[v8-dev] Speed up join on arrays. (issue457021)

[erik . corry]

Reviewers: Mads Ager,

Description:
Speed up join on arrays.

Please review this at http://codereview.chromium.org/457021

SVN Base: http://v8.googlecode.com/svn/branches/bleeding_edge/

Affected files:
   M     src/array.js


Index: src/array.js
===================================================================
--- src/array.js        (revision 3389)
+++ src/array.js        (working copy)
@@ -77,7 +77,8 @@
      var key = keys[i];
      if (key != last_key) {
        var e = array[key];
-      builder.add(convert(e));
+      if (typeof(e) !== 'string') e = convert(e);
+      builder.add(e);
        last_key = key;
      }
    }
@@ -114,18 +115,37 @@
      if (length == 1) {
        var e = array[0];
        if (!IS_UNDEFINED(e) || (0 in array)) {
+        if (typeof(e) === 'string') return e;
          return convert(e);
        }
      }

      var builder = new StringBuilder();

-    for (var i = 0; i < length; i++) {
-      var e = array[i];
-      if (i != 0) builder.add(separator);
-      if (!IS_UNDEFINED(e) || (i in array)) {
-        builder.add(convert(e));
+    // We pull the empty separator check outside the loop for speed!
+    if (separator.length == 0) {
+      for (var i = 0; i < length; i++) {
+        var e = array[i];
+        if (!IS_UNDEFINED(e) || (i in array)) {
+          if (typeof(e) !== 'string') e = convert(e);
+          if (e.length > 0) {
+            var elements = builder.elements;
+            elements[elements.length] = e;
+          }
+        }
        }
+    } else {
+      for (var i = 0; i < length; i++) {
+        var e = array[i];
+        if (i != 0) builder.add(separator);
+        if (!IS_UNDEFINED(e) || (i in array)) {
+          if (typeof(e) !== 'string') e = convert(e);
+          if (e.length > 0) {
+            var elements = builder.elements;
+            elements[elements.length] = e;
+          }
+        }
+      }
      }
      return builder.generate();
    } finally {
@@ -136,12 +156,14 @@


  function ConvertToString(e) {
+  if (typeof(e) === 'string') return e;
    if (e == null) return '';
    else return ToString(e);
  }


  function ConvertToLocaleString(e) {
+  if (typeof(e) === 'string') return e;
    if (e == null) return '';
    else {
      // e_obj's toLocaleString might be overwritten, check if it is a  
function.


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