Add a prepare for register allocation pass.

- Currently the pass just changes the uses of checks to the
  actual values.
- Also optimize array access, now that inputs can be constants.
- And fix another bug in the register allocator reveiled by
  this change.

Change-Id: I43be0dbde9330ee5c8f9d678de11361292d8bd98
diff --git a/compiler/optimizing/prepare_for_register_allocation.cc b/compiler/optimizing/prepare_for_register_allocation.cc
new file mode 100644
index 0000000..bfbbab5
--- /dev/null
+++ b/compiler/optimizing/prepare_for_register_allocation.cc
@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2014 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.
+ */
+
+#include "prepare_for_register_allocation.h"
+
+namespace art {
+
+void PrepareForRegisterAllocation::Run() {
+  // Order does not matter.
+  for (HReversePostOrderIterator it(*GetGraph()); !it.Done(); it.Advance()) {
+    HBasicBlock* block = it.Current();
+    // No need to visit the phis.
+    for (HInstructionIterator it(block->GetInstructions()); !it.Done(); it.Advance()) {
+      it.Current()->Accept(this);
+    }
+  }
+}
+
+void PrepareForRegisterAllocation::VisitNullCheck(HNullCheck* check) {
+  check->ReplaceWith(check->InputAt(0));
+}
+
+void PrepareForRegisterAllocation::VisitBoundsCheck(HBoundsCheck* check) {
+  check->ReplaceWith(check->InputAt(0));
+}
+
+}  // namespace art