dart2js: Optimize Function.apply for 0-3 argument calls.

sdk/lib/_internal/compiler/js_lib/js_helper.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library _js_helper;
 
 import 'dart:_async_await_error_codes' as async_error_codes;
 
 import 'dart:_js_embedded_names' show
     DEFERRED_LIBRARY_URIS,
@@ skipping 1128 matching lines @@
     // specialization.
     return namedArguments == null
         ? applyFunctionWithPositionalArguments(
             function, positionalArguments)
         : applyFunctionWithNamedArguments(
             function, positionalArguments, namedArguments);
   }
 
   static applyFunctionWithPositionalArguments(Function function,
                                               List positionalArguments) {
-    int argumentCount = 0;
     List arguments;
 
     if (positionalArguments != null) {
       if (JS('bool', '# instanceof Array', positionalArguments)) {
-        arguments = positionalArguments;
+        arguments = JS('JSArray', '#', positionalArguments);
       } else {
         arguments = new List.from(positionalArguments);
       }
-      argumentCount = JS('int', '#.length', arguments);
     } else {
       arguments = [];
     }
 
+    if (arguments.length == 0) {
+      String selectorName = JS_GET_NAME(JsGetName.CALL_PREFIX0);
+      if (JS('bool', '!!#[#]', function, selectorName)) {
+        return JS('', '#[#]()', function, selectorName);
+      }
+    } else if (arguments.length == 1) {
+      String selectorName = JS_GET_NAME(JsGetName.CALL_PREFIX1);
+      if (JS('bool', '!!#[#]', function, selectorName)) {
+        return JS('', '#[#](#)', function, selectorName, arguments[0]);
+      }
+    } else if (arguments.length == 2) {
+      String selectorName = JS_GET_NAME(JsGetName.CALL_PREFIX2);
+      if (JS('bool', '!!#[#]', function, selectorName)) {
+        return JS('', '#[#](#,#)', function, selectorName,
+            arguments[0], arguments[1]);
+      }
+    } else if (arguments.length == 3) {
+      String selectorName = JS_GET_NAME(JsGetName.CALL_PREFIX3);
+      if (JS('bool', '!!#[#]', function, selectorName)) {
+        return JS('', '#[#](#,#,#)', function, selectorName,
+            arguments[0], arguments[1], arguments[2]);

[sra1, 2015/03/25 03:16:29]

I would not surprise me if the array bounds checks were not optimized.
Running with --trust-primitives would be misleading.
Safer to use:

JS('', '#[#](#[0],#[1],#[2])', function, selectorName,
  arguments, arguments, arguments);

[floitsch, 2015/03/25 22:58:30]

I was sure I had tested it, but you are (unfortunately) right.
done.

+      }
+    }
+    return _genericApplyFunctionWithPositionalArguments(function, arguments);
+  }
+
+  static _genericApplyFunctionWithPositionalArguments(Function function,
+                                                      List arguments) {
+    int argumentCount = arguments.length;
     String selectorName =
         '${JS_GET_NAME(JsGetName.CALL_PREFIX)}\$$argumentCount';
     var jsFunction = JS('var', '#[#]', function, selectorName);
     if (jsFunction == null) {
       var interceptor = getInterceptor(function);
       jsFunction = JS('', '#["call*"]', interceptor);
 
       if (jsFunction == null) {
-        return functionNoSuchMethod(function, positionalArguments, null);
+        return functionNoSuchMethod(function, arguments, null);
       }
       ReflectionInfo info = new ReflectionInfo(jsFunction);
       int maxArgumentCount = info.requiredParameterCount +
           info.optionalParameterCount;
       if (info.areOptionalParametersNamed || maxArgumentCount < argumentCount) {
-        return functionNoSuchMethod(function, positionalArguments, null);
+        return functionNoSuchMethod(function, arguments, null);
       }
       arguments = new List.from(arguments);
       for (int pos = argumentCount; pos < maxArgumentCount; pos++) {
         arguments.add(info.defaultValue(pos));
       }
     }
     // We bound 'this' to [function] because of how we compile
     // closures: escaped local variables are stored and accessed through
     // [function].
     return JS('var', '#.apply(#, #)', jsFunction, function, arguments);
@@ skipping 2693 matching lines @@
   // This is a function that will return a helper function that does the
   // iteration of the sync*.
   //
   // Each invocation should give a body with fresh state.
   final dynamic /* js function */ _outerHelper;
 
   SyncStarIterable(this._outerHelper);
 
   Iterator get iterator => new SyncStarIterator(JS('', '#()', _outerHelper));
 }