Every once in a while, I hear how intrinsics have improved enough that it’s safe to use them for high performance code. That would be nice. The promise of intrinsics is that you can write optimized code by calling out to functions (intrinsics) that correspond to particular assembly instructions. Since intrinsics act like normal functions, they can be cross platform. And since your compiler has access to more computational power than your brain, as well as a detailed model of every CPU, the compiler should be able to do a better job of micro-optimizations. Despite decade old claims that intrinsics can make your life easier, it never seems to work out.
The last time I tried intrinsics was around 2007; for more on why they were hopeless then see this exploration by the author of VirtualDub. I gave them another shot recently, and while they’ve improved, they’re still not worth the effort. The problem is that intrinsics are so unreliable that you have to manually check the result on every platform and every compiler you expect your code to be run on, and then tweak the intrinsics until you get a reasonable result. That’s more work than just writing the assembly by hand. If you don’t check the results by hand, it’s easy to get bad results.