There are degrees to "assembly". There's .s source files. There is inline assembly with varying degrees of compiler plumbing/spilling/automation. There are intr

There are degrees to "assembly". There's .s source files. There is inline assembly with varying degrees of compiler plumbing/spilling/automation. There are intrinsics where you delegate register allocation to the compiler and allow it to optimize if it can. Then, sometimes you write specific C idioms that you know LLVM is going to turn into certain instructions. For highest performance, you will always think in assembly, and in fact in the internals of your target CPU (as far as they are known), even if you have various layers of software to produce the bitstream in your object files.