Intel's improved GL Shading Language compiler has been living in Mesa master for nearly one year and is used by all Mesa / Gallium3D drivers, but it's still not yet perfect and still there are a variety of areas to improve. One of the features that's been missing in the Mesa GLSL compiler up to this point is support for use-define chains, but now that's finally coming.
Ian Romanick has published his Mesa ud-chains branch that provides this support to clear up some ugly hacks within Mesa's core code-base. For those interested in more technical details about this ud-chains work for Mesa's GLSL compiler, see Ian's blog post.
Right now the code is living in a separate branch, but hopefully it will end up being yet another feature for Mesa 7.11.