I would've assumed glibc has a bunch of different implementations and then picks the fastest one at runtime depending on CPU capabilities, but maybe they just s

I would've assumed glibc has a bunch of different implementations and then picks the fastest one at runtime depending on CPU capabilities, but maybe they just scrapped that since GCC has built-in versions of most string functions anyways, since it can often know or at least guess the characteristics of the input and output (length, alignment) and emit different code depending on that.