Running my OpenCL app on Intel GPUs I encountered precision issue. Results were too imprecise and often failed to pass validation vs CPU-based (or AMD/nVidia GPU based) ones.
Considerable improvement was only when I refused from native_cos/native_sin in oclFFT (Apple's FFT release for OpenCL) and in other parts of app code.
I have no such issues with same OpenCL code on GPUs from other vendors (both AMD and nVidia).
Please consider some improvements for native trigonometric function presion in future SDK/hardware releases. Too low precision makes them just un-useful no matter how speedy they are. Make precision at least in line with other vendors.