GLAMOR acceleration is required for Radeon HD 7000 series and newer hardware acceleration while it's an optional alternative to EXA with the HD 6000 series and older. AMD's X.Org driver up to this point has relied upon the external GLAMOR library for accelerating 2D operations over OpenGL, but now it can use the in-server version of GLAMOR.
Developers at Intel landed GLAMOR into the X.Org Server at the beginning of the year for pushing more innovation and improvements to this universal means of 2D acceleration. This in-server GLAMOR has seen many significant improvements so far and we're still a few months out from seeing the official release of xorg-server 1.16.
While xf86-video-ati will continue to support the external GLAMOR library for the foreseeable future given modern AMD Radeon hardware needs GLAMOR but not everyone will quickly upgrade to X.Org Server 1.16+, the latest DDX Git code optionally supports the new in-server code.
Michel Dänzer added the support to xf86-video-ati Git this morning that supports building against GLAMOR within the X.Org Server tree if the code is available. The change happened with this Git commit. We will have our GLAMOR benchmarks in the coming weeks comparing the versions of GLAMOR once version 1.16 is closer to release.