[JS IR] Improve performance for runtime typecheck

This is a part of KT-42743

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/JsClassGenerator.kt

@@ -31,7 +31,7 @@ class JsClassGenerator(private val irClass: IrClass, val context: JsGenerationCo
     private val baseClass: IrType? = irClass.superTypes.firstOrNull { !it.classifierOrFail.isInterface }
 
     private val baseClassRef by lazy { // Lazy in case was not collected by namer during JsClassGenerator construction
-        baseClass?.getClassRef(context)
+        if (baseClass != null && !baseClass.isAny()) baseClass.getClassRef(context) else null
     }
     private val classPrototypeRef = prototypeOf(classNameRef)
     private val classBlock = JsGlobalBlock()
@@ -49,11 +49,7 @@ class JsClassGenerator(private val irClass: IrClass, val context: JsGenerationCo
         // We'll use IrSimpleFunction::correspondingProperty to collect them into set
         val properties = mutableSetOf<IrProperty>()
 
-        val jsClass = JsClass(name = className)
-
-        if (baseClass != null && !baseClass.isAny()) {
-            jsClass.baseClass = baseClassRef
-        }
+        val jsClass = JsClass(name = className, baseClass = baseClassRef)
 
         if (es6mode) classModel.preDeclarationBlock.statements += jsClass.makeStmt()
 
@@ -329,12 +325,10 @@ class JsClassGenerator(private val irClass: IrClass, val context: JsGenerationCo
     }
 
     private fun generateInheritanceCode(): List<JsStatement> {
-        if (baseClass == null || baseClass.isAny()) {
-            return emptyList()
-        }
+        val baseClassPrototype = baseClassRef ?: return emptyList()
 
         val createCall = jsAssignment(
-            classPrototypeRef, JsInvocation(Namer.JS_OBJECT_CREATE_FUNCTION, prototypeOf(baseClassRef!!))
+            classPrototypeRef, JsInvocation(Namer.JS_OBJECT_CREATE_FUNCTION, prototypeOf(baseClassPrototype))
         ).makeStmt()
 
         val ctorAssign = jsAssignment(JsNameRef(Namer.CONSTRUCTOR_NAME, classPrototypeRef), classNameRef).makeStmt()
@@ -364,6 +358,8 @@ class JsClassGenerator(private val irClass: IrClass, val context: JsGenerationCo
 
         metadataLiteral.propertyInitializers += generateAssociatedKeyProperties()
 
+        generateFastPrototype()?.let { metadataLiteral.propertyInitializers += it }
+
         if (isCoroutineClass()) {
             metadataLiteral.propertyInitializers += generateSuspendArity()
         }
@@ -403,6 +399,10 @@ class JsClassGenerator(private val irClass: IrClass, val context: JsGenerationCo
         )
     }
 
+    private fun generateFastPrototype() = baseClassRef?.let {
+        JsPropertyInitializer(JsNameRef(Namer.METADATA_FAST_PROTOTYPE), prototypeOf(it))
+    }
+
     private fun IrType.isFunctionType() = isFunctionOrKFunction() || isSuspendFunctionOrKFunction()
 
     private fun generateAssociatedKeyProperties(): List<JsPropertyInitializer> {

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/utils/Namer.kt

@@ -34,6 +34,7 @@ object Namer {
     val METADATA_INTERFACES = "interfaces"
     val METADATA_SIMPLE_NAME = "simpleName"
     val METADATA_CLASS_KIND = "kind"
+    val METADATA_FAST_PROTOTYPE = "fastPrototype"
     val METADATA_SUSPEND_ARITY = "suspendArity"
 
     val KCALLABLE_GET_NAME = "<get-name>"