A much more limited form of WPO is still possible without LTO, as examplified by GCC's switch. This mode makes GCC assume that the module being compiled contains the entry point (usually ) of the entire program, so that every other function in it is not externally used and can be safely optimized away. Since it only applies to one module only, it cannot truly encompass the whole program. (It can be combined with LTO in the one-big-module sense, useful when the linker is not communicating back to GCC about what entry points or symbols are being used externally.)