[Bug c++/54276] New: Lambda in a Template Function Undefined Reference to local static

["travis at gockelhut dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54276

             Bug #: 54276
           Summary: Lambda in a Template Function Undefined Reference to
                    local static
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: travis@gockelhut.com


Created attachment 28021
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28021
Compile

The following code will fail to link with "undefined reference to `x'" when
compiled with g++ (4.6.1, 4.6.2, 4.6.3 and 4.7.0):

    template <typename T>
    void foo(T)
    {
        static int x = 1;
        auto f = [] { return x + 1; };
        f();
    }

---

    /tmp/cc236Klq.o: In function `void
foo<int>(int)::{lambda()#1}::operator()() const':
    unmangled-ref.cpp:(.text+0x20): undefined reference to `x'
    collect2: error: ld returned 1 exit status

---

It *appears* we attempt to load x from the unmangled version:

    movl    _ZL1x(%rip), %eax

In g++ 4.6.3, you can work around this issue by explicitly capturing the static
variable:

    auto f = [&x] { return x + 1; };

So x is loaded from the fully-mangled name:

    movq    $_ZZ3fooIiEvT_E1x, -16(%rbp)

---

$> g++ -v
Using built-in specs.
COLLECT_GCC=g++-4.7
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.7/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.7.0-7ubuntu3' --with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs
--enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.7 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7
--libdir=/usr/lib --enable-nls --disable-bootstrap --with-sysroot=/
--enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes
--enable-gnu-unique-object --enable-plugin --enable-objc-gc --disable-werror
--with-arch-32=i686 --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.7.0 (Ubuntu/Linaro 4.7.0-7ubuntu3)