ub-icf

foo.c

const char * const string;
static char *handle;

void foo()
{
	xxx(handle);
}

gistfile1.txt

$ gcc -O2 -c -o foo.o foo.c && nm foo.o
0000000000000000 T foo
0000000000000000 b handle
0000000000000000 B string
                 U xxx
                 
$ gcc -O2 -fno-ipa-icf -c -o foo.o foo.c && nm foo.o
0000000000000000 T foo
0000000000000008 C string
                 U xxx

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /build/gcc/src/gcc-5.1.0/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 --with-isl --enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object --enable-linker-build-id --enable-lto --enable-plugin --enable-install-libiberty --with-linker-hash-style=gnu --enable-gnu-indirect-function --disable-multilib --disable-werror --enable-checking=release --with-default-libstdcxx-abi=c++98
Thread model: posix
gcc version 5.1.0 (GCC)