[turbofan] Add new StringFromCharCode simplified operator.

src/compiler/verifier.cc

 // Copyright 2014 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/compiler/verifier.h"
 
 #include <algorithm>
 #include <deque>
 #include <queue>
 #include <sstream>
@@ skipping 743 matching lines @@
       CheckUpperIs(node, Type::Boolean());
       break;
     case IrOpcode::kStringEqual:
     case IrOpcode::kStringLessThan:
     case IrOpcode::kStringLessThanOrEqual:
       // (String, String) -> Boolean
       CheckValueInputIs(node, 0, Type::String());
       CheckValueInputIs(node, 1, Type::String());
       CheckUpperIs(node, Type::Boolean());
       break;
+    case IrOpcode::kStringFromCharCode:
+      // Number -> String
+      CheckValueInputIs(node, 0, Type::Number());
+      CheckUpperIs(node, Type::String());
+      break;
     case IrOpcode::kStringToNumber:
       // String -> Number
       CheckValueInputIs(node, 0, Type::String());
       CheckUpperIs(node, Type::Number());
       break;
     case IrOpcode::kReferenceEqual: {
       // (Unique, Any) -> Boolean  and
       // (Any, Unique) -> Boolean
       CheckUpperIs(node, Type::Boolean());
       break;
@@ skipping 619 matching lines @@
          replacement->op()->EffectOutputCount() > 0);
   DCHECK(!NodeProperties::IsFrameStateEdge(edge) ||
          replacement->opcode() == IrOpcode::kFrameState);
 }
 
 #endif  // DEBUG
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8