The compiler for sure does some vectorization for me currently, I would expect much worse performance otherwise, it's quite good at that

The SIMD idea there was more in the direction of structuring the data in a more vector friendly way, and then seeing if manually vectorized code would run better - but right now I haven't really invested much time into it :/

There's also multi threading which I wanted to add, by having the rasterizer handle triangles in parallel in different regions of the screen, but this is also just an idea which I haven't explored much yet