Return infinite layout size for SpecializationConstants

Author: aidanfnv

source/slang/slang-type-layout.cpp

@@ -2475,6 +2475,32 @@ static LayoutSize GetElementCount(IntVal* val)
     }
     else if (const auto varRefVal = as<DeclRefIntVal>(val))
     {
+        // Check if this is a specialization constant
+        if (auto declRef = varRefVal->getDeclRef())
+        {
+            auto varDecl = declRef.as<VarDeclBase>();
+            if (varDecl && (varDecl.getDecl()->hasModifier<SpecializationConstantAttribute>() ||
+                            varDecl.getDecl()->hasModifier<VkConstantIdAttribute>()))
+            {
+                // Specialization constants can be overridden at pipeline-creation time
+                // (e.g., in vkCreateComputePipelines), so we cannot rely on their default values
+                // during layout calculation. The actual runtime value may differ from the default,
+                // and the default itself could even be zero.
+                //
+                // We treat specialization-constant-sized arrays as "unbounded" (infinite) for
+                // layout purposes to ensure descriptor bindings are allocated regardless of the
+                // default value:
+                // - If default is 0 but runtime is 128, we still need the binding
+                // - The containing type must be recognized as having uniform data
+                // - Descriptor set/binding allocation is independent of array size
+                // - Array sizes are expressed symbolically (via OpSpecConstantOp) during SPIR-V
+                //   emission, then evaluated to concrete bytes at pipeline-creation time
+                //
+                // This differs from generic parameters, which are resolved at Slang compile-time
+                return LayoutSize::infinite();
+            }
+        }
+
         // TODO: We want to treat the case where the number of
         // elements in an array depends on a generic parameter
         // much like the case where the number of elements is