Issue 5063 - [emscripten] Make FilterNotifier calls more efficient

compiled/bindings.ipp

Index: compiled/bindings.ipp
===================================================================
--- a/compiled/bindings.ipp
+++ b/compiled/bindings.ipp
@@ -455,25 +455,19 @@ namespace bindings_internal
 
       auto it = classes.find(call.pointerType);
       if (it == classes.end())
         throw std::runtime_error("Function " + std::string(call.name) + " returns pointer to unknown class");
 
       const ClassInfo& cls = it->second;
       auto offset = cls.subclass_differentiator.offset;
       if (offset == SIZE_MAX)
-        result += "    result = " + cls.name + "(result);\n";
+        result += "    result = exports." + cls.name + "(result);\n";
       else
-      {
-        result += "    var type = HEAP32[result + " + std::to_string(offset)+ " >> 2];\n";
-        result += "    if (type in " + cls.name + "_mapping)\n";
-        result += "      result = new (exports[" + cls.name + "_mapping[type]])(result);\n";
-        result += "    else\n";
-        result += "      throw new Error('Unexpected " + cls.name + " type: ' + type);\n";
-      }
+        result += "    result = exports." + cls.name + ".fromPointer(result);\n";
 
       result += "  }\n";
       result += "  else\n";
       result += "    result = null;\n";
       return result;
     }
     else
       throw std::runtime_error("Unexpected return type for " + std::string(call.name));
@@ -586,29 +580,44 @@ namespace bindings_internal
         };
         return result;
       }
     )");
   }
 
   void printClass(const ClassInfo& cls)
   {
+    printf("exports.%s = createClass(%s, %i);\n", cls.name.c_str(),
+        (cls.baseClass ? ("exports." + cls.baseClass->name).c_str() : "null"),
+        cls.ref_counted_offset);
+
     DifferentiatorInfo differentiator = cls.subclass_differentiator;
     if (differentiator.offset != SIZE_MAX)
     {
       printf("var %s_mapping = \n", cls.name.c_str());
       puts("{");
       for (const auto& item : differentiator.mapping)
         printf("  %i: '%s',\n", item.first, item.second.c_str());
       puts("};");
-    }
 
-    printf("exports.%s = createClass(%s, %i);\n", cls.name.c_str(),
-        (cls.baseClass ? ("exports." + cls.baseClass->name).c_str() : "null"),
-        cls.ref_counted_offset);
+      printf("exports.%s.fromPointer = function(ptr)\n", cls.name.c_str());
+      puts("{");
+      printf("  var type = HEAP32[ptr + %i >> 2];\n", differentiator.offset);
+      printf("  if (type in %s_mapping)\n", cls.name.c_str());
+      printf("    return new (exports[%s_mapping[type]])(ptr);\n", cls.name.c_str());
+      printf("  throw new Error('Unexpected %s type: ' + type);\n", cls.name.c_str());
+      puts("};");
+    }
+    else
+    {
+      printf("exports.%s.fromPointer = function(ptr)\n", cls.name.c_str());
+      puts("{");
+      printf("  return new exports.%s(ptr);\n", cls.name.c_str());
+      puts("};");
+    }
 
     for (const auto& item : cls.properties)
     {
       printf("Object.defineProperty(exports.%s.prototype, '%s', {%s});\n",
           cls.name.c_str(), item.name.c_str(),
           generatePropertyDescriptor(item).c_str());
     }