parrot puts an invalid value in a register when vtable override does not return as expected

[NotFound]

This shows the problem:

$ cat override.pir
.sub main
    $P0 = newclass ['Foo']
    $P1 = new $P0
    $P2 = $P1[0]
    say 'in main'
    print $P2
.end

.namespace [ 'Foo' ]

.sub get_pmc_keyed_int :vtable
    .param int i
    say 'Foo overrides'
.end
$ parrot override.pir
Foo overrides
in main
Segmentation fault (core dumped)

Oddly, it doesn't segfault in a non optimized build.

[jkeenan]

Additional testing data:

On Linux/i386, configured with --optimize, I get the same segfault as reported by NotFound.

On Linux/i386, configured without --optimize, I get:

Foo overrides
in main
P

... i.e., an unexpected P (with no newline following).

On Darwin/PPC, configured without --optimize, I get the desired results:

./parrot override.pir 
Foo overrides
in main

All tests run at r46014.

kid51

[NotFound]

The problem seems to be that the call to the vtable override does not fill the ->P result when there is no .return, and random garbage in the local variable is returned.

Worked around in r46482 by initializing the "result" local variable with PMCNULL.

[NotFound]

Added a reference to this ticket in the regression test in r47647. Closing.