Win7 64 bit, 16 GB RAM, an AMD 7xxx GPU, third gen i7 processor
Broken: hash 8dea065
Worked: hash a3530b3
Short description of error
The absolute newest Win64 build available on the buildbot crashes whenever a scene has a material containing either a glass, refraction, and/or a glossy node.
Exact steps for others to reproduce the error
Select Cycles as render engine, change the shader of the default cube from diffuse to glossy, Blender will quit if you press F12 or you have the material preview open (whichever comes first). It won't matter if the distribution type is Beckmann or GGX..
I believe this issue is caused by the commit that added the 'sharp' closure fallback committed today.