[Accidentally posted to Google Groups first]
I'm finally doing some work on Leo's PIR Z-machine interpreter. (I've
added about 15 opcodes to the 10 or so he started with. Luckily, he did
a lot of the infrastructure stuff that scared me as a PIR newbie. The
tester I wrote while developing Plotz passes 85 tests. Mostly.)
The compiler translates Z-code into PIR, then compiles and runs it. The
image of the Z-file (where the Z-machine stores its global variables
and other useful things) is stored in a global called Image. So if you
need to access one of the Z-machine's global variables, you emit code
like:
.local pmc image
image = global 'Image'
.GET_WORD($I181 , image, 692)
where the last line is a macro that pulls the global variable out of
the Z-machine memory. But Leo was smart and, while translating, says to
only load image (i.e. to only output the first two lines) once per
Z-code subroutine.
Now here's the problem. My Z-code emitted code like this:
if $I17 == 3 goto L1234
.local pmc image
image = global 'Image'
.GET_WORD($I181 , image, 692)
L1234:
print "yes, blah"
.GET_WORD($I182 , image, 692)
If $I17==3, then when we get to the second GET_WORD we exit with an
error because we don't know what image is.
So I think to avoid these problems I need to declare image at the top
of every Z-code sub. My question is, is there any cost associated with
always declaring this array holding 50-500K ints, other than having one
P register always full? Since everything else in the translated code is
integers & strings I'm not really worried about filling my P registers.
The only other option I can think of is keeping track of how my scopes
are nesting while translating, which sounds like a disaster.
This is what I get for trying to develop in PIR after ignoring the
mailing list for 6 months and not reading the basic docs.
Thanks,
-Amir Karger
It's better to write me at [EMAIL PROTECTED]
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