Allocating zero URB space is a really bad idea. The hardware has to
give threads a handle to their URB space, and threads have to use that
to terminate the thread. Having it be an empty region just breaks a
lot of assumptions. Hence, why we asserted that it isn't possible.
Unfortunately, it /is/ possible prior to Gen8, if max_vertices = 0.
In theory a geometry shader could do SSBO/image access and maybe
still accomplish something. In reality, this is tripped up by
conformance tests.
Gen8+ already avoids this problem by placing the vertex count DWord
in the URB entry header. This fixes things on earlier generations.
Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
Tested-by: Ian Romanick <ian.d.romanick@intel.com>
if (compiler->devinfo->gen >= 8)
output_size_bytes += 32;
- assert(output_size_bytes >= 1);
+ /* Shaders can technically set max_vertices = 0, at which point we
+ * may have a URB size of 0 bytes. Nothing good can come from that,
+ * so enforce a minimum size.
+ */
+ if (output_size_bytes == 0)
+ output_size_bytes = 1;
+
unsigned max_output_size_bytes = GEN7_MAX_GS_URB_ENTRY_SIZE_BYTES;
if (compiler->devinfo->gen == 6)
max_output_size_bytes = GEN6_MAX_GS_URB_ENTRY_SIZE_BYTES;