implement bulk re-exports for instantiate setter perf

Author: guybedford

src/codegeneration/InstantiateModuleTransformer.js

@@ -349,29 +349,31 @@ export class InstantiateModuleTransformer extends ModuleTransformer {
 
       // then do export bindings of re-exported dependencies
       if (externalExportBindings) {
+        let reexports = Object.create(null);
         externalExportBindings.forEach(({exportName, importName}) => {
-          let statement = importName === null ?
-              parseStatement `$__export(${exportName}, $__m);` :
-              parseStatement `$__export(${exportName}, $__m.${importName});`;
-          setterStatements.push(statement);
+          reexports[exportName] = importName === null ?
+              parseExpression `$__m` : parseExpression `$__m.${importName}`;
         });
+        setterStatements.push(
+            parseStatement `$__export(${createObjectLiteral(reexports)})`);
       }
 
       // create local module bindings
       if (moduleBinding) {
         setterStatements.push(
-          parseStatement `${id(moduleBinding)} = $__m;`
-        );
+            parseStatement `${id(moduleBinding)} = $__m;`);
       }
 
       // finally run export * if applying to this dependency, for not-already
       // exported dependencies
       if (exportStarBinding) {
         setterStatements = setterStatements.concat(parseStatements `
+          var exportObj = Object.create(null);
           Object.keys($__m).forEach(function(p) {
             if (p !== 'default' && !$__exportNames[p])
-              $__export(p, $__m[p]);
+              exportObj[p] = $__m[p];
           });
+          $__export(exportObj);
         `);
 
         let exportNames = {};

third_party/es6-module-loader/loader.js

@@ -687,7 +687,16 @@ function logloads(loads) {
         // NB This should be an Object.defineProperty, but that is very slow.
         //    By disaling this module write-protection we gain performance.
         //    It could be useful to allow an option to enable or disable this.
-        moduleObj[name] = value;
+
+        // bulk export object
+        if (typeof name == 'object') {
+          for (var p in name)
+            moduleObj[p] = name[p];
+        }
+        // single export name / value pair
+        else {
+          moduleObj[name] = value;
+        }
 
         for (var i = 0, l = module.importers.length; i < l; i++) {
           var importerModule = module.importers[i];