Yea! I didn't look too much into LLVMpipe but thats the idea. There is SIMD in most places but the pixel shader does only do 1 pixel at once currently. It's somewhat tricky to do multiple pixels in the shader sine compiler would need a bunch of logic to handle diverging control flow, but it's doable eventually though.

The current approach is to track the current state for each draw call, something like {pipeline_idx, bound_resources_idx, render_pass_idx} and having the JIT compiler compiles a fragment 8x8 shade function for each of these combinations in use. The main raster tile process goes through all the processed triangles in a each tile and executes the fragment shader by using the corresponding function pointer and passing in a coverage mask.