Depending on how you count, the ratio might not be that small. A lot of hot code are written in hand-coded inline assembly, so in terms of CPU cycles run it's probably non-negligible.

i.e. take a look at the glibc implementation of 'strcmp` [0]

[0] https://github.com/bminor/glibc/blob/master/sysdeps/x86_64/m...