freedreno/a6xx: debug build assert
seeing this in gfxbench on android (but oddly I haven't seen that on the linux version)
05-14 10:58:04.802 1169 2410 F libc : ../../master/src/gallium/drivers/freedreno/a6xx/fd6_vsc.c:117: unsigned int draw_stream_size_bits(const struct pipe_draw_info *, unsigned int, unsigned int): assertion "info->instance_count > 0" failed