[turbofan] Add new StringFromCharCode simplified operator.

src/compiler/typer.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/typer.h"
 
 #include "src/base/flags.h"
 #include "src/bootstrapper.h"
 #include "src/compilation-dependencies.h"
 #include "src/compiler/common-operator.h"
@@ skipping 254 matching lines @@
 
 #define DECLARE_METHOD(x) static Type* x##Typer(Type*, Type*, Typer*);
   JS_SIMPLE_BINOP_LIST(DECLARE_METHOD)
 #undef DECLARE_METHOD
 
   static Type* JSTypeOfTyper(Type*, Typer*);
   static Type* JSLoadPropertyTyper(Type*, Type*, Typer*);
   static Type* JSCallFunctionTyper(Type*, Typer*);
 
   static Type* ReferenceEqualTyper(Type*, Type*, Typer*);
+  static Type* StringFromCharCodeTyper(Type*, Typer*);
 
   Reduction UpdateType(Node* node, Type* current) {
     if (NodeProperties::IsTyped(node)) {
       // Widen the type of a previously typed node.
       Type* previous = NodeProperties::GetType(node);
       if (node->opcode() == IrOpcode::kPhi) {
         // Speed up termination in the presence of range types:
         current = Weaken(node, current, previous);
       }
 
@@ skipping 1522 matching lines @@
 }
 
 Type* Typer::Visitor::TypeStringEqual(Node* node) { return Type::Boolean(); }
 
 Type* Typer::Visitor::TypeStringLessThan(Node* node) { return Type::Boolean(); }
 
 Type* Typer::Visitor::TypeStringLessThanOrEqual(Node* node) {
   return Type::Boolean();
 }
 
+Type* Typer::Visitor::StringFromCharCodeTyper(Type* type, Typer* t) {
+  type = NumberToUint32(ToNumber(type, t), t);
+  Factory* f = t->isolate()->factory();
+  double min = type->Min();
+  double max = type->Max();
+  if (min == max) {
+    uint32_t code = static_cast<uint32_t>(min) & String::kMaxUtf16CodeUnitU;
+    Handle<String> string = f->LookupSingleCharacterStringFromCode(code);
+    return Type::Constant(string, t->zone());
+  }
+  return Type::String();
+}
+
+Type* Typer::Visitor::TypeStringFromCharCode(Node* node) {
+  return TypeUnaryOp(node, StringFromCharCodeTyper);
+}
+
 Type* Typer::Visitor::TypeStringToNumber(Node* node) {
   return TypeUnaryOp(node, ToNumber);
 }
 
 namespace {
 
 Type* ChangeRepresentation(Type* type, Type* rep, Zone* zone) {
   return Type::Union(Type::Semantic(type, zone),
                      Type::Representation(rep, zone), zone);
 }
@@ skipping 771 matching lines @@
   }
   if (Type::IsInteger(*value)) {
     return Type::Range(value->Number(), value->Number(), zone());
   }
   return Type::Constant(value, zone());
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8