Recognize pattern (a << b) & c with c being a positive Smi and allow left shift to truncate the res…

tests/standalone/left_shift_bit_and_op_test.dart

+// 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.
+//
+// Tests optimizing (a << b) & c if c is a Smi constant.
+
+main() {
+  checkshiftAnd32();
+  checkShiftAnd64();
+  // Optimize shiftAnd32.
+  for (int i = 0; i < 10000; i++) {
+    A.shiftAnd32(12, 17);
+    A.shiftAnd64(12, 17);
+  }
+  checkshiftAnd32();
+  checkShiftAnd64();
+
+  Expect.throws(() => A.shiftAnd32(12, -5));
+}
+
+
+checkshiftAnd32() {
+  Expect.equals(1572864, A.shiftAnd32(12, 17));
+  Expect.equals(12, A.shiftAnd32(12, 0));
+  Expect.equals(285212672, A.shiftAnd32(16779392, 17));
+}
+
+
+checkShiftAnd64() {
+  Expect.equals(1125936481173504, A.shiftAnd64(4611694814806147072, 7));
+}
+
+
+class A {

[Vyacheslav Egorov (Google), 2013/02/20 00:37:06]

Please add a test that tests when (a << c) has multiple uses (one test for
normal ones, one test for environment ones).

+  static const int MASK_32 = (1 << 30) - 1;
+  static const int MASK_64 = (1 << 62) - 1;
+
+  static shiftAnd32(a, c) {
+    return (a << c) & MASK_32;
+  }
+
+  static shiftAnd64(a, c) {
+    return (a << c) & MASK_64;
+  }
+}