A lot of real-world projects turn off strict aliasing, such as the Linux kernel. It is just too difficult to think about every possible issue that could happen

A lot of real-world projects turn off strict aliasing, such as the Linux kernel. It is just too difficult to think about every possible issue that could happen when doing a typecast. Autovectorization doesn't tend to work well anyway. In most cases where it truly matters, people use inline assembly... for example, in CRC calculations code, tight inner loops in math libraries, etc. If you really want autovectorization, "restrict" is a better solution which doesn't require breaking the world to implement.