The compiler can still do optimizations on intrinsics - clang passes most through its regular optimizations, so you get things like loop unrolling, CSE (quite p

The compiler can still do optimizations on intrinsics - clang passes most through its regular optimizations, so you get things like loop unrolling, CSE (quite powerful if you have multiple invocations of the same SIMD thing, deduplicating constant loads or whatnot), and some genuine improvements/reducing what you need to pay attention to (don't need to manually merge to 'vpandn', 'vpand a,b,c; vptest a,a' → 'vptest b,c', sometimes improving shuffles, moving out negation from movmsk of negation of vpcmpeq), though it can of course make things worse too as regular compiler tax. An example of something that inline assembly would handle badly would be broadcast, which x86 pre-AVX-512 only can do with a value already in a SIMD register, or directly from memory, but the programmer almost always will want to provide it as a regular scalar variable, i.e. GPR.