Remove new space allocation in optimizing compiler, use Symbols::FromConcat where appropriate

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
diff --git a/runtime/vm/parser.cc b/runtime/vm/parser.cc
index af66c87f5b20376d8a63c353b0fd4b745791b392..c349982045aaaa2bf5869feaf126512557e1da73 100644
--- a/runtime/vm/parser.cc
+++ b/runtime/vm/parser.cc
@@ -1121,8 +1121,7 @@ ParsedFunction* Parser::ParseStaticFieldInitializer(const Field& field) {
 
   const String& field_name = String::Handle(zone, field.name());
   String& init_name = String::Handle(zone,
-      String::Concat(Symbols::InitPrefix(), field_name));
-  init_name = Symbols::New(init_name);
+      Symbols::FromConcat(Symbols::InitPrefix(), field_name));
 
   const Function& initializer = Function::ZoneHandle(zone,
       Function::New(init_name,
@@ -4840,8 +4839,7 @@ void Parser::ParseEnumDefinition(const Class& cls) {
 void Parser::AddImplicitConstructor(const Class& cls) {
   // The implicit constructor is unnamed, has no explicit parameter.
   String& ctor_name = String::ZoneHandle(Z, cls.Name());
-  ctor_name = String::Concat(ctor_name, Symbols::Dot());
-  ctor_name = Symbols::New(ctor_name);
+  ctor_name = Symbols::FromConcat(ctor_name, Symbols::Dot());
   // To indicate that this is an implicit constructor, we set the
   // token position and end token position of the function
   // to the token position of the class.
@@ -11677,8 +11675,7 @@ AstNode* Parser::ParseClosurization(AstNode* primary) {
   if (is_setter_name) {
     extractor_name = String::Concat(Symbols::SetterPrefix(), extractor_name);
   }
-  extractor_name = String::Concat(Symbols::HashMark(), extractor_name);
-  extractor_name = Symbols::New(extractor_name);
+  extractor_name = Symbols::FromConcat(Symbols::HashMark(), extractor_name);
   return new(Z) InstanceGetterNode(property_pos, primary, extractor_name);
 }
 
@@ -13044,9 +13041,10 @@ static String& BuildConstructorName(const String& type_class_name,
   // unnamed constructor for class 'A' is labeled 'A.'.
   // This convention prevents users from explicitly calling constructors.
   String& constructor_name =
-      String::Handle(String::Concat(type_class_name, Symbols::Dot()));
+      String::Handle(Symbols::FromConcat(type_class_name, Symbols::Dot()));

[hausner, 2015/08/20 21:45:46]

Isn't it premature to create a symbol here? If it's a named constructor, we
create and canonicalize a string that isn't going to be used.

[srdjan, 2015/08/20 22:11:18]

Discussed offline, agreed to keep it as it is, otherwise new strings would be
allocated repeatedly. We also need this in order to prevent allocation in new
space (optimizing compiler in helper thread)

   if (named_constructor != NULL) {
-    constructor_name = String::Concat(constructor_name, *named_constructor);
+    constructor_name =
+        Symbols::FromConcat(constructor_name, *named_constructor);
   }
   return constructor_name;
 }
@@ -13663,8 +13661,7 @@ AstNode* Parser::ParsePrimary() {
           // field access.
           String& qualified_name = String::ZoneHandle(Z, prefix.name());
           qualified_name = String::Concat(qualified_name, Symbols::Dot());
-          qualified_name = String::Concat(qualified_name, ident);
-          qualified_name = Symbols::New(qualified_name);
+          qualified_name = Symbols::FromConcat(qualified_name, ident);
           InvocationMirror::Type call_type =
               CurrentToken() == Token::kLPAREN ?
                   InvocationMirror::kMethod : InvocationMirror::kGetter;
@@ -13680,8 +13677,7 @@ AstNode* Parser::ParsePrimary() {
         // primary != NULL.
         String& qualified_name = String::ZoneHandle(Z, prefix.name());
         qualified_name = String::Concat(qualified_name, Symbols::Dot());
-        qualified_name = String::Concat(qualified_name, ident);
-        qualified_name = Symbols::New(qualified_name);
+        qualified_name = Symbols::FromConcat(qualified_name, ident);
         InvocationMirror::Type call_type =
             CurrentToken() == Token::kLPAREN ?
                 InvocationMirror::kMethod : InvocationMirror::kGetter;