Don't assign safepoint at the definition to the definition's live-range.

tests/standalone/slowpath_safepoints_test.dart

+// Copyright (c) 2014, 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 that safepoints associated with slowpaths don't mark non-existing values
+// alive.
+// VMOptions=--optimization-counter-threshold=5 --no-inline_alloc --gc_at_instance_allocation=_Double
+
+class C {
+  final next;
+  C(this.next);
+}
+
+
+noop(a1, a2, a3, a4, a5, a6, a7, a8, a9) => 0;
+
+crash(f, i) {
+  final obj1 = new C(null);
+  final obj2 = new C(obj1);
+  final obj3 = new C(obj2);
+  final obj4 = new C(obj3);
+  final obj5 = new C(obj4);
+  final obj6 = new C(obj5);
+  final obj7 = new C(obj6);
+  final obj8 = new C(obj7);
+  final obj9 = new C(obj8);
+
+  f(obj1, obj2, obj3, obj4, obj5, obj6, obj7, obj8, obj9);
+  f(obj1, obj2, obj3, obj4, obj5, obj6, obj7, obj8, obj9);
+
+  final d1 = (i + 0).toDouble();
+  final d2 = (i + 1).toDouble();
+  final d3 = (i + 2).toDouble();
+  final d4 = (i + 3).toDouble();
+  final d5 = (i + 4).toDouble();
+  final d6 = (i + 5).toDouble();
+  final d7 = (i + 6).toDouble();
+  final d8 = (i + 7).toDouble();
+  final d9 = (i + 8).toDouble();
+
+  f(d1, d2, d3, d4, d5, d6, d7, d8, d9);
+  f(d1, d2, d3, d4, d5, d6, d7, d8, d9);
+}
+
+main() {
+  for (var i = 0; i < 10; i++) {
+    print(i);
+    crash(noop, 10);
+  }
+}