Handle "as" in kernel with ir.AsExpression case.

pkg/compiler/lib/src/ssa/builder_kernel.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:kernel/ast.dart' as ir;
 
 import '../common.dart';
 import '../common/codegen.dart' show CodegenRegistry, CodegenWorkItem;
 import '../common/names.dart';
 import '../common/tasks.dart' show CompilerTask;
@@ skipping 653 matching lines @@
 
   @override
   void visitIfStatement(ir.IfStatement ifStatement) {
     handleIf(
         visitCondition: () => ifStatement.condition.accept(this),
         visitThen: () => ifStatement.then.accept(this),
         visitElse: () => ifStatement.otherwise?.accept(this));
   }
 
   @override
+  void visitAsExpression(ir.AsExpression asExpression) {
+    asExpression.operand.accept(this);
+    HInstruction expressionInstruction = pop();
+    DartType type = astAdapter.getDartType(asExpression.type);
+    if (type.isMalformed) {
+      if (type is MalformedType) {
+        ErroneousElement element = type.element;
+        generateTypeError(asExpression, element.message);
+      } else {
+        assert(type is MethodTypeVariableType);
+        stack.add(expressionInstruction);
+      }
+    } else {
+      HInstruction converted = typeBuilder.buildTypeConversion(
+          expressionInstruction,
+          localsHandler.substInContext(type),
+          HTypeConversion.CAST_TYPE_CHECK);
+      if (converted != expressionInstruction) {
+        add(converted);
+      }
+      stack.add(converted);
+    }
+  }
+
+  void generateError(ir.Node node, String message, TypeMask typeMask) {
+    HInstruction errorMessage =
+        graph.addConstantString(new DartString.literal(message), compiler);
+    _pushStaticInvocation(node, [errorMessage], typeMask);
+  }
+
+  void generateTypeError(ir.Node node, String message) {
+    generateError(node, message, astAdapter.throwTypeErrorType);
+  }
+
+  @override
   void visitAssertStatement(ir.AssertStatement assertStatement) {
     if (!compiler.options.enableUserAssertions) return;
     if (assertStatement.message == null) {
       assertStatement.condition.accept(this);
       _pushStaticInvocation(astAdapter.assertHelper, <HInstruction>[pop()],
           astAdapter.assertHelperReturnType);
       pop();
       return;
     }
 
@@ skipping 903 matching lines @@
     push(new HNot(popBoolified(), backend.boolType));
   }
 
   @override
   void visitStringConcatenation(ir.StringConcatenation stringConcat) {
     KernelStringBuilder stringBuilder = new KernelStringBuilder(this);
     stringConcat.accept(stringBuilder);
     stack.add(stringBuilder.result);
   }
 }