On Mon, Dec 5, 2016 at 1:39 PM, Kenneth Graunke <kenn...@whitecape.org> wrote: > 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. > > Signed-off-by: Kenneth Graunke <kenn...@whitecape.org> > --- > src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp > b/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp > index 900d9d3..3894a63 100644 > --- a/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp > +++ b/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp > @@ -781,7 +781,13 @@ brw_compile_gs(const struct brw_compiler *compiler, void > *log_data, > 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; > -- > 2.10.2 > > _______________________________________________ > mesa-dev mailing list > mesa-dev@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/mesa-dev
Sounds reasonable to me. Reviewed-by: Anuj Phogat <anuj.pho...@gmail.com> _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev