It's just like the compiler vs assembly language arguments back in the 1970s to mid 80s. Yes, you can get better results with hand-coding the RTL, and indeed w

It's just like the compiler vs assembly language arguments back in the 1970s to mid 80s. Yes, you can get better results with hand-coding the RTL, and indeed with hand-placing the resulting transistors and even making them different sizes depending on the fan-out required etc. The question is: can you AFFORD to? SiFive use Chisel to design all their CPUs. Their original 32 bit FE310 back in late 2016 ran at 320 MHz on a 180nm process -- absolutely killing the frequencies ARM Cortex M3/M4 were available in at the time (or now .. 180 MHz is still the fastest I'm aware of) SiFive's FU540 with quad core U54 64 bit cores ran at 1.5 GHz on a 28nm process in early 2018, as do the quad dual-issue U74 cores in their FU740 this year. Sure, you can do better with hand design, but it costs $billions. Only Intel, AMD, and Apple have that kind of money to spend.