imageStoreFast provides a variant of imageStore which does
not perform any bounds checking, reducing shader divergence,
register pressure and increasing performance through fewer
instructions.
However, this should only be used for cases where the writing
coordinate is guaranteed to fall within the texture.
Authored by Apple: Michael Parkin-White
Pull Request: https://projects.blender.org/blender/blender/pulls/111750
109bc2d416