Same here on TAHITI (Radeon HD 7950) with Mesa git e93566a, LLVM svn r228889
and kernel 3.18.6-gentoo.

I can confirm that reverting 0e9cdedd2e3943bdb7f3543a3508b883b167e427 fixes the
grass, but it also brings back the GPU fault errors in dmesg from bug #87278,
although not reproducible with the first apitrace there. Here's a new apitrace
showing both the missing grass (with 0e9cded) or GPU faults (with 0e9cded
reverted):

 http://constexpr.org/tmp/TalosDemo-radeonsi.2.trace.xz (83 MiB)