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[perl #123722] Dumper screws up aliasing of array elements

February 3, 2015 11:41
[perl #123722] Dumper screws up aliasing of array elements
Message ID:
# New Ticket Created by  Zefram 
# Please include the string:  [perl #123722]
# in the subject line of all future correspondence about this issue. 
# <URL: >

This is a bug report for perl from,
generated with the help of perlbug 1.39 running under perl 5.18.2.

[Please describe your issue here]

Setting the Purity option is supposed to make Dumper emit correct
evalable code.  For example, it makes all the difference in this case:

$ perl -MData::Dumper=Dumper -we '@a=(3,0); $a[1] = \$a[0]; print Dumper \@a'
$VAR1 = [
$ perl -MData::Dumper=Dumper -we '$Data::Dumper::Purity=1; @a=(3,0); $a[1] = \$a[0]; print Dumper \@a'               
$VAR1 = [
          do{my $o}
$VAR1->[1] = \$VAR1->[0];

But if I put the same array elements the other way round, Dumper gets
it wrong even with the Purity option:

$ perl -MData::Dumper=Dumper -we '$Data::Dumper::Purity=1; @a=(0,3); $a[0] = \$a[1]; print Dumper \@a'               
$VAR1 = [

The mention of $VAR1->[0] comes too early, before $VAR1 has been set to
an array ref, and the expression for $VAR1->[1] doesn't account for the
copying performed by the [...] array constructor.  Correct output would
have to be much like the correct output for the first array:

$VAR1 = [
          do{my $o},
$VAR1->[0] = \$VAR1->[1];

[Please do not change anything below this line]
Site configuration information for perl 5.18.2:

Configured by root at Wed Mar 26 14:32:51 UTC 2014.

Summary of my perl5 (revision 5 version 18 subversion 2) configuration:
    osname=linux, osvers=3.2.0-4-amd64, archname=x86_64-linux-ld
    uname='linux ukmcwzefram.photobox.priv 3.2.0-4-amd64 #1 smp debian 3.2.54-2 x86_64 gnulinux '
    config_args='-des -Duseshrplib -Duse64bitint -Duselongdouble -Uusethreads -Uusemultiplicity -Dprefix=/opt/perl-5.18.2 -Dsiteprefix=/opt/perl-5.18.2 -Dvendorprefix=/opt/perl-5.18.2/vendor -Doptimize=-ggdb -O3 -fbranch-target-load-optimize -fgcse-las -fgcse-sm -fipa-pta -floop-block -floop-interchange -floop-strip-mine -fmodulo-sched -fomit-frame-pointer -freorder-blocks-and-partition -fsched-spec-load -fsched-spec-load-dangerous -ftree-loop-distribution -Dcccdlflags=-fPIC -O3 -pipe'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=define, use64bitall=define, uselongdouble=define
    usemymalloc=n, bincompat5005=undef
    cc='cc', ccflags ='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-ggdb -O3 -fbranch-target-load-optimize -fgcse-las -fgcse-sm -fipa-pta -floop-block -floop-interchange -floop-strip-mine -fmodulo-sched -fomit-frame-pointer -freorder-blocks-and-partition -fsched-spec-load -fsched-spec-load-dangerous -ftree-loop-distribution',
    cppflags='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.7.2', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
    ivtype='long', ivsize=8, nvtype='long double', nvsize=16, Off_t='off_t', lseeksize=8
    alignbytes=16, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib /usr/lib
    libs=-lnsl -ldb -ldl -lm -lcrypt -lutil -lc
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc
    libc=, so=so, useshrplib=true,
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E -Wl,-rpath,/opt/perl-5.18.2/lib/5.18.2/x86_64-linux-ld/CORE'
    cccdlflags='-fPIC -O3 -pipe', lddlflags='-shared -ggdb -O3 -fbranch-target-load-optimize -fgcse-las -fgcse-sm -fipa-pta -floop-block -floop-interchange -floop-strip-mine -fmodulo-sched -fomit-frame-pointer -freorder-blocks-and-partition -fsched-spec-load -fsched-spec-load-dangerous -ftree-loop-distribution -L/usr/local/lib -fstack-protector'

Locally applied patches:

@INC for perl 5.18.2:

Environment for perl 5.18.2:
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PERL_BADLANG (unset)
    SHELL=/usr/bin/zsh Perl Programming lists via nntp and http.
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