anv: Allow unused VkSpecializationMapEntries

Fixes future CTS: dEQP-VK.pipeline.spec_constant.*.basic.*unused_*

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11987>

src/intel/vulkan/anv_pipeline.c

@@ -117,8 +117,27 @@ anv_shader_compile_to_nir(struct anv_device *device,
          case 1:
             spec_entries[i].value.u8 = *(const uint8_t *)data;
             break;
+         case 0:
          default:
-            assert(!"Invalid spec constant size");
+            /* The Vulkan spec says:
+             *
+             *    "For a constantID specialization constant declared in a
+             *    shader, size must match the byte size of the constantID. If
+             *    the specialization constant is of type boolean, size must be
+             *    the byte size of VkBool32."
+             *
+             * Therefore, since only scalars can be decorated as
+             * specialization constants, we can assume that if it doesn't have
+             * a size of 1, 2, 4, or 8, any use in a shader would be invalid
+             * usage.  The spec further says:
+             *
+             *    "If a constantID value is not a specialization constant ID
+             *    used in the shader, that map entry does not affect the
+             *    behavior of the pipeline."
+             *
+             * so we should ignore any invalid specialization constants rather
+             * than crash or error out when we see one.
+             */
             break;
          }
       }