[csa] Add Unreachable() and use it after throw sites

src/builtins/builtins-string.cc

 // Copyright 2016 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/builtins/builtins-regexp.h"
 #include "src/builtins/builtins-utils.h"
 #include "src/builtins/builtins.h"
 #include "src/code-factory.h"
 #include "src/code-stub-assembler.h"
 #include "src/regexp/regexp-utils.h"
@@ skipping 1888 matching lines @@
     StoreObjectFieldNoWriteBarrier(result, JSIteratorResult::kValueOffset,
                                    var_value.value());
     StoreObjectFieldNoWriteBarrier(result, JSIteratorResult::kDoneOffset,
                                    var_done.value());
     Return(result);
   }
 
   Bind(&throw_bad_receiver);
   {
     // The {receiver} is not a valid JSGeneratorObject.
-    Node* result =
-        CallRuntime(Runtime::kThrowIncompatibleMethodReceiver, context,
-                    HeapConstant(factory()->NewStringFromAsciiChecked(
-                        "String Iterator.prototype.next", TENURED)),
-                    iterator);
-    Return(result);  // Never reached.
+    CallRuntime(Runtime::kThrowIncompatibleMethodReceiver, context,
+                HeapConstant(factory()->NewStringFromAsciiChecked(
+                    "String Iterator.prototype.next", TENURED)),
+                iterator);
+    Unreachable();
   }
 }
 
 namespace {
 
 inline bool ToUpperOverflows(uc32 character) {
   // y with umlauts and the micro sign are the only characters that stop
   // fitting into one-byte when converting to uppercase.
   static const uc32 yuml_code = 0xff;
   static const uc32 micro_code = 0xb5;
@@ skipping 177 matching lines @@
 
 BUILTIN(StringPrototypeToUpperCase) {
   HandleScope scope(isolate);
   TO_THIS_STRING(string, "String.prototype.toUpperCase");
   return ConvertCase(string, isolate,
                      isolate->runtime_state()->to_upper_mapping());
 }
 
 }  // namespace internal
 }  // namespace v8