Cache template literal callSiteObj

src/harmony-templates.js

 // 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.
 
 'use strict';
 
-function GetTemplateCallSite(siteObj, rawStrings) {
-  // TODO(caitp): ensure same template callsite is used for subsequent tag calls
+var callSiteCache = new $Map;
+
+function SameCallSiteElements(rawStrings, other) {
+  var length = rawStrings.length;
+  var other = other.raw;
+
+  if (length !== other.length) return false;
+
+  for (var i = 0; i < length; ++i) {
+    if (rawStrings[i] !== other[i]) return false;
+  }
+
+  return true;
+}
+
+
+function GetCachedCallSite(siteObj, hash) {
+  var obj = %MapGet(callSiteCache, hash);
+
+  if (IS_UNDEFINED(obj)) return;
+
+  var length = obj.length;
+  for (var i = 0; i < length; ++i) {
+    if (SameCallSiteElements(siteObj, obj[i])) return obj[i];
+  }
+}
+
+
+function SetCachedCallSite(siteObj, hash) {
+  var obj = %MapGet(callSiteCache, hash);
+
+  if (IS_UNDEFINED(obj)) {
+    %MapSet(callSiteCache, hash, new InternalArray(siteObj));

[arv (Not doing code reviews), 2014/11/19 21:38:57]

Lets not use the strange overloading of params for the array constructor.

var array = new InternalArray(1);
array[0] = siteObj;

+  } else {
+    // Unlikely hash collision case.
+    obj.push(siteObj);
+  }
+
+  return siteObj;
+}
+
+
+function GetTemplateCallSite(siteObj, rawStrings, hash) {
+  var cached = GetCachedCallSite(rawStrings, hash);
+
+  if (!IS_UNDEFINED(cached)) return cached;
 
   %AddNamedProperty(siteObj, "raw", %ObjectFreeze(rawStrings),
       READ_ONLY | DONT_ENUM | DONT_DELETE);
 
-  return %ObjectFreeze(siteObj);
+  return SetCachedCallSite(%ObjectFreeze(siteObj), hash);
 }
 
 
 // ES6 Draft 10-14-2014, section 21.1.2.4
 function StringRaw(callSite) {
   // TODO(caitp): Use rest parameters when implemented
   var numberOfSubstitutions = %_ArgumentsLength();
   var cooked = ToObject(callSite);
   var raw = ToObject(cooked.raw);
   var literalSegments = ToLength(raw.length);
@@ skipping 15 matching lines @@
 function ExtendStringForTemplates() {
   %CheckIsBootstrapping();
 
   // Set up the non-enumerable functions on the String object.
   InstallFunctions($String, DONT_ENUM, $Array(
     "raw", StringRaw
   ));
 }
 
 ExtendStringForTemplates();