Fix variable allocator in the presence of HCheck instructions.

tests/language/issue9687_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.
+
+// Regression test for dart2js code generation in checked mode. See
+// last part of https://code.google.com/p/dart/issues/detail?id=9687.
+
+import "package:expect/expect.dart";
+
+class A {
+  final finalField;
+  final otherFinalField;
+
+  A() : finalField = 42, otherFinalField = 54;
+
+  expectFinalField(arg1, arg2) {
+    Expect.equals(arg1, arg2);
+    Expect.equals(finalField, arg1);
+  }
+
+  expectOtherFinalField(_, arg1, arg2) {
+    Expect.equals(arg1, arg2);
+    Expect.equals(otherFinalField, arg1);
+  }
+}
+
+var array = [new A()];
+
+main() {
+  // [untypedReceiver] is made so that the compiler does not know
+  // what it is.
+  var untypedReceiver = array[0];
+
+  // [typedReceiver] is made so that the compiler knows what it is.
+  var typedReceiver = new A();
+
+  // Using [: finalField :] twice will make the compiler want to
+  // allocate one temporary for it.
+  var a = untypedReceiver.expectFinalField(
+      typedReceiver.finalField, typedReceiver.finalField);
+
+  // Having a check instruction in between two allocations of
+  // temporary variables used to trigger a bug in the compiler.
+  int b = a;
+
+  // Using [: otherFinalField :] twice will make the compiler want to
+  // allocate one temporary for it. The compiler used to assign the
+  // same temporary for [: otherFinalField :] and [: finalField :].
+  untypedReceiver.expectOtherFinalField(
+      b, typedReceiver.otherFinalField, typedReceiver.otherFinalField);
+}