Initiate a dead code elimination pass in the optimizing compiler.

Change-Id: Ie9db5d8e2c2c30e34145a0f7d2386b8ec58cfc4e

1 files changed, 45 insertions, 0 deletions

diff --git a/compiler/optimizing/dead_code_elimination.cc b/compiler/optimizing/dead_code_elimination.cc
new file mode 100644
index 0000000000..2f881d1b6d
--- /dev/null
+++ b/compiler/optimizing/dead_code_elimination.cc
@@ -0,0 +1,45 @@
+/*
+ * 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 "dead_code_elimination.h"
+
+#include "base/bit_vector-inl.h"
+
+namespace art {
+
+void DeadCodeElimination::Run() {
+  // Process basic blocks in post-order in the dominator tree, so that
+  // a dead instruction depending on another dead instruction is
+  // removed.
+  for (HPostOrderIterator b(*graph_); !b.Done(); b.Advance()) {
+    HBasicBlock* block = b.Current();
+    // Traverse this block's instructions in backward order and remove
+    // the unused ones.
+    HBackwardInstructionIterator i(block->GetInstructions());
+    // Skip the first iteration, as the last instruction of a block is
+    // a branching instruction.
+    DCHECK(i.Current()->IsControlFlow());
+    for (i.Advance(); !i.Done(); i.Advance()) {
+      HInstruction* inst = i.Current();
+      DCHECK(!inst->IsControlFlow());
+      if (!inst->HasSideEffects() && !inst->HasUses()) {
+        block->RemoveInstruction(inst);
+      }
+    }
+  }
+}
+
+}  // namespace art