Symbolic vs Named variable register allocation

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Pete Lomax

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Dec 3, 2003, 7:58:53 AM12/3/03
to perl6-i...@perl.org
The following demonstrates that $I1 and .local int i map to the same
register in the output pasm code:

.sub _main
goto L1
test:
$I1 = 1
ret
L1:
.local int i
i = 2
call test
print i # prints 1, not 2
end
.end

parrot -o - t.imc shows:
_main:
branch L1
test:
set I16, 1
ret
L1:
set I16, 2
bsr test
print I16
end


Is this a bug, or am I missing something?

Pete
PS this happens on pow builds 0.0.11 (20/09/03), and 15/11/03
Pete
http://palacebuilders.pwp.blueyonder.co.uk/euphoria.html

Leopold Toetsch

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Dec 3, 2003, 9:01:00 AM12/3/03
to Pete Lomax, perl6-i...@perl.org
Pete Lomax <pete...@blueyonder.co.uk> wrote:
> The following demonstrates that $I1 and .local int i map to the same
> register in the output pasm code:

Yep. The problem seems to be the backward branch. When you put the
"test" sub after the "end" op, its working fine.

leo

Melvin Smith

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Dec 3, 2003, 9:35:26 AM12/3/03
to l...@toetsch.at, Pete Lomax, perl6-i...@perl.org

At quick glance I would guess IMCC assumes that the "call test" branches
to a basic block that doesn't overlap with the callee basic block.

Much (most) of the flow analysis code was done before we adopted
new calling conventions. I'll have a look to see if there a quick fix
that would allow the code snippet sample to be legal.

-Melvin


Pete Lomax

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Dec 10, 2003, 10:54:00 AM12/10/03
to perl6-i...@perl.org
>At 03:01 PM 12/3/2003 +0100, Leopold Toetsch wrote:
>>Pete Lomax <pete...@blueyonder.co.uk> wrote:
>> > The following demonstrates that $I1 and .local int i map to the same
>> > register in the output pasm code:
>>
>>Yep. The problem seems to be the backward branch. When you put the
>>"test" sub after the "end" op, its working fine.
>
Just a quick comment inspired by reading the perl 6 summary:

As Leo said, it is backward branch. $I1 and $I2 can both get stored in
the same register, as can .local int i and .local int j. I'm just
pointing out that my subject line was a little misleading.

Pete

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