[Interpreter] Ensure that implicit return undefined is generated.

src/interpreter/bytecode-generator.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/interpreter/bytecode-generator.h"
 
 #include <stack>
 
 #include "src/compiler.h"
 #include "src/objects.h"
@@ skipping 27 matching lines @@
   if (scope()->is_function_scope() && scope()->function() != NULL) {
     VisitVariableDeclaration(scope()->function());
   }
 
   // Visit declarations within the function scope.
   VisitDeclarations(scope()->declarations());
 
   // Visit statements in the function body.
   VisitStatements(info->literal()->body());
 
+  // If the last bytecode wasn't a return, then return 'undefined' to avoid
+  // falling off the end.
+  if (!builder_.HasExplicitReturn()) {
+    builder_.LoadUndefined();
+    builder_.Return();
+  }
+
   set_scope(nullptr);
   set_info(nullptr);
   return builder_.ToBytecodeArray();
 }
 
 
 void BytecodeGenerator::VisitBlock(Block* node) {
   if (node->scope() == NULL) {
     // Visit statements in the same scope, no declarations.
     VisitStatements(node->statements());
@@ skipping 350 matching lines @@
 }
 
 
 int BytecodeGenerator::feedback_index(FeedbackVectorICSlot slot) const {
   return info()->feedback_vector()->GetIndex(slot);
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8