That's actually generally not true WRT SIMD/vector instructions (see eg http://yosefk.com/blog/humans-and-compilers-need-each-other-the-vliw-simd-case.html http

That's actually generally not true WRT SIMD/vector instructions (see eg http://yosefk.com/blog/humans-and-compilers-need-each-other-the-vliw-simd-case.html http://yosefk.com/blog/humans-and-compilers-need-each-other-... which contrasts this with the more compiler-friendly VLIW case); they impose nontrivial requirements on data structures and ABI, so the application code needs to at least be aware of the possibility of vectorization, even if it's agnostic to whether the implementation actually uses it.