From jtobey@ne.mediaone.net

This is a bug report for perl from jtobey@​feynman.localnet,
generated with the help of perlbug 1.27 running under perl v5.5.650.

The following program unexpectedly prints "undefined"​:

  my ($x, $y);
  $z = 1;
  $x = $y = 1 + $z;
  print "undefined" unless defined $y;

This behavior affects Perl 5.00563 and 5.5.560, but not 5.00503.
It happens only if $x and $y are both declared with "my", and the
right side of the assignment is a compound expression (not just "1"
or "$z").

The deparsed output is interesting​:

  $ perl -MO=Deparse -e 'my ($x, $y); $x = $y = 1 + $z;'
  my($x, $y);
  $x = 1 + $z;
  -e syntax OK

-John

Site configuration information for perl v5.5.650​:

Configured by jtobey at Fri Feb 11 02​:13​:31 EST 2000.

Summary of my perl5 (revision 5.0 version 5 subversion 650) configuration​:
  Platform​:
  osname=linux, osvers=2.2.14pre16, archname=i686-linux
  uname='linux feynman 2.2.14pre16 #1 thu dec 23 19​:33​:36 est 1999 i686 unknown '
  config_args='-Dcc=gcc -Dprefix=/usr/local -Doptimize=-g -O2 -ders'
  hint=recommended, useposix=true, d_sigaction=define
  usethreads=undef use5005threads=undef useithreads=undef
  usesocks=undef useperlio=undef d_sfio=undef
  use64bits=undef uselargefiles=define usemultiplicity=undef
  Compiler​:
  cc='gcc', optimize='-g -O2', gccversion=2.95.2 19991109 (Debian GNU/Linux)
  cppflags='-Dbool=char -DHAS_BOOL -DDEBUGGING -fno-strict-aliasing -I/usr/local/include'
  ccflags ='-Dbool=char -DHAS_BOOL -DDEBUGGING -fno-strict-aliasing -I/usr/local/include'
  stdchar='char', d_stdstdio=define, usevfork=false
  intsize=4, longsize=4, ptrsize=4, doublesize=8
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
  alignbytes=4, usemymalloc=n, prototype=define
  Linker and Libraries​:
  ld='gcc', ldflags =' -L/usr/local/lib'
  libpth=/usr/local/lib /lib /usr/lib
  libs=-lnsl -lndbm -lgdbm -ldbm -ldb -ldl -lm -lc -lposix -lcrypt
  libc=/lib/libc-2.1.2.so, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
  cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'

Locally applied patches​:
 

@​INC for perl v5.5.650​:
  /usr/local/lib/perl5/5.5.650/i686-linux
  /usr/local/lib/perl5/5.5.650
  /usr/local/lib/perl5/site_perl/5.5.650/i686-linux
  /usr/local/lib/perl5/site_perl/5.5.650
  /usr/local/lib/perl5/site_perl/5.005/i686-linux
  /usr/local/lib/perl5/site_perl/5.005
  /usr/local/lib/perl5/site_perl
  .

Environment for perl v5.5.650​:
  HOME=/home/jtobey
  LANG (unset)
  LANGUAGE (unset)
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)
  PATH=/home/jtobey/bin​:/jtobey/local/bin​:/usr/local/bin​:/bin​:/usr/bin​:/usr/X11R6/bin​:/usr/local/sbin​:/usr/sbin​:/sbin
  PERL_BADLANG (unset)
  SHELL=/bin/bash

From [Unknown Contact. See original ticket]

John Tobey writes​:

my \($x\, $y\);
$z = 1;
$x = $y = 1 \+ $z;
print "undefined" unless defined $y;

This behavior affects Perl 5.00563 and 5.5.560, but not 5.00503.
It happens only if $x and $y are both declared with "my", and the
right side of the assignment is a compound expression (not just "1"
or "$z").

The deparsed output is interesting​:

$ perl \-MO=Deparse \-e 'my \($x\, $y\); $x = $y = 1 \+ $z;'
my\($x\, $y\);
$x = 1 \+ $z;
\-e syntax OK

Oups, the optimizer was removing the assignment *twice* for the same
operation.

Sorry,
Ilya

--- ./t/op/lex_assign.t~	Sun Jan  2 15:44:26 2000
+++ ./t/op/lex_assign.t	Fri Feb 11 17:46:25 2000
@@ -24,7 +24,7 @@ sub subb {"in s"}
 
 @INPUT = <DATA>;
 @simple_input = grep /^\s*\w+\s*\$\w+\s*[#\n]/, @INPUT;
-print "1..", (9 + @INPUT + @simple_input), "\n";
+print "1..", (10 + @INPUT + @simple_input), "\n";
 $ord = 0;
 
 sub wrn {"@_"}
@@ -95,6 +95,18 @@ print "ok $ord\n";
   print "ok $ord\n";
 
 }
+
+# Chains of assignments
+
+my ($l1, $l2, $l3, $l4);
+my $zzzz = 12;
+$zzz1 = $l1 = $l2 = $zzz2 = $l3 = $l4 = 1 + $zzzz;
+
+$ord++;
+print "# $zzz1 = $l1 = $l2 = $zzz2 = $l3 = $l4 = 13\nnot "
+  unless $zzz1 == 13 and $zzz2 == 13 and $l1 == 13
+  and $l2 == 13 and $l3 == 13 and $l4 == 13;
+print "ok $ord\n";
 
 for (@INPUT) {
   $ord++;
--- ./op.c~	Tue Feb  1 15:29:47 2000
+++ ./op.c	Fri Feb 11 17:28:53 2000
@@ -5694,7 +5694,9 @@ Perl_ck_sassign(pTHX_ OP *o)
     OP *kid = cLISTOPo->op_first;
     /* has a disposable target? */
     if ((PL_opargs[kid->op_type] & OA_TARGLEX)
-	&& !(kid->op_flags & OPf_STACKED))
+	&& !(kid->op_flags & OPf_STACKED)
+	/* Cannot steal the second time! */
+	&& !(kid->op_private & OPpTARGET_MY))
     {
 	OP *kkid = kid->op_sibling;