Optimize new TypedArray(typedArray) constructor

src/js/typedarray.js

 // Copyright 2013 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.
 
 (function(global, utils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 182 matching lines @@
   }
   var byteLength = l * ELEMENT_SIZE;
   if (byteLength > %_TypedArrayMaxSizeInHeap()) {
     var buffer = new GlobalArrayBuffer(byteLength);
     %_TypedArrayInitialize(obj, ARRAY_ID, buffer, 0, byteLength, true);
   } else {
     %_TypedArrayInitialize(obj, ARRAY_ID, null, 0, byteLength, true);
   }
 }
 
-function NAMEConstructByArrayLike(obj, arrayLike) {
-  var length = arrayLike.length;
+function NAMEConstructByArrayLike(obj, arrayLike, length) {
   var l = ToPositiveInteger(length, kInvalidTypedArrayLength);
 
   if (l > %_MaxSmi()) {
     throw MakeRangeError(kInvalidTypedArrayLength);
   }
   var initialized = false;
   var byteLength = l * ELEMENT_SIZE;
   if (byteLength <= %_TypedArrayMaxSizeInHeap()) {
     %_TypedArrayInitialize(obj, ARRAY_ID, null, 0, byteLength, false);
   } else {
@@ skipping 19 matching lines @@
   var iterator = %_Call(iteratorFn, iterable);
   var newIterable = {
     __proto__: null
   };
   // TODO(littledan): Computed properties don't work yet in nosnap.
   // Rephrase when they do.
   newIterable[iteratorSymbol] = function() { return iterator; }
   for (var value of newIterable) {
     list.push(value);
   }
-  NAMEConstructByArrayLike(obj, list);
+  NAMEConstructByArrayLike(obj, list, list.length);
 }
 
 // ES#sec-typedarray-typedarray TypedArray ( typedArray )
 function NAMEConstructByTypedArray(obj, typedArray) {
   // TODO(littledan): Throw on detached typedArray
   var srcData = %TypedArrayGetBuffer(typedArray);
   var length = %_TypedArrayGetLength(typedArray);
   var byteLength = %_ArrayBufferViewGetByteLength(typedArray);
   var newByteLength = length * ELEMENT_SIZE;
+  NAMEConstructByArrayLike(obj, typedArray, length);
   var bufferConstructor = SpeciesConstructor(srcData, GlobalArrayBuffer);
-  var data = new GlobalArrayBuffer(newByteLength);
   var prototype = bufferConstructor.prototype;
   // TODO(littledan): Use the right prototype based on bufferConstructor's realm
   if (IS_RECEIVER(prototype) && prototype !== GlobalArrayBufferPrototype) {
-    %InternalSetPrototype(data, prototype);
-  }
-  %_TypedArrayInitialize(obj, ARRAY_ID, data, 0, newByteLength, true);
-  // Note: The separate CloneArrayBuffer path in the spec ensures
-  // that NaNs are not canonicalized, but because V8 does not
-  // canonicalize NaNs, we do not have to do anything different.
-  // TODO(littledan): Make a fastpath based on memcpy
-  for (var i = 0; i < length; i++) {
-    obj[i] = typedArray[i];
+    %InternalSetPrototype(%TypedArrayGetBuffer(obj), prototype);
   }
 }
 
 function NAMEConstructor(arg1, arg2, arg3) {
   if (!IS_UNDEFINED(new.target)) {
     if (IS_ARRAYBUFFER(arg1) || IS_SHAREDARRAYBUFFER(arg1)) {
       NAMEConstructByArrayBuffer(this, arg1, arg2, arg3);
     } else if (IS_NUMBER(arg1) || IS_STRING(arg1) ||
                IS_BOOLEAN(arg1) || IS_UNDEFINED(arg1)) {
       NAMEConstructByLength(this, arg1);
     } else if (IS_TYPEDARRAY(arg1)) {
       NAMEConstructByTypedArray(this, arg1);
     } else {
       var iteratorFn = arg1[iteratorSymbol];
-      if (IS_UNDEFINED(iteratorFn) || iteratorFn === ArrayValues) {
-        NAMEConstructByArrayLike(this, arg1);
+      if (IS_UNDEFINED(iteratorFn)) {
+        NAMEConstructByArrayLike(this, arg1, arg1.length);
       } else {
         NAMEConstructByIterable(this, arg1, iteratorFn);
       }
     }
   } else {
     throw MakeTypeError(kConstructorNotFunction, "NAME")
   }
 }
 
 // TODO(littledan): Remove this performance workaround BUG(chromium:579905)
@@ skipping 712 matching lines @@
   "setUint32", DataViewSetUint32JS,
 
   "getFloat32", DataViewGetFloat32JS,
   "setFloat32", DataViewSetFloat32JS,
 
   "getFloat64", DataViewGetFloat64JS,
   "setFloat64", DataViewSetFloat64JS
 ]);
 
 })