Hi,

I've got what looks like a regression moving from 19.0.6 -> 19.1.0 running the intel vulkan driver on IvyBridge.  It seems that calling vkAllocateDescriptorSets with a COMBINED_IMAGE_SAMPLER that uses an immutable sampler causes a segfault.

I can reproduce this as an assert using a debug build from git today (8ea7ee153649ac07c8418cc0d4aa5a4e123d19d1), here is the top of the callstack:

#0  0x00007ffff7bd9755 in raise () from /usr/lib/libc.so.6
#1  0x00007ffff7bc4851 in abort () from /usr/lib/libc.so.6
#2  0x00007ffff7bc4727 in __assert_fail_base.cold () from /usr/lib/libc.so.6
#3  0x00007ffff7bd2026 in __assert_fail () from /usr/lib/libc.so.6
#4  0x00007ffff72f233a in anv_descriptor_set_write_image_view (device=0x5555561e9880, set=0x55555621a668, 
    info=0x7fffffff8740, type=VK_DESCRIPTOR_TYPE_SAMPLER, binding=0, element=0)
    at ../src/intel/vulkan/anv_descriptor_set.c:1203
#5  0x00007ffff72f16f9 in anv_descriptor_set_create (device=0x5555561e9880, pool=0x55555621a5d0, 
    layout=0x5555561220a0, out_set=0x7fffffff87c8) at ../src/intel/vulkan/anv_descriptor_set.c:971
#6  0x00007ffff72f19c8 in anv_AllocateDescriptorSets (_device=0x5555561e9880, pAllocateInfo=0x7fffffff9a58, 
    pDescriptorSets=0x7fffffff8900) at ../src/intel/vulkan/anv_descriptor_set.c:1030

It seems that anv_descriptor_set_create() calls anv_descriptor_set_write_image_view() to set up some stuff from the immutable sampler, but due to recent changes anv_descriptor_set_write_image_view() assumes that a layout that has the ANV_DESCRIPTOR_TEXTURE_SWIZZLE bit set always has a non-null image_view (which we do not since we are only creating the descriptor set at this stage).

If I patch the ANV_DESCRIPTOR_TEXTURE_SWIZZLE block at the end of anv_descriptor_set_write_image_view() to only update the swizzle descriptors if there is a non-null image_view, then my app goes back to running as expected.  I do not know if this is the correct fix for this issue though!