For some reasone that is not yet clear the piglit gl-1.0-rendermode-feedback makes use of the LLVM pipe draw module and fails there with an assertion. Explicietly disabling LLVM fixes this.
90a7d2e08fb r600: Make sure LLVM is not used for DRAW
src/gallium/drivers/r600/r600_pipe_common.c | 5 +++++
1 file changed, 5 insertions(+)