Created attachment 94348 [details]
dump

I noticed it suddently started working flawlessly so I asked myself what fixed
it: patches from https://bugs.freedesktop.org/show_bug.cgi?id=72785 did fix it.

I currently apply:
0001-SelectionDAG-Factor-ISD-MUL-lowering-code-out-of-DAG.patch
0002-SelectionDAG-Use-helper-function-to-improve-legaliza.patch
0001-R600-SI-Custom-select-64-bit-ADD.patch

Beware that I modified "UP.Threshold = 500" to "UP.Threshold = 100" because
"bfgminer --scrypt" didn't work otherwise.

I attached dump from R600_DEBUG=cs GEGL_USE_OPENCL=yes gimp without the
patches.