[perl #127999] Slowdown in split + list assign

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This is a bug report for perl from sschoeling@linet-services.de,
generated with the help of perlbug 1.40 running under perl 5.24.0.


-----------------------------------------------------------------
[Please describe your issue here]

The following snippet loses about 20% speed from 5.22.0 to 5.24.0RC1:

  my @a = ((split //, "1"x100), "-");

I can't find anything in the changes that is likely to cause this. Some
variations with the first line taken out of the Benchmark sub:

my $s = "1"x100;
my @a = ((split //, $s), "-");    # same problem

my $s = "1"x100;
my @a = ("-", split //, $s);      # same problem

my @b = split //, "1"x100;
my @a = ("-", @b)                # OK

my @b = split //, "1"x100;
my @a = (@b, "-")                # OK

my @a = ("-"); push @a, split //, "1"x100;       # OK

my @a = split //, "1"x100; push @a, "-";         # OK


Feel free to close if this is an obvious consequence of something I wasn't
aware of.


[Please do not change anything below this line]
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---
Flags:
    category=core
    severity=low
---
Site configuration information for perl 5.24.0:

Configured by sschoeling at Thu Apr 14 11:29:43 CEST 2016.

Summary of my perl5 (revision 5 version 24 subversion 0) configuration:
  Commit id: b31d1ef1144adb563cad5228eb7a7a4866b19a50
  Platform:
    osname=linux, osvers=3.13.0-83-generic, archname=x86_64-linux
    uname='linux plum-chiew 3.13.0-83-generic #127-ubuntu smp fri mar 11 00:25:37 utc 2016 x86_64 x86_64 x86_64 gnulinux '
    config_args=''
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.8.4', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678, doublekind=3
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16, longdblkind=3
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/4.8/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
    libs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.19.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.19'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector'

Locally applied patches:
    RC1

---
@INC for perl 5.24.0:
    /home/sschoeling/lib/perl5/site_perl/5.24.0/x86_64-linux
    /home/sschoeling/lib/perl5/site_perl/5.24.0
    /home/sschoeling/lib/perl5/5.24.0/x86_64-linux
    /home/sschoeling/lib/perl5/5.24.0
    /home/sschoeling/lib/perl5/site_perl/5.22.0
    /home/sschoeling/lib/perl5/site_perl/5.21.11
    /home/sschoeling/lib/perl5/site_perl/5.19.11
    /home/sschoeling/lib/perl5/site_perl/5.18.0
    /home/sschoeling/lib/perl5/site_perl/5.16.0
    /home/sschoeling/lib/perl5/site_perl/5.15.7
    /home/sschoeling/lib/perl5/site_perl/5.12.2
    /home/sschoeling/lib/perl5/site_perl
    .

---
Environment for perl 5.24.0:
    HOME=/home/sschoeling
    LANG=en_US.UTF-8
    LANGUAGE=en_US
    LC_ADDRESS=de_DE.UTF-8
    LC_IDENTIFICATION=de_DE.UTF-8
    LC_MEASUREMENT=de_DE.UTF-8
    LC_MONETARY=de_DE.UTF-8
    LC_NAME=de_DE.UTF-8
    LC_NUMERIC=de_DE.UTF-8
    LC_PAPER=de_DE.UTF-8
    LC_TELEPHONE=de_DE.UTF-8
    LC_TIME=de_DE.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/opt/sschoeling/perlbrew/bin:/home/sschoeling/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
    PERLBREW_BASHRC_VERSION=0.66
    PERLBREW_HOME=/home/sschoeling/.perlbrew
    PERLBREW_ROOT=/opt/sschoeling/perlbrew
    PERL_BADLANG (unset)
    SHELL=/bin/bash

• [perl #127999] Slowdown in split + list assign by James E Keenan via RT
• [perl #127999] Slowdown in split + list assign by perlbug-followup
• Re: [perl #127999] Slowdown in split + list assign by Dave Mitchell
• Re: [perl #127999] Slowdown in split + list assign by Dave Mitchell
• [perl #127999] Slowdown in split + list assign by Father Chrysostomos via RT
• [perl #127999] Slowdown in split + list assign by Father Chrysostomos via RT
• Re: [perl #127999] Slowdown in split + list assign by Ricardo Signes
• Re: [perl #127999] Slowdown in split + list assign by Dave Mitchell
• [perl #127999] Slowdown in split + list assign by Father Chrysostomos via RT
• Re: [perl #127999] Slowdown in split + list assign by Sven Schöling
• [perl #127999] Slowdown in split + list assign by James E Keenan via RT
• [perl #127999] Slowdown in split + list assign by Father Chrysostomos via RT