The GCN architecture contains a lot of functionality in the shader cores which is not currently exposed in current APIs like Vulkan™ or Direct3D® 12. One of the mandates of GPUOpen is to give developers better access to the hardware, and today we're releasing extensions for these APIs to expose additional GCN features to developers.
With those shader extensions, we provide access to wavefront-wide functions, which is an important building block to exploit the SIMD execution model of GPUs. For instance, the use of mbcnt and ballot can replace atomics in various cases, drastically boosting performance. The wavefront-wide instructions also include swizzles, which allow individual lanes to exchange data without going through memory.
Additionally, we expose readfirstlane and other functions which enable the compiler to move data from VGPRs into SGPRs. Especially for VGPR heavy code, marking variables as wavefront-uniform can reduce the VGPR count significantly.
Another often-requested feature which is getting exposed today is direct access to the barycentric coordinates. This is again an important building block for various algorithms.
Finally, we also provide various utility functions. In this release, we're providing the 3-parameter min, max and med functions which map directly to the corresponding GCN opcodes
Read more... (http://gpuopen.com/gcn-shader-extensions-for-direct3d-and-vulkan/)