Intrinsics are compatible across compilers and OSs within the same architecture, and are also mostly compatible between 32 and 64 bit variants of the same archi

Intrinsics are compatible across compilers and OSs within the same architecture, and are also mostly compatible between 32 and 64 bit variants of the same architecture. With asm, you have to handle the 3 different calling conventions between x86, x86-64, and win64, and also write two completely separate implementations for arm32 and arm64, instead of just one x86 intrinsic and one NEON intrinsic version. Sure ffmpeg tries to automatically handle the different x86 calling conventions with standard macros, but there's still some %if WIN64 scattered around, and 32-bit x86's register constraints means larger functions are littered with %if ARCH_X86_64. Which brings us to the most "more effort" of assembly - no variables or inline functions, only registers and macros. Which is okay for self-contained functions a hundred lines or so, but less so with heavily templated multi-thousand line files of deeply intertwined macros nested 4 levels deep. Being able to write an inlined function that has no side effects felt a thousand lines away reduces mental effort by a lot, as does not having to redo register allocation across a thousand lines because you now need another temporary register for a short section of code, or even think about it much in the first place to still get near-optimal performance on modern CPUs.