Newbie code segfaults

[p6rt]

Migrated from rt.perl.org#127748 (status was 'resolved')

Searchable as RT127748$

[p6rt]

From @lizmat

==========================
my $a = 14;
while (True) {
  my $z = (2..13).first(-> $x { !($a %% $x) });
  last if (!$z);
  $a += 14
}
say $a

The above code “verbatim” segfaults on OS X and Linux on HEAD.

Replacing either the (True) by True, or (!$z) by !$z, or adding an additional say after the loop, will make the code succeed.

Looking at the output of —target=optimize between (!$z) and !$z, I see only this significant difference​:

- - QAST​::Op(callstatic &prefix​:<!>) :BY<modifier_expr W> :statement_id<?> :WANTED !
+ - QAST​::Op(callstatic &prefix​:<!>) :BY<modifier_expr W> :WANTED !

I would have sorta expected that the () would not make a difference for the generated code at all, but apparently it does?

Also, disabling spesh or JIT does not seem to make a difference.

In any case, I thought this would be a nice thing for the right people. :-)

Discussion at​: http://irclog.perlgeek.de/perl6/2016-03-20#i_12212186

Liz

[p6rt]

From @lizmat

On 20 Mar 2016, at 14​:39, Elizabeth Mattijsen (via RT) <perl6-bugs-followup@​perl.org> wrote​:

# New Ticket Created by Elizabeth Mattijsen
# Please include the string​: [perl #​127748]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl6/Ticket/Display.html?id=127748 >

==========================
my $a = 14;
while (True) {
my $z = (2..13).first(-> $x { !($a %% $x) });
last if (!$z);
$a += 14
}
say $a

Some more datapoints​:

Changing the first block to

  { !($a %% $^x) }

does *not* fix the issue, changing the block to

  { !($a %% $_) }

*does* fix the issue.

Also, changing the type of $a to​:

  my Int $a = 14;

does *not* fix the issue, whereas changing it to​:

  my int $a = 14;

*does* fix the issue.

Liz

[p6rt]

From @jnthn

On Sun Mar 20 06​:39​:39 2016, elizabeth wrote​:

==========================
my $a = 14;
while (True) {
my $z = (2..13).first(-> $x { !($a %% $x) });
last if (!$z);
$a += 14
}
say $a

The above code “verbatim” segfaults on OS X and Linux on HEAD.

Replacing either the (True) by True, or (!$z) by !$z, or adding an
additional say after the loop, will make the code succeed.

Looking at the output of —target=optimize between (!$z) and !$z, I see
only this significant difference​:

- - QAST​::Op(callstatic &prefix​:<!>) :BY<modifier_expr W>
:statement_id<?> :WANTED !
+ - QAST​::Op(callstatic &prefix​:<!>) :BY<modifier_expr W> :WANTED !

I would have sorta expected that the () would not make a difference
for the generated code at all, but apparently it does?

Also, disabling spesh or JIT does not seem to make a difference.

In any case, I thought this would be a nice thing for the right
people. :-)

Discussion at​: http://irclog.perlgeek.de/perl6/2016-03-20#i_12212186

Was a GC invariant violation that occasionally led to memory corruption (thus why it was easy to make it vanish with silly changes). Actually a regression within the last month or two. Fixed it, and add a test to integration/weird-errors.t.

/jnthn

[p6rt]

The RT System itself - Status changed from 'new' to 'open'

[p6rt]

@jnthn - Status changed from 'open' to 'resolved'