Introduce a class to implement optimization passes.

- Add art::HOptimization.
- Rename art::ConstantPropagation to art::HConstantFolding in
  compiler/optimizing/constant_folding.h to avoid name
  clashes with a class of the same name in
  compiler/dex/post_opt_passes.h.
- Rename art::DeadCodeElimination to
  art::HDeadCodeElimination for consistency reasons.
- Have art::HDeadCodeElimination and art::HConstantFolding
  derive from art::HOptimization.
- Start to use these optimizations in
  art:OptimizingCompiler::TryCompile.

Change-Id: Iaab350c122d87b2333b3760312b15c0592d7e010

1 files changed, 47 insertions, 0 deletions

diff --git a/compiler/optimizing/constant_folding.cc b/compiler/optimizing/constant_folding.cc
new file mode 100644
index 0000000000..0b3ad9809f
--- /dev/null
+++ b/compiler/optimizing/constant_folding.cc
@@ -0,0 +1,47 @@
+/*
+ * 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 "constant_folding.h"
+
+namespace art {
+
+void HConstantFolding::Run() {
+  // Process basic blocks in reverse post-order in the dominator tree,
+  // so that an instruction turned into a constant, used as input of
+  // another instruction, may possibly be used to turn that second
+  // instruction into a constant as well.
+  for (HReversePostOrderIterator it(*graph_); !it.Done(); it.Advance()) {
+    HBasicBlock* block = it.Current();
+    // Traverse this block's instructions in (forward) order and
+    // replace the ones that can be statically evaluated by a
+    // compile-time counterpart.
+    for (HInstructionIterator it(block->GetInstructions());
+         !it.Done(); it.Advance()) {
+      HInstruction* inst = it.Current();
+      // Constant folding: replace `c <- a op b' with a compile-time
+      // evaluation of `a op b' if `a' and `b' are constant.
+      if (inst->IsBinaryOperation()) {
+        HConstant* constant =
+          inst->AsBinaryOperation()->TryStaticEvaluation(graph_->GetArena());
+        if (constant != nullptr) {
+          inst->GetBlock()->ReplaceAndRemoveInstructionWith(inst, constant);
+        }
+      }
+    }
+  }
+}
+
+}  // namespace art