thawed subs with :vtable don't register properly for existing classes

[jhorwitz]

If a class is created before load_bytecode thaws a :vtable sub for that class, parrot tries to override a vtable method with the same name as the thawed sub. This blows up when the sub name is not a valid vtable function, which is common in Rakudo. Everything works in fine in pure PIR.

At first glance, the culprit appears to be add_vtable_override() in src/pmc/class.pmc, which only uses the sub's name to check if it's a valid override. Shouldn't it also check the thawed sub's vtable_index?

This breaks mod_perl6, as mod_parrot needs to load P6object before loading Rakudo's perl6.pbc.

Test case follows.

bar.pir:

.sub '__onload' :load
    $P0 = newclass ['Bar']
.end

foo.pir:

.sub '__onload' :init
    load_bytecode 'bar.pbc'
.end

.namespace ['Bar']

.sub 'invalidname' :vtable('get_string') :method
    $S0 = 'hello world'
    .return($S0)
.end

baz.pir:

.sub main :main
    load_bytecode 'bar.pbc'
    load_bytecode 'foo.pbc'
.end

Output:

[jeff@groovy parrot]$ ./parrot -o foo.pbc foo.pir
[jeff@groovy parrot]$ ./parrot -o bar.pbc bar.pir
[jeff@groovy parrot]$ ./parrot baz1.pir
'invalidname' is not a valid vtable function name.
current instr.: 'main' pc 2 (baz1.pir:3)