[Vm-dev] StackInterp/Cog>>transferTo: - assertValidExecutionPointe:r:s differences

[Ben Coman]

On 10 June 2016 at 20:17, Eliot Miranda <eliot.miranda at gmail.com> wrote:

>
> Hi Ben,
>
>     this time I'll try and answer your question rather than my brain
> fart...
>
> > On Jun 9, 2016, at 6:46 PM, Ben Coman <btc at openinworld.com> wrote:
> >
> >
> > Just curious about the difference in instructionPointer between these
> two...
> >
> > StackInterpreter>>transferTo:
> >     self assertValidExecutionPointe: instructionPointer + 1 r:
> > framePointer s: stackPointer.
> >
> >
> > CoIntepreter>>transferTo:from:
> >    self assertValidExecutionPointe: instructionPointer r:
> > framePointer s: stackPointer.
>
> In the StackInterpreter, as in the context Interpreter the next bytecode
> is fetched by pre-incrementing the instructionPointer and then fetching the
> byte it points to.  Hence it may point to before the first bytecode and
> hence the + 1 above.  1 is subtracted from a context's pc (2 actually cuz
> pc is 1-relative and instructionPointer is 0-relative) to derive
> instructionPointer.
>
> In the Cog VM instructionPointer may also be a machine code pc. So rather
> than add one, which only makes sense for interpreted methods, the
> CoInterpreter's assertValidExecutionPointer:s: allows for the - 1 if a
> frame us interpreted.  The StackInterpreter's method predates the
> CoInterpreter.
>


I was just wandering in the vicinity of this again, and had a new query...

What is the semantic difference in the naming of the arguments (i.e. lsp<=>
lisp  and  lfp<=>lifp)
between.... ?
StackInterpreter >> assertValidExecutionPointe: lip    r: lfp    s: lsp
imbar: inInterpreter    line: ln
CoInterpreter     >> assertValidExecutionPointe: lip    r: lifp    s: lisp
 imbar: inInterpreter    line: ln

because search/replacing makes it easier to diff the two methods...
https://www.diffchecker.com/CL32EXql

This shows the StackInterpreter method refactored slightly to extract
"methodField" variable similar to the CoInterpreter
making it easier to compare the two, i.e. red-line-16 and green-line-18 are
identical,
but red-line-13 and green-line-14 set "methodField" using different
messages, which however have identical definitions.

StackInterpreter >> frameMethod: theFP
<inline: true>
<var: #theFP type: #'char *'>
^stackPages longAt: theFP + FoxMethod

CoInterpreter >> frameMethodField: theFP
<inline: true>
<var: #theFP type: #'char *'>
^stackPages longAt: theFP + FoxMethod

Would it be reasonable to change red-line-13 to send #frameMethodField:
instead?  Hopefully my slight rearrangement of the asserts in red okay.

cheers -ben
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.squeakfoundation.org/pipermail/vm-dev/attachments/20180506/fa299c39/attachment.html>