There was probably just one single bottleneck that got fixed by the ASM code. Often in my experience, not enough work is done to identify what the bottleneck is

There was probably just one single bottleneck that got fixed by the ASM code. Often in my experience, not enough work is done to identify what the bottleneck is before trying to solve performance. It's not like every line of C takes N amount of time and every line of ASM takes a fraction of N. Most lines of C compile to the optimal ASM right off the bat. If this was one of those case like 90% of cases are, where you just need to identify the bottleneck, you can normally fix it and stay in C (not ASM), although I used to enjoy doing some inline ASM in my C code to milk out every last bit of performance in critical loops.