iris: non-coherent framebuffer fetch broken with layered rendering and non-zero base layer on a 3D framebuffer on BDW
If you are trying to do non-coherent framebuffer fetch (or blend_equation_advanced) on a 3D framebuffer with layered rendering and a non-zero base layer, iris does the wrong thin. We texture from the 3D texture as requested but the HW ignores the base layer so we get the wrong data.
The only real fix for this is to push a base layer into the shader as a uniform.
See also !11235 (comment 950834)