Use SAR for positive divident by a power-of two constant divisor.

tests/language/div_with_power_of_two_test.dart

Index: tests/language/div_with_power_of_two_test.dart
===================================================================
--- tests/language/div_with_power_of_two_test.dart	(revision 0)
+++ tests/language/div_with_power_of_two_test.dart	(revision 0)
@@ -0,0 +1,58 @@
+// Copyright (c) 2013, 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.
+// Test division by power of two.
+// Test that results before and after optimization are the same.
+
+class TestValue {
+  final int argument;
+  final int result;
+  final Function function;
+  TestValue(func, arg) : function = func, argument = arg, result = func(arg) {}

[Florian Schneider, 2013/02/04 13:04:03]

How do you prevent func from already being optimized at this point? If
optimization_threshold changes, or just adding more test cases may break this
test.

Unfortunately I don't know a good way of generating tests like this in Dart.
Dynamic code generation would help greatly here.

So I think the only reliable way is to list all expected results as constants.

[srdjan, 2013/02/04 19:02:33]

Added expected values as well.

+}
+
+
+divBy4(a) => a ~/ 4;
+divByNeg4(a) => a ~/ - 4;

[Florian Schneider, 2013/02/04 13:04:03]

Remove extra space after -

/s/- 4/-4/

[srdjan, 2013/02/04 19:02:33]

Done.

+divBy134217728(a) => a ~/ 134217728;
+divByNeg134217728(a) => a ~/ -134217728;
+

[Florian Schneider, 2013/02/04 13:04:03]

Please add tests for the special cases:

a ~/ 0
a ~/ 1
a ~/ -1
a ~/ 2
a ~/ -2

[srdjan, 2013/02/04 19:02:33]

Done.

+divBy4_(a) => a ~/ 4;
+divByNeg4_(a) => a ~/ - 4;

[Florian Schneider, 2013/02/04 13:04:03]

/s/- 4/-4/

[srdjan, 2013/02/04 19:02:33]

Done.

+divBy549755813888(a) => a ~/ 549755813888;
+divByNeg549755813888(a) => a ~/ -549755813888;
+
+
+test(dividends, testFunctions) {
+  var tests = new List();
+  for (Function f in testFunctions) {
+    for (int d in dividends) {
+      tests.add(new TestValue(f, d));
+    }
+  }
+  // Optimize.
+  for (int i = 0; i < 10000; i++) {
+    for (var f in testFunctions) {
+      f(10);
+    }
+  }
+
+  for (var t in tests) {
+    Expect.equals(t.result, t.function(t.argument));
+  }
+}
+
+
+main() {
+  // 32 bits.
+  var dividends = const [134217730, -134217730, 10, -10];
+  var testFunctions = const [divBy4, divByNeg4,
+      divBy134217728, divByNeg134217728];
+  test(dividends, testFunctions);
+  // 64 bits, use different functions, 64 bit arguments.
+  dividends = const [549755813990, -549755813990,
+      288230925907525632, -288230925907525632];
+  testFunctions = const [divBy4_, divByNeg4_,
+      divBy549755813888, divByNeg549755813888];
+  test(dividends, testFunctions);
+}