[Interpreter] Ensure that implicit return undefined is generated.

test/cctest/interpreter/test-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/v8.h"
 
 #include "src/compiler.h"
 #include "src/interpreter/bytecode-generator.h"
 #include "src/interpreter/interpreter.h"
 #include "test/cctest/cctest.h"
@@ skipping 61 matching lines @@
 #define B(x) static_cast<uint8_t>(Bytecode::k##x)
 #define U8(x) static_cast<uint8_t>((x) & 0xff)
 #define R(x) static_cast<uint8_t>(-(x) & 0xff)
 
 
 TEST(PrimitiveReturnStatements) {
   InitializedHandleScope handle_scope;
   BytecodeGeneratorHelper helper;
 
   ExpectedSnippet<void*> snippets[] = {
+      {"", 0, 1, 2, {B(LdaUndefined), B(Return)}, 0},
       {"return;", 0, 1, 2, {B(LdaUndefined), B(Return)}, 0},
       {"return null;", 0, 1, 2, {B(LdaNull), B(Return)}, 0},
       {"return true;", 0, 1, 2, {B(LdaTrue), B(Return)}, 0},
       {"return false;", 0, 1, 2, {B(LdaFalse), B(Return)}, 0},
       {"return 0;", 0, 1, 2, {B(LdaZero), B(Return)}, 0},
       {"return +1;", 0, 1, 3, {B(LdaSmi8), U8(1), B(Return)}, 0},
       {"return -1;", 0, 1, 3, {B(LdaSmi8), U8(-1), B(Return)}, 0},
       {"return +127;", 0, 1, 3, {B(LdaSmi8), U8(127), B(Return)}, 0},
       {"return -128;", 0, 1, 3, {B(LdaSmi8), U8(-128), B(Return)}, 0},
   };
@@ skipping 322 matching lines @@
       Handle<String> expected = helper.factory()->NewStringFromAsciiChecked(
           snippets[i].constants[j]);
       CHECK(String::cast(ba->constant_pool()->get(j))->Equals(*expected));
     }
   }
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespance v8