[dyn_modules,dart2bytecode] Fix isTop predicate for extension types in bytecode generator

Bytecode generator needs to know the runtime semantics of Dart types,
but TypeEnvironment.isTop predicate does not use erasure of extension
types and does not return true for extension types based on other top
types (e.g. dynamic).

TEST=language/dot_shorthands/member/static_method_cascade_test

Change-Id: If8323d11293498fb39d8d936c406bc9bb7e85ce9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/426983
Commit-Queue: Alexander Markov <[email protected]>
Reviewed-by: Slava Egorov <[email protected]>

Author: alexmarkov

pkg/dart2bytecode/lib/bytecode_generator.dart

@@ -1503,7 +1503,7 @@ class BytecodeGenerator extends RecursiveVisitor {
 
   /// Generates is-test for the value at TOS.
   void _genInstanceOf(DartType type) {
-    if (typeEnvironment.isTop(type)) {
+    if (_isTopType(type)) {
       asm.emitDrop1();
       asm.emitPushTrue();
       return;
@@ -2227,7 +2227,7 @@ class BytecodeGenerator extends RecursiveVisitor {
     final DartType bound = (forwardingTypeParameterBounds != null)
         ? forwardingTypeParameterBounds[typeParam]!
         : typeParam.bound;
-    if (typeEnvironment.isTop(bound)) {
+    if (_isTopType(bound)) {
       return false;
     }
     return true;
@@ -2244,7 +2244,7 @@ class BytecodeGenerator extends RecursiveVisitor {
     final DartType type = (forwardingParameterTypes != null)
         ? forwardingParameterTypes[param]!
         : param.type;
-    if (typeEnvironment.isTop(type)) {
+    if (_isTopType(type)) {
       return false;
     }
     return true;
@@ -2289,6 +2289,16 @@ class BytecodeGenerator extends RecursiveVisitor {
     asm.emitAssertSubtype();
   }
 
+  bool _isTopType(DartType type) => switch (type) {
+        DynamicType() => true,
+        VoidType() => true,
+        InterfaceType() => type.classNode == coreTypes.objectClass &&
+            type.nullability == Nullability.nullable,
+        FutureOrType() => _isTopType(type.typeArgument),
+        ExtensionType() => _isTopType(type.extensionTypeErasure),
+        _ => false,
+      };
+
   void _genArgumentTypeCheck(VariableDeclaration variable,
       Map<VariableDeclaration, DartType>? forwardingParameterTypes) {
     final DartType type = (forwardingParameterTypes != null)
@@ -2300,7 +2310,7 @@ class BytecodeGenerator extends RecursiveVisitor {
   }
 
   void _genAssertAssignable(DartType type, {String? name, String? message}) {
-    assert(!typeEnvironment.isTop(type));
+    assert(!_isTopType(type));
     asm.emitPushConstant(cp.addType(type));
     _genPushInstantiatorAndFunctionTypeArguments([type]);
     asm.emitPushConstant(
@@ -2723,7 +2733,7 @@ class BytecodeGenerator extends RecursiveVisitor {
     _generateNode(node.operand);
 
     final type = node.type;
-    if (typeEnvironment.isTop(type)) {
+    if (_isTopType(type) || node.isUnchecked) {
       return;
     }