Hubička: Link time and inter-procedural optimization improvements in GCC 5

Jan HubiAka has posted a lengthydiscussion of the optimization improvements found in the upcomingGCC 5.0 release. "Identical code folding is a new pass(contributed by Martin LiAka, SUSE) looking for functions with the samecode and variables with the same constructors. If some are found, one copyis removed and replaced one by an alias to another where possible. This isespecially important for C++ code bases that tend to contain duplicatedfunctions as a result of template instantiations."