The problem is that dynamic linking is the norm. If you're writing a specific application, that's one thing. But if you're writing some random C++ library the

The problem is that dynamic linking is the norm. If you're writing a specific application, that's one thing. But if you're writing some random C++ library then you usually have no idea whether it will be compiled into an executable or a shared library. If TLS is slow in either of those cases, then the only solution is to not use TLS at all.