Do not clobber dead temp registers at RestoreLiveRegisters as it may destroy the content of the res…

tests/language/issue21957_test.dart

Index: tests/language/issue21957_test.dart
===================================================================
--- tests/language/issue21957_test.dart	(revision 0)
+++ tests/language/issue21957_test.dart	(working copy)
@@ -0,0 +1,17 @@
+// 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.
+
+// Check slow path for PotentialUnboxedStore.
+// VMOptions=--optimization_counter_threshold=-1
+
+main() {
+  for (int i = 0; i < 1000000; i++) {
+    new A();
+  }
+}
+
+class A {
+  var a = 1.0;
+}
+