R9285 since llvm commit 

commit 817178adc78bbd36ba635d3147cca53070558def
Author: Matthias Braun <matze@braunis.de>
Date:   Sat Mar 5 04:36:10 2016 +0000

    RegisterCoalescer: Need to check DstReg+SrcReg for missing undef flags

    copy coalescing with enabled subregister liveness can reveal undef uses,
    previously this was only checked for the SrcReg in updateRegDefsUses()
    but we need to check DstReg as well.

    git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262767
91177308-0d34-0410-b5e6-96231b3b80d8

Unigine Valley will assert at start of rendering.

valley_x64: /mnt/sdb1/Gits/llvm/lib/CodeGen/MachineScheduler.cpp:1046: void
llvm::ScheduleDAGMILive::updatePressureDiffs(llvm::ArrayRef<llvm::RegisterMaskPair>):
Assertion `VNI && "No live value at use."' failed.


Other demos don't trigger this.

Valley is running 1920x1080 fullscreen ultra quality + 8x AA.