HLSL2GLSL does not look like it is part of the driver. It looks like it is a command line tool for converting someone's HLSL to the equivalent GLSL(in an attempt to promote pc game ports). So a developer of a game for Mac(using OpenGL) they do not have to rewrite their HLSL shaders. It looks like a convenience for developers. I could not find anything regarding the use of this conversion inside the graphics drivers. That wouldn't make much sense anyway, the compiled HLSL or GLSL should be compiled down to hardware specific tokens.