[Bug c++/49021] New: [4.6 regression] BOOST_FOREACH over vector segfaults at runtime

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49021

           Summary: [4.6 regression] BOOST_FOREACH over vector segfaults
                    at runtime
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: mikpe@it.uu.se


The following test case, which I'll also attach, segfaults at runtime when
compiled by gcc-4.6-20110513 on x86_64-linux or i686-linux.  When compiled by
gcc-4.5-20110512 it works as expected.

> cat comm-bug-test.cc 
#include <boost/foreach.hpp>
#include <vector>
#include <stdio.h>

std::vector<int> v;

std::vector<int> x;

const inline std::vector<int *>
getv()
{
    const size_t num_accesses(x.size());
    std::vector<int *> ret(num_accesses);
    for (size_t i = 0; i < num_accesses; i++)
        ret[i] = &v[x[i]];
    return ret;
}

int
main(int argc, char **argv)
{
    x.push_back(0);
    x.push_back(1);
    x.push_back(2);
    x.push_back(3);
    x.push_back(4);
    x.push_back(5);

    v.push_back(11);
    v.push_back(12);
    v.push_back(13);
    v.push_back(14);
    v.push_back(15);
    v.push_back(16);

    BOOST_FOREACH(int *w, getv())
        printf("%d\n", *w);

    return 0;
}
> /mnt/misc/install45/bin/g++ -O2 -Wall comm-bug-test.cc; ./a.out
11
12
13
14
15
16
> /mnt/misc/install46/bin/g++ -O2 -Wall comm-bug-test.cc; ./a.out
Segmentation fault
> /mnt/misc/install46/bin/g++ -v
Using built-in specs.
COLLECT_GCC=/mnt/misc/install46/bin/g++
COLLECT_LTO_WRAPPER=/mnt/misc/install46/libexec/gcc/x86_64-unknown-linux-gnu/4.6.1/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /mnt/misc/gcc-4.6-20110513/configure
--prefix=/mnt/misc/install46 --with-gmp=/home/mikpe/pkgs/linux-x86_64/gmp-4.3.2
--with-mpfr=/home/mikpe/pkgs/linux-x86_64/mpfr-2.4.2
--with-mpc=/home/mikpe/pkgs/linux-x86_64/mpc-0.8.2 --disable-plugin
--disable-lto --disable-nls --disable-libmudflap --enable-threads=posix
--enable-checking=release
--enable-languages=c,c++,objc,obj-c++,fortran,java,ada
Thread model: posix
gcc version 4.6.1 20110513 (prerelease) (GCC)

Initially found by a colleague when testing our code on Fedora 15 with Red
Hat's gcc-4.6.0 (20110428) and boost 1.46.  I then confirmed the bug on Fedora
13 with a self-compiled gcc-4.6-20110513 and boost-1.41.  -m32 or -m64 makes no
difference.