Refactor load forwarding pass to use a Place abstraction.

tests/language/load_to_load_forwarding_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.
 
 import "package:expect/expect.dart";
 import "dart:typed_data";
 
 class A {
   var x, y;
@@ skipping 33 matching lines @@
     return arr.length;  // Immutable length load.
   }
 
   if (arr.length < 2) {  // Mutable length load, should not be forwarded.
     arr.add(null);
   }
 
   return arr.length;
 }
 
-
 testPhiRepresentation(f, arr) {
   if (f) {
     arr[0] = arr[0] + arr[1];
   } else {
     arr[0] = arr[0] - arr[1];
   }
   return arr[0];
 }
 
-
 testPhiConvertions(f, arr) {
   if (f) {
     arr[0] = arr[1];
   } else {
     arr[0] = arr[2];
   }
   return arr[0];
 }
 
+class X {
+  var next;
+  X(this.next);
+}
+
+testPhiForwarding(obj) {
+  if (obj.next == null) {
+    return 1;
+  }
+
+  var len = 0;
+  while (obj != null) {
+    len++;
+    obj = obj.next;  // This load should not be forwarded.
+  }
+
+  return len;
+}
+
+testPhiForwarding2(obj) {
+  if (obj.next == null) {
+    return 1;
+  }
+
+  var len = 0, next = null;
+  while ((obj != null) && len < 2) {
+    len++;
+    obj = obj.next;  // This load should be forwarded.
+    next = obj.next;
+  }
+
+  return len;
+}
+
+class V {
+  final f;
+  V(this.f);
+}
+
+testPhiForwarding3() {
+  var a = new V(-0.1);
+  var c = new V(0.0);
+  var b = new V(0.1);
+
+  for (var i = 0; i < 3; i++) {
+    var af = a.f;
+    var bf = b.f;
+    var cf = c.f;
+    a = new V(cf);
+    b = new V(af);
+    c = new V(bf);
+  }
+
+  Expect.equals(-0.1, a.f);
+  Expect.equals(0.1, b.f);
+  Expect.equals(0.0, c.f);
+}
+
+testPhiForwarding4() {
+  var a = new V(-0.1);
+  var b = new V(0.1);
+  var c = new V(0.0);
+
+  var result = new List(9);
+  for (var i = 0, j = 0; i < 3; i++) {
+    result[j++] = a.f;
+    result[j++] = b.f;
+    result[j++] = c.f;
+    var xa = a;
+    var xb = b;
+    a = c;
+    b = xa;
+    c = xb;
+  }
+
+  Expect.listEquals([-0.1, 0.1, 0.0,
+                     0.0, -0.1, 0.1,
+                     0.1, 0.0, -0.1], result);
+}
+
+class U {
+  var x, y;
+  U() : x = 0, y = 0;
+}
+
+testEqualPhisElimination() {
+  var u = new U();
+  var v = new U();
+  var sum = 0;
+  for (var i = 0; i < 3; i++) {
+    u.x = i;
+    u.y = i;
+    if ((i & 1) == 1) {
+      v.x = i + 1;
+      v.y = i + 1;
+    } else {
+      v.x = i - 1;
+      v.y = i - 1;
+    }
+    sum += v.x + v.y;
+  }
+  Expect.equals(4, sum);
+  Expect.equals(2, u.x);
+  Expect.equals(2, u.y);
+}
+
 main() {
   final fixed = new List(10);
   final growable = [];
   testImmutableVMFields(fixed, true);
   testImmutableVMFields(growable, false);
   testImmutableVMFields(growable, false);
 
   final f64List = new Float64List(2);
   testPhiRepresentation(true, f64List);
   testPhiRepresentation(false, f64List);
 
+  final obj = new X(new X(new X(null)));
+
   for (var i = 0; i < 2000; i++) {
     Expect.listEquals([0x02010000, 0x03020100], foo(new A(0, 0)));
     Expect.listEquals([0x02010000, 0x03020100], bar(new A(0, 0), false));
     Expect.listEquals([0x04020000, 0x03020100], bar(new A(0, 0), true));
     testImmutableVMFields(fixed, true);
     testPhiRepresentation(true, f64List);
+    testPhiForwarding(obj);
+    testPhiForwarding2(obj);
+    testPhiForwarding3();
+    testPhiForwarding4();
+    testEqualPhisElimination();
   }
 
   Expect.equals(1, testImmutableVMFields([], false));
   Expect.equals(2, testImmutableVMFields([1], false));
   Expect.equals(2, testImmutableVMFields([1, 2], false));
   Expect.equals(3, testImmutableVMFields([1, 2, 3], false));
 
   final u32List = new Uint32List(3);
   u32List[0] = 0;
   u32List[1] = 0x3FFFFFFF;
   u32List[2] = 0x7FFFFFFF;
-  
+
   for (var i = 0; i < 4000; i++) {
     testPhiConvertions(true, u32List);
     testPhiConvertions(false, u32List);
   }
 }