Handwritten ASM for perf is almost never worth it in modern times. C compiled with GCC/Clang will almost always be just as fast or faster. You might use some inline ASM to use a specific instruction if the compiler doesn't support generating it yet (like AVX512 or AES), but even for that there's probably an intrinsic available. You can still inspect the output to make sure it's not doing anything stupid.

Plus it's C so it's infinitely more maintainable and way more portable.