It's not particularly a regression. Perl suffers from a particular over-arching bug, which is hard to fix (which is why it hasn't been fixed yet): elements on perl's execution stack are not reference counted. This means that if you empty something like an array whose elements are on the stack (and will have been aliased to elements of @_ if this is a function call), and if nothing else holds a reference count to those elements, then they will be prematurely freed (and possibly re-allocated) while still accessible.

That commit merely causes that bug to show up where previously it happened to be masked. For example in 5.22.0 with this code: 

my @a=(3,4);

sub x {
  @a = ();
  print "[$_]" for @_;
  print "\n";
}

x(@a);

[download]
you get: 
$ perl5220 -w ~/tmp/p
Use of uninitialized value $_ in concatenation (.) or string at /home/
+davem/tmp/p line 9.
Use of uninitialized value $_ in concatenation (.) or string at /home/
+davem/tmp/p line 9.
[][]

[download]

Dave.

In reply to Re^3: How come @_ gets changed here? by dave_the_m
in thread How come @_ gets changed here? by pritesh_ugrankar

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.