[Bug c++/49339] New: [C++0x][lambda][unused-parameter]g++ reports unused parameter even it's referenced in function

[lene13 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49339

           Summary: [C++0x][lambda][unused-parameter]g++ reports unused
                    parameter even it's referenced in function
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: len...@gmail.com


I'm using ArchLinux with GCC 4.6.0 (20110603).
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-pc-linux-gnu/4.6.0/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: /build/src/gcc-4.6-20110603/configure --prefix=/usr
--libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared
--enable-threads=posix --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-clocale=gnu --enable-gnu-unique-object
--enable-linker-build-id --with-ppl --enable-cloog-backend=isl --enable-lto
--enable-gold --enable-ld=default --enable-plugin --with-plugin-ld=ld.gold
--disable-multilib --disable-libstdcxx-pch --enable-checking=release
Thread model: posix
gcc version 4.6.0 20110603 (prerelease) (GCC)

When compiling following codes

#include <algorithm>
#include <vector>
#include <memory>
#include <iostream>

template <typename _RawType>
void append(std::vector<_RawType>& former, std::vector<_RawType>&& latter)
{
    std::for_each(latter.begin()
                , latter.end()
                , [&](_RawType& x)
                  {
                      former.push_back(std::move(x));
                  });
}

int main(void)
{
    std::vector<int> aa;
    append(aa, std::vector<int>());
    return 0;
}

with

g++ % -Wunused-parameter -std=c++0x

g++ prints

unused-param.cpp: In instantiation of ‘append(std::vector<_RealType>&,
std::vector<_RealType>&&) [with _RawType = int]::<lambda(int&)>’:
unused-param.cpp:9:5:   instantiated from ‘void append(std::vector<_RealType>&,
std::vector<_RealType>&&) [with _RawType = int]’
unused-param.cpp:20:34:   instantiated from here
unused-param.cpp:11:34: warning: unused parameter ‘x’ [-Wunused-parameter]

but `x` is referenced in line 13 ("former.push_back(std::move(x));").