Implement simple dead store elimination.

tests/language/vm/store_elimination_vm_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.
+// Test correctness of side effects tracking used by load to load forwarding.
+
+// VMOptions=--optimization-counter-threshold=10
+
+import "package:expect/expect.dart";
+
+class C {
+  var x;
+  var y;
+  final z = 123;
+}
+
+class D {
+  var x = 0.0;
+}
+
+var array = [0, 0];
+
+s1(a) {
+  a.x = 42;
+  a.x = 43;
+  return a.x;
+}
+
+void foo(a) {
+  Expect.equals(42, a.x);
+}
+
+s1a(a) {
+  a.x = 42;
+  foo(a);
+  a.x = 43;
+  return a.x;
+}
+
+s2() {
+  var t = new C();
+  return t;
+}
+
+s3(a, b) {
+  a.x = b + 1;
+  if (b % 2 == 0) {
+    a.x = 0;
+  } else {
+    a.x = 0;
+  }
+  return a.x;
+}
+
+s4(a, b) {
+  a.x = b + 1.0;
+  if (b % 2 == 0) {
+    a.x = b + 2.0;
+  }
+  a.x = b + 1.0;
+  return a.x;
+}
+
+test_with_context() {
+  f(a) {
+    var b = a + 1;
+    return (() => b + 1)();
+  }
+  for (var i = 0; i < 100000; i++) f(42);
+  Expect.equals(44, f(42));
+}
+
+test_with_instance() {
+  for (var i = 0; i < 20; i++) Expect.equals(43, s1(new C()));
+  for (var i = 0; i < 20; i++) Expect.equals(43, s1a(new C()));
+  for (var i = 0; i < 20; i++) Expect.equals(123, s2().z);
+  for (var i = 0; i < 20; i++) Expect.equals(0, s3(new C(), i));
+  for (var i = 0; i < 20; i++) Expect.equals(i + 1.0, s4(new D(), i));
+}
+
+arr1(a) {
+  a[0] = 42;
+  a[0] = 43;
+  Expect.equals(a[0], 43);
+  return a[0];
+}
+
+arr2(a, b) {
+  a[0] = 42;
+  a[b % 2] = 43;
+  Expect.equals(a[b % 2], 43);
+  return a[0];
+}
+
+test_with_array() {
+  for (var i = 0; i < 20; i++) Expect.equals(43, arr1(array));
+  for (var i = 0; i < 20; i++) {
+    Expect.equals(i % 2 == 0 ? 43 : 42, arr2(array, i));
+  }
+}
+
+var st = 0;
+
+static1(b) {
+  st = 42;
+  if (b % 2 == 0) {
+    st = 2;
+  }
+  st = b + 1;
+  Expect.equals(st, b + 1);
+  return st;
+}
+
+test_with_static() {
+  for (var i = 0; i < 20; i++) Expect.equals(i + 1, static1(i));
+}
+
+main() {
+  test_with_instance();
+  test_with_array();
+  test_with_context();
+  test_with_static();
+}