[PATCH vkd3d v2 3/3] vkd3d-shader: Emit SPIR-V for descriptor arrays and arrayed bindings.

[Henri Verbeet]

On Tue, 15 Jun 2021 at 14:55, Conor McCarthy <cmccarthy at codeweavers.com> wrote:
> June 15, 2021 8:36 PM, "Henri Verbeet" <hverbeet at gmail.com> wrote:
> > That's one possibility, but it would also be possible to just compare
> > the "count" field from the vkd3d_shader_descriptor_binding structure
> > against 1, instead of comparing "binding_base_idx" against ~0u. (I.e.,
> > when storing a vkd3d_shader_descriptor_binding structure in the
> > vkd3d_array_variable/vkd3d_symbol_descriptor_binding structure.)
>
> The one potential problem I see is it's possible to declare in a shader an unbounded resource array which maps to a range containing only one descriptor, and then dynamically index it with a variable that's always zero. Unlikely to occur, but the dynamic indexing would fail because with binding.count == 1, a scalar variable is declared.

That's a good point, although also somewhat orthogonal; in the current
version of the patch vkd3d_dxbc_compiler_get_resource_variable() uses
the "array_variable" parameter to decide whether to create a scalar or
array variable. Its callers all use some variant of "binding_base_idx
!= ~0u || register_last == ~0u" to set that, which could be trivially
replaced with something like "binding.count > 1 || register_last ==
~0u", because vkd3d_dxbc_compiler_get_resource_variable() also takes
"binding" as an argument.

It could be argued that callers should pass a
vkd3d_shader_descriptor_range structure to
vkd3d_dxbc_compiler_get_resource_variable() instead of the
"array_variable" parameter, in which case
vkd3d_dxbc_compiler_get_resource_variable() would be able to resolve
whether or not to create an array variable for itself, using something
like "binding->count > 1 || range->last == ~0u". There's certainly
something to be said for the simplicity of always creating array
variables though.