Speed up freelist by using intrinsics to find last set bit.

runtime/vm/bit_set_test.cc

Index: runtime/vm/bit_set_test.cc
===================================================================
--- runtime/vm/bit_set_test.cc	(revision 0)
+++ runtime/vm/bit_set_test.cc	(revision 0)
@@ -0,0 +1,51 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "platform/assert.h"
+#include "vm/bit_set.h"
+#include "vm/unit_test.h"
+
+namespace dart {
+
+template<intptr_t Size>
+void TestBitSet() {
+  BitSet<Size> set;
+  EXPECT_EQ(-1, set.Last());
+  for (int i = 0; i < Size; ++i) {
+    EXPECT_EQ(false, set.Test(i));
+    set.Set(i, true);
+    EXPECT_EQ(true, set.Test(i));
+    EXPECT_EQ(i, set.Last());
+    for (int j = 0; j < Size; ++j) {
+      intptr_t next = set.Next(j);
+      if (j <= i) {
+        EXPECT_EQ(i, next);
+      } else {
+        EXPECT_EQ(-1, next);
+      }
+    }
+    set.Set(i, false);
+    EXPECT_EQ(false, set.Test(i));
+  }
+  set.Reset();
+  for (int i = 0; i < Size - 1; ++i) {
+    set.Set(i, true);
+    for (int j = i + 1; j < Size; ++j) {
+      set.Set(j, true);
+      EXPECT_EQ(j, set.Last());
+      EXPECT_EQ(i, set.ClearLastAndFindPrevious(j));
+      EXPECT_EQ(false, set.Test(j));
+    }
+  }
+}
+
+
+TEST_CASE(BitSetBasic) {
+  TestBitSet<8>();
+  TestBitSet<42>();
+  TestBitSet<128>();
+  TestBitSet<200>();
+}
+
+}  // namespace dart