Alt+Tab on my kaveri 7650k system with 4k+full-hd screens (amdgpu, linux-4.15.9, mesa-17.3.6) running kde/kwin with compositor enabled results in:

Thread 26 "gallium_drv:0" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fff63fff700 (LWP 9101)]
si_draw_vbo (ctx=0x555556963dc0, info=0x5555569d7be8) at si_state_draw.c:1372
1372			} else if (sctx->b.chip_class <= CIK &&
#0  0x00007fffc37fa890 in si_draw_vbo (ctx=0x555556963dc0, info=0x5555569d7be8) at si_state_draw.c:1372
        sctx = 0x555556963dc0
        rs = <optimized out>
        indexbuf = 0x0
        dirty_tex_counter = <optimized out>
        rast_prim = <optimized out>
        index_size = 2
        index_offset = 0
#1  0x00007fffc351d593 in tc_call_draw_vbo (pipe=<optimized out>, payload=0x5555569d7be8) at util/u_threaded_context.c:1816
        info = 0x5555569d7be8
#2  0x00007fffc351a990 in tc_batch_execute (job=job@entry=0x5555569d7340, thread_index=thread_index@entry=0) at util/u_threaded_context.c:94
        iter = 0x5555569d7be0
        batch = 0x5555569d7340
        pipe = 0x555556963dc0
        last = 0x5555569d7fa0
#3  0x00007fffc33e2fda in util_queue_thread_func (input=input@entry=0x55555688f1c0) at u_queue.c:187
        job = {job = 0x5555569d7340, fence = 0x5555569d7350, execute = 0x7fffc351a950 <tc_batch_execute>, cleanup = 0x0}
        queue = 0x5555569d5978
        thread_index = 0
#4  0x00007fffc33e2e67 in impl_thrd_routine (p=<optimized out>) at ../../include/c11/threads_posix.h:87
        pack = {func = 0x7fffc33e2ea0 <util_queue_thread_func>, arg = 0x55555688f1c0}
#5  0x00007ffff02e050b in start_thread () at /lib64/libpthread.so.0
#6  0x00007fffecaa716f in clone () at /lib64/libc.so.6