Use dominance information for null optimization in write barrier.

Change-Id: I8b57dafcd321c9afa1bbfc6a0674cbea15cbf10c
diff --git a/test/532-checker-nonnull-arrayset/src/Main.java b/test/532-checker-nonnull-arrayset/src/Main.java
new file mode 100644
index 0000000..7d8fff4
--- /dev/null
+++ b/test/532-checker-nonnull-arrayset/src/Main.java
@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+public class Main {
+
+  // Check that we don't put a null check in the card marking code.
+
+  /// CHECK-START: void Main.test() instruction_simplifier (before)
+  /// CHECK:          ArraySet value_can_be_null:true
+
+  /// CHECK-START: void Main.test() instruction_simplifier (after)
+  /// CHECK:          ArraySet value_can_be_null:false
+
+  /// CHECK-START-X86: void Main.test() disassembly (after)
+  /// CHECK:          ArraySet value_can_be_null:false
+  /// CHECK-NOT:      test
+  /// CHECK:          ReturnVoid
+  public static void test() {
+    Object[] array = new Object[1];
+    Object nonNull = array[0];
+    nonNull.getClass(); // Ensure nonNull has an implicit null check.
+    array[0] = nonNull;
+  }
+
+  public static void main(String[] args) {}
+}