Object.observe: change array truncation logic to efficiently handle large sparse arrays

test/mjsunit/harmony/object-observe.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 608 matching lines @@
 }
 
 
 // Observing array length (including truncation)
 reset();
 var arr = ['a', 'b', 'c', 'd'];
 var arr2 = ['alpha', 'beta'];
 var arr3 = ['hello'];
 arr3[2] = 'goodbye';
 arr3.length = 6;
-// TODO(adamk): Enable this test case when it can run in a reasonable
-// amount of time.
-//var slow_arr = new Array(1000000000);
-//slow_arr[500000000] = 'hello';
+var slow_arr = new Array(1000000000);
+slow_arr[500000000] = 'hello';
 Object.defineProperty(arr, '0', {configurable: false});
 Object.defineProperty(arr, '2', {get: function(){}});
 Object.defineProperty(arr2, '0', {get: function(){}, configurable: false});
 Object.observe(arr, observer.callback);
 Object.observe(arr2, observer.callback);
 Object.observe(arr3, observer.callback);
+Object.observe(slow_arr, observer.callback);
 arr.length = 2;
 arr.length = 0;
 arr.length = 10;
 Object.defineProperty(arr, 'length', {writable: false});
 arr2.length = 0;
 arr2.length = 1; // no change expected
 Object.defineProperty(arr2, 'length', {value: 1, writable: false});
 arr3.length = 0;
 ++arr3.length;
 arr3.length++;
 arr3.length /= 2;
 Object.defineProperty(arr3, 'length', {value: 5});
 Object.defineProperty(arr3, 'length', {value: 10, writable: false});
+slow_arr.length = 100;
 Object.deliverChangeRecords(observer.callback);
 observer.assertCallbackRecords([
   { object: arr, name: '3', type: 'deleted', oldValue: 'd' },
   { object: arr, name: '2', type: 'deleted' },
   { object: arr, name: 'length', type: 'updated', oldValue: 4 },
   { object: arr, name: '1', type: 'deleted', oldValue: 'b' },
   { object: arr, name: 'length', type: 'updated', oldValue: 2 },
   { object: arr, name: 'length', type: 'updated', oldValue: 1 },
   { object: arr, name: 'length', type: 'reconfigured', oldValue: 10 },
   { object: arr2, name: '1', type: 'deleted', oldValue: 'beta' },
   { object: arr2, name: 'length', type: 'updated', oldValue: 2 },
   { object: arr2, name: 'length', type: 'reconfigured', oldValue: 1 },
   { object: arr3, name: '2', type: 'deleted', oldValue: 'goodbye' },
   { object: arr3, name: '0', type: 'deleted', oldValue: 'hello' },
   { object: arr3, name: 'length', type: 'updated', oldValue: 6 },
   { object: arr3, name: 'length', type: 'updated', oldValue: 0 },
   { object: arr3, name: 'length', type: 'updated', oldValue: 1 },
   { object: arr3, name: 'length', type: 'updated', oldValue: 2 },
   { object: arr3, name: 'length', type: 'updated', oldValue: 1 },
   { object: arr3, name: 'length', type: 'reconfigured', oldValue: 5 },
+  { object: slow_arr, name: '500000000', type: 'deleted', oldValue: 'hello' },
+  { object: slow_arr, name: 'length', type: 'updated', oldValue: 1000000000 },
 ]);
 
 
 // Assignments in loops (checking different IC states).
 reset();
 var obj = {};
 Object.observe(obj, observer.callback);
 for (var i = 0; i < 5; i++) {
   obj["a" + i] = i;
 }
@@ skipping 363 matching lines @@
     for (var n1 = 0; n1 < 3; ++n1)
       for (var n2 = 0; n2 < 3; ++n2)
         for (var i in mutation)
           TestFastElementsLength(mutation[i], b1 != 0, b2 != 0, 20*n1, 20*n2);
 
 for (var b1 = 0; b1 < 2; ++b1)
   for (var b2 = 0; b2 < 2; ++b2)
     for (var n = 0; n < 3; ++n)
       for (var i in mutationByIncr)
         TestFastElementsLength(mutationByIncr[i], b1 != 0, b2 != 0, 7*n, 7*n+1);