[turbofan] Add new StringFromCharCode simplified operator.

src/compiler/js-builtin-reducer.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/js-builtin-reducer.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 #include "src/compiler/simplified-operator.h"
 #include "src/objects-inl.h"
@@ skipping 198 matching lines @@
 Reduction JSBuiltinReducer::ReduceMathTrunc(Node* node) {
   JSCallReduction r(node);
   if (r.InputsMatchOne(Type::Number())) {
     // Math.trunc(a:number) -> NumberTrunc(a)
     Node* value = graph()->NewNode(simplified()->NumberTrunc(), r.left());
     return Replace(value);
   }
   return NoChange();
 }
 
+// ES6 section 21.1.2.1 String.fromCharCode ( ...codeUnits )
+Reduction JSBuiltinReducer::ReduceStringFromCharCode(Node* node) {
+  JSCallReduction r(node);
+  if (r.InputsMatchOne(Type::Number())) {
+    // String.fromCharCode(a:number) -> StringFromCharCode(a)
+    Node* value =
+        graph()->NewNode(simplified()->StringFromCharCode(), r.left());
+    return Replace(value);
+  }
+  return NoChange();
+}
+
 Reduction JSBuiltinReducer::Reduce(Node* node) {
   Reduction reduction = NoChange();
   JSCallReduction r(node);
 
   // Dispatch according to the BuiltinFunctionId if present.
   if (!r.HasBuiltinFunctionId()) return NoChange();
   switch (r.GetBuiltinFunctionId()) {
     case kMathMax:
       reduction = ReduceMathMax(node);
       break;
@@ skipping 14 matching lines @@
       break;
     case kMathRound:
       reduction = ReduceMathRound(node);
       break;
     case kMathSqrt:
       reduction = ReduceMathSqrt(node);
       break;
     case kMathTrunc:
       reduction = ReduceMathTrunc(node);
       break;
+    case kStringFromCharCode:
+      reduction = ReduceStringFromCharCode(node);
+      break;
     default:
       break;
   }
 
   // Replace builtin call assuming replacement nodes are pure values that don't
   // produce an effect. Replaces {node} with {reduction} and relaxes effects.
   if (reduction.Changed()) ReplaceWithValue(node, reduction.replacement());
 
   return reduction;
 }
@@ skipping 15 matching lines @@
 }
 
 
 SimplifiedOperatorBuilder* JSBuiltinReducer::simplified() const {
   return jsgraph()->simplified();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8