softgpu: Use SSE for gouraud shading.
softgpu: Use SSE for through texture coords.
softgpu: Use SSE for texture sampling.
softgpu: Don't multithread small triangles.

It ends up being slower with all the overhead, of course.
softgpu: Use a full Vec4 for the prim color.

Simpler, and slightly faster.
softgpu: Minor simplification for alpha blend.
softgpu: Optimize alpha blending handling.

This alone makes it a good bit faster.
softgpu: Get all tex samples at the same time.

Kills a bunch of overhead, improving speed more.
softgpu: Use SSE for the secondary color.

It's easy to speed up this code since it's so hot.
softgpu: Use SSE in Vec?::Length().

Minor perf boost but if I do everything in Vec things get slower.
softgpu: Use SSE in tex modulation.

Could do others, this seems the most common.  Gives a few more percent.
softgpu: Use SSE in alpha blending.
softgpu: Use SSE in ToRGB()/FromRGB() etc.
Oops, forgot to multiply in float ToRGBA().

Not actually used...
softgpu: Don't re-pack 8888 colors.

It's like a bad joke, but MSVC was not optimizing this out.
Merge pull request #5670 from unknownbrackets/softgpu

Use SSE in the softgpu to improve perf