Unfortunately the page http://gpuopen.com/gcn-shader-extensions-for-direct3d-and-vulkan/ does not contain any information.
Also nothing here: https://www.opengl.org/registry/specs/ARB/shader_ballot.txt
Trying to compile with AMDs glslangValidator only gives me 'no matching overloaded function found', no matter how many parameters i give.
So, is the extension working and what are the function parameters we need to set? What's the returned value?