not use "localSP"?
>>>>
>>>>  The method source is:
>>>> keepArgumentTypes
>>>>
>>>> <inline: false>
>>>> | additionalMethodState tempVarsTypes |
>>>> additionalMethodState := self additionalMethodStateOf: newMethod.
>>>> additionalMethodState = objectMemory nilObject ifTrue: [ ^self ].
>>>> tempVarsTypes := objectMemory followObjField: 2 ofObject:
>>>> additionalMethodState.
>>>> tempVarsTypes = objectMemory nilObject ifTrue: [ ^self ].
>>>> 0 to: argumentCount-1 do: [ :argIndex |
>>>> self keepTypeInformationIn: tempVarsTypes at: argIndex for: (self
>>>> internalStackValue: argIndex) ].
>>>>  I manage to solve the problem passing localSP as parameter and doing
>>>> the following, but I should not be doing that:
>>>> keepArgumentTypes: sp
>>>>
>>>> <inline: false>
>>>> | additionalMethodState tempVarsTypes |
>>>> additionalMethodState := self additionalMethodStateOf: newMethod.
>>>> additionalMethodState = objectMemory nilObject ifTrue: [ ^self ].
>>>> tempVarsTypes := objectMemory followObjField: 2 ofObject:
>>>> additionalMethodState.
>>>> tempVarsTypes = objectMemory nilObject ifTrue: [ ^self ].
>>>> 0 to: argumentCount-1 do: [ :argIndex |
>>>> self keepTypeInformationIn: tempVarsTypes at: argIndex for: (stackPages
>>>> longAtPointer: sp + (argIndex * objectMemory bytesPerOop)) ].
>>>>
>>>> --
>>>>
>>>> *Hernán WilkinsonAgile Software Development, Teaching & Coaching*
>>>> *Phone: +54-011*-4893-2057
>>>> *Twitter: @HernanWilkinson*
>>>> *site: http://www.10Pines.com <http://www.10pines.com/>*
>>>> Address: Alem 896, Floor 6, Buenos Aires, Argentina
>>>>
>>>
>>>
>>> --
>>> Clément Béra
>>> https://clementbera.github.io/
>>> https://clementbera.wordpress.com/
>>>
>>
>>
>> --
>>
>> *Hernán WilkinsonAgile Software Development, Teaching & Coaching*
>> *Phone: +54-011*-4893-2057
>> *Twitter: @HernanWilkinson*
>> *site: http://www.10Pines.com <http://www.10pines.com/>*
>> Address: Alem 896, Floor 6, Buenos Aires, Argentina
>>
>
>
> --
> Clément Béra
> https://clementbera.github.io/
> https://clementbera.wordpress.com/
>


-- 

*Hernán WilkinsonAgile Software Development, Teaching & Coaching*
*Phone: +54-011*-4893-2057
*Twitter: @HernanWilkinson*
*site: http://www.10Pines.com <http://www.10pines.com/>*
Address: Alem 896, Floor 6, Buenos Aires, Argentina
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