Ensure newly allocated empty Arrays are transitioned to FAST_ELEMENT

test/mjsunit/elements-kind-fast-element-bias.js

+// Copyright 2011 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
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Flags: --allow-natives-syntax --smi-only-arrays
+
+support_smi_only_arrays = %HasFastSmiOnlyElements([1,2,3,4,5,6,7,8,9,10]);
+
+if (support_smi_only_arrays) {
+  print("Tests include smi-only arrays.");
+} else {
+  print("Tests do NOT include smi-only.");
+}
+
+// Ensure that there is a global bais for not aggressively transitioning Arrays

[Jakob Kummerow, 2012/01/04 20:55:17]

s/bais/bias/

Even better, re-word the comment. Maybe "Test that repeated SMI->FAST
transitions are avoided by initializing Arrays with FAST_ELEMENTS right away"?
And then I'd add the inverse of the check at the end before messing with the
bias:

if (support_smi_only_arrays) {
  assertTrue(%HasFastSmiOnlyElements(new Array()));
}

+// to FAST_ELEMENTs.
+// TODO(danno): Remove this code when bias for early ElementsKind transition is
+// tracked per allocation site and not globally.
+[1,2,3][0] = new Object();
+[1,2,3][0] = new Object();
+[1,2,3][0] = new Object();
+[1,2,3][0] = new Object();
+[1,2,3][0] = new Object();
+[1,2,3][0] = new Object();
+[1,2,3][0] = new Object();
+[1,2,3][0] = new Object();
+[1,2,3][0] = new Object();
+[1,2,3][0] = new Object();
+[1,2,3][0] = new Object();
+
+if (support_smi_only_arrays) {
+  assertTrue(%HasFastElements(new Array()));
+}