Replace PushIfAbsent by a Stack object

src/js/array.js

Index: src/js/array.js
diff --git a/src/js/array.js b/src/js/array.js
index 1468d57c6cae52f3f4c307609d1c58a9517382f5..6d647bf275a0c8ffa6c7f63f892ecd085ee49f14 100644
--- a/src/js/array.js
+++ b/src/js/array.js
@@ -74,11 +74,6 @@ function DefineIndexedProperty(array, i, value) {
 }
 
 
-// Global list of arrays visited during toString, toLocaleString and
-// join invocations.
-var visited_arrays = new InternalArray();
-
-
 // Gets a sorted array of array keys.  Useful for operations on sparse
 // arrays.  Dupes have not been removed.
 function GetSortedArrayKeys(array, indices) {
@@ -150,6 +145,17 @@ function SparseJoin(array, len, convert) {
 }
 
 
+function StringBuilderJoin(elements, length, separator) {
+  length = MinSimple(elements.length, length);
+  if (length == 0) return "";
+  var result = elements[0];
+  for (var i = 1; i < length; i++) {
+    result = result + separator + elements[i];
+  }
+  return result;
+}
+
+
 function UseSparseVariant(array, length, is_array, touched) {
   // Only use the sparse variant on arrays that are likely to be sparse and the
   // number of elements touched in the operation is relatively small compared to
@@ -167,6 +173,31 @@ function UseSparseVariant(array, length, is_array, touched) {
     (touched > estimated_elements * 4);
 }
 
+function Stack() {
+  this.length = 0;

[adamk, 2016/03/10 19:34:05]

As Toon mentioned, this is indeed the problematic bit: you can't write to
'length' and 'values' here since they could trigger setters on Object.prototype.

+  this.values = new InternalArray();
+}
+
+function StackPush(stack, value) {
+  stack.values[stack.length++] = value;
+}
+
+function StackPop(stack) {
+  stack.values[--stack.length] = null
+}
+
+function StackHas(stack, v) {
+  var length = stack.length;
+  var values = stack.values;
+  for (var i = 0; i < length; i++) {
+    if (values[i] === v) return true;
+  }
+  return false;
+}
+
+// Global list of arrays visited during toString, toLocaleString and
+// join invocations.
+var visited_arrays = new Stack();
 
 function Join(array, length, separator, convert) {
   if (length == 0) return '';
@@ -176,7 +207,8 @@ function Join(array, length, separator, convert) {
   if (is_array) {
     // If the array is cyclic, return the empty string for already
     // visited arrays.
-    if (!%PushIfAbsent(visited_arrays, array)) return '';
+    if (StackHas(visited_arrays, array)) return '';
+    StackPush(visited_arrays, array);
   }
 
   // Attempt to convert the elements.
@@ -235,11 +267,11 @@ function Join(array, length, separator, convert) {
         elements[i] = e;
       }
     }
-    return %StringBuilderJoin(elements, length, separator);
+    return StringBuilderJoin(elements, length, separator);
   } finally {
     // Make sure to remove the last element of the visited array no
     // matter what happens.
-    if (is_array) visited_arrays.length = visited_arrays.length - 1;
+    if (is_array) StackPop(visited_arrays);
   }
 }
 
@@ -1959,6 +1991,10 @@ utils.Export(function(to) {
   to.InnerArraySort = InnerArraySort;
   to.InnerArrayToLocaleString = InnerArrayToLocaleString;
   to.PackedArrayReverse = PackedArrayReverse;
+  to.Stack = Stack;
+  to.StackHas = StackHas;
+  to.StackPush = StackPush;
+  to.StackPop = StackPop;
 });
 
 %InstallToContext([