[turbofan] Add new StringFromCharCode simplified operator.

src/compiler/simplified-lowering.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/simplified-lowering.h"
 
 #include <limits>
 
 #include "src/address-map.h"
 #include "src/base/bits.h"
@@ skipping 1152 matching lines @@
               flags, properties);
           node->InsertInput(jsgraph_->zone(), 0,
                             jsgraph_->HeapConstant(callable.code()));
           node->AppendInput(jsgraph_->zone(), jsgraph_->NoContextConstant());
           node->AppendInput(jsgraph_->zone(), jsgraph_->graph()->start());
           node->AppendInput(jsgraph_->zone(), jsgraph_->graph()->start());
           NodeProperties::ChangeOp(node, jsgraph_->common()->Call(desc));
         }
         break;
       }
+      case IrOpcode::kStringFromCharCode: {
+        VisitUnop(node, UseInfo::TruncatingWord32(),
+                  MachineRepresentation::kTagged);
+        break;
+      }
       case IrOpcode::kStringToNumber: {
         VisitUnop(node, UseInfo::AnyTagged(), MachineRepresentation::kTagged);
         if (lower()) {
           // StringToNumber(x) => Call(StringToNumberStub, x, no-context)
           Operator::Properties properties = Operator::kNoThrow;
           Callable callable = CodeFactory::StringToNumber(jsgraph_->isolate());
           CallDescriptor::Flags flags = CallDescriptor::kNoFlags;
           CallDescriptor* desc = Linkage::GetStubCallDescriptor(
               jsgraph_->isolate(), jsgraph_->zone(), callable.descriptor(), 0,
               flags, properties);
@@ skipping 1283 matching lines @@
         isolate(), graph()->zone(), callable.descriptor(), 0, flags,
         Operator::kNoProperties);
     to_number_operator_.set(common()->Call(desc));
   }
   return to_number_operator_.get();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8