Rakudo segfault, goes away if MVM_SPESH_OSR_DISABLE=1

segfault-on-write-bytes.txt

The error occurs with the call to crc32, from this line in Image::PNG::Portable:

$fh.write: bytes String::CRC32::crc32 @td;

After removing .race from the calling program, can further localize to this line in routine crc32:

$crc +^= 0xFFFFFFFF

================================================================================================
This is Rakudo Perl 6 running in the GNU debugger, which often allows the user to generate useful back-
traces to debug or report issues in Rakudo, the MoarVM backend or the currently running code.

This Rakudo version is 2018.10.29.g.052067.fd.1 built on MoarVM version 2018.10.26.g.318.e.1.ec.55,
running on macosx (10.11.6) / darwin (15.6.0)

Type `bt full` to generate a backtrace if applicable, type `q` to quit or `help` for help.
------------------------------------------------------------------------------------------------
Reading symbols from /Users/dhoekman/.rakudobrew/moar-master/install/bin/moar...(no debugging symbols found)...done.
Starting program: /Users/dhoekman/.rakudobrew/moar-master/install/bin/moar --execname=/Users/dhoekman/.rakudobrew/bin/../moar-master/install/bin/perl6-gdb-m --libpath=/Users/dhoekman/.rakudobrew/moar-master/install/share/nqp/lib --libpath=/Users/dhoekman/.rakudobrew/moar-master/install/share/perl6/lib --libpath=/Users/dhoekman/.rakudobrew/moar-master/install/share/perl6/runtime /Users/dhoekman/.rakudobrew/moar-master/install/share/perl6/runtime/perl6.moarvm exp/Kronecker_product_based_fractals
[New Thread 0x1217 of process 42087]
This type cannot unbox to a native integer: P6opaque, Mu
  in sub crc32 at /Users/dhoekman/.rakudobrew/moar-master/install/share/perl6/site/sources/B11DB940E55C33C6937C1A1A778565879AE880A0 (String::CRC32) line 51
  in sub write-chunk at /Users/dhoekman/.rakudobrew/moar-master/install/share/perl6/site/sources/7941A7DCDF4B308B87530EF4CA5D4019405D3297 (Image::PNG::Portable) line 83
  in method write at /Users/dhoekman/.rakudobrew/moar-master/install/share/perl6/site/sources/7941A7DCDF4B308B87530EF4CA5D4019405D3297 (Image::PNG::Portable) line 64
  in block <unit> at exp/Kronecker_product_based_fractals line 39

[Inferior 1 (process 42087) exited with code 01]


##########################################################################'
# simplest version of the program that triggers the bug
# note how only the 2nd write (of the same input) triggers the bug
# avoid actual segfault (to allow debugging) with MVM_JIT_DISABLE=1
# based on: http://rosettacode.org/wiki/Kronecker_product_based_fractals

use Image::PNG::Portable;

sub kronecker-product ( @a, @b ) { (@a X @b).map: { (.[0].list X* .[1].list).Array } }

sub kronecker-fractal ( @pattern, $order = 4 ) {
    my @kronecker = @pattern;
    @kronecker = kronecker-product(@kronecker, @pattern) for ^$order;
    @kronecker
}

my @vicsek = ( [0, 1, 0], [1, 1, 1], [0, 1, 0] );

for  'vicsek', @vicsek, 4,
     'vicsek', @vicsek, 4
  -> $name,    @shape,  $order {
    my @img = kronecker-fractal( @shape, $order );
    my $png = Image::PNG::Portable.new: :width(@img[0].elems), :height(@img.elems);
    for ^@img[0] X ^@img -> ($x, $y) {
        $png.set: $x, $y, |( @img[$y;$x] ?? <255 255 32> !! <16 16 16> );
    }
    $png.write: "run/kronecker-{$name}-perl6.png";
}