Generalize bounds checks.

tests/standalone/array_bounds_check_generalization_test.dart

+// Copyright (c) 2012, 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.
+//
+// VMOptions=--optimization_counter_threshold=10 --no-use-osr
+
+import "package:expect/expect.dart";
+
+test1(a, start, step, N) {
+  var e;
+  for (var i = 0; i < N; i++) {

[Florian Schneider, 2014/10/07 11:40:48]

Can you add a test with a nested loop as well? e.g.

for (var i = 0; i < N; i++) {
  for (var j = 0; j < M; j++) {
    e += a[i * M + j]
  }
}

[Vyacheslav Egorov (Google), 2014/10/07 18:57:27]

Done

+    e = a[start + i * step];
+  }
+  return e;
+}
+
+test2(a, b) {
+  var e;
+  for (var i = 0, j = 0, k = 0; i < a.length; i++, j++, k++) {
+    e = b[k] = a[j];
+  }
+  return e;
+}
+
+test3(a, b) {
+  var e;
+  for (var i = 0, j = 1, k = 0; i < a.length - 1; i++, j++, k++) {
+    e = b[k] = a[j - 1];
+  }
+  return e;
+}
+
+test4(a, b) {
+  var e;
+  if (a.length < 2) {
+    return;
+  }
+
+  for (var i = 0, j = 1, k = 0; i < a.length - 1; i++, j++, k++) {
+    e = b[k] = a[j - 1];
+  }
+  return e;
+}
+
+test5(a, b, k0) {
+  var e;
+  if (a.length < 2) {
+    return;
+  }
+
+  if (k0 > 1) {
+    return;
+  }
+
+  for (var i = 0, j = 1, k = 0; i < a.length - 1; i++, j++, k++) {
+    e = b[k - k0] = a[j - 1];
+  }
+  return e;
+}
+
+main() {
+  var a = const [0, 1, 2, 3, 4, 5, 6, 7];
+  var b = new List(a.length);
+  for (var i = 0; i < 10000; i++) {
+    Expect.equals(a.last, test1(a, 0, 1, a.length));
+    Expect.equals(a.last, test2(a, b));
+    Expect.equals(a[a.length - 2], test3(a, b));
+    Expect.equals(a[a.length - 2], test4(a, b));
+    Expect.equals(a[a.length - 2], test5(a, b, 0));
+  }
+
+  test1(a, 0, 2, a.length ~/ 2);
+  Expect.throws(() => test1(a, 1, 1, a.length));
+  Expect.throws(() => test2(a, new List(a.length - 1)));
+}