[turbofan] Add new StringFromCharCode simplified operator.

test/unittests/compiler/js-builtin-reducer-unittest.cc

Index: test/unittests/compiler/js-builtin-reducer-unittest.cc
diff --git a/test/unittests/compiler/js-builtin-reducer-unittest.cc b/test/unittests/compiler/js-builtin-reducer-unittest.cc
index 0f8eed7958587baf4ff6445d1f2fc0caa9557261..c0af1d040f59baddab6414b68b0a9fb2fcffb5f6 100644
--- a/test/unittests/compiler/js-builtin-reducer-unittest.cc
+++ b/test/unittests/compiler/js-builtin-reducer-unittest.cc
@@ -49,6 +49,19 @@ class JSBuiltinReducerTest : public TypedGraphTest {
     return HeapConstant(f);
   }
 
+  Node* StringFunction(const char* name) {
+    Handle<Object> m =
+        JSObject::GetProperty(
+            isolate()->global_object(),
+            isolate()->factory()->NewStringFromAsciiChecked("String"))
+            .ToHandleChecked();
+    Handle<JSFunction> f = Handle<JSFunction>::cast(
+        Object::GetProperty(
+            m, isolate()->factory()->NewStringFromAsciiChecked(name))
+            .ToHandleChecked());
+    return HeapConstant(f);
+  }
+
   JSOperatorBuilder* javascript() { return &javascript_; }
 
  private:
@@ -189,6 +202,28 @@ TEST_F(JSBuiltinReducerTest, MathFround) {
   }
 }
 
+// -----------------------------------------------------------------------------
+// String.fromCharCode
+
+TEST_F(JSBuiltinReducerTest, StringFromCharCode) {
+  Node* function = StringFunction("fromCharCode");
+
+  Node* effect = graph()->start();
+  Node* control = graph()->start();
+  Node* context = UndefinedConstant();
+  Node* frame_state = graph()->start();
+  TRACED_FOREACH(Type*, t0, kNumberTypes) {
+    Node* p0 = Parameter(t0, 0);
+    Node* call = graph()->NewNode(javascript()->CallFunction(3), function,
+                                  UndefinedConstant(), p0, context, frame_state,
+                                  frame_state, effect, control);
+    Reduction r = Reduce(call);
+
+    ASSERT_TRUE(r.Changed());
+    EXPECT_THAT(r.replacement(), IsStringFromCharCode(p0));
+  }
+}
+
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8