Add two phi pruning phases.

Change-Id: Ic4f05e3df96970d78a6938b27cdf9b58ef3849b9

1 files changed, 68 insertions, 0 deletions

diff --git a/compiler/optimizing/ssa_phi_elimination.h b/compiler/optimizing/ssa_phi_elimination.h
new file mode 100644
index 0000000000..5274f09f3f
--- /dev/null
+++ b/compiler/optimizing/ssa_phi_elimination.h
@@ -0,0 +1,68 @@
+/*
+ * 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.
+ */
+
+#ifndef ART_COMPILER_OPTIMIZING_SSA_PHI_ELIMINATION_H_
+#define ART_COMPILER_OPTIMIZING_SSA_PHI_ELIMINATION_H_
+
+#include "nodes.h"
+
+namespace art {
+
+/**
+ * Optimization phase that removes dead phis from the graph. Dead phis are unused
+ * phis, or phis only used by other phis.
+ */
+class SsaDeadPhiElimination : public ValueObject {
+ public:
+  explicit SsaDeadPhiElimination(HGraph* graph)
+      : graph_(graph), worklist_(graph->GetArena(), kDefaultWorklistSize) {}
+
+  void Run();
+
+ private:
+  HGraph* const graph_;
+  GrowableArray<HPhi*> worklist_;
+
+  static constexpr size_t kDefaultWorklistSize = 8;
+
+  DISALLOW_COPY_AND_ASSIGN(SsaDeadPhiElimination);
+};
+
+/**
+ * Removes redundant phis that may have been introduced when doing SSA conversion.
+ * For example, when entering a loop, we create phis for all live registers. These
+ * registers might be updated with the same value, or not updated at all. We can just
+ * replace the phi with the value when entering the loop.
+ */
+class SsaRedundantPhiElimination : public ValueObject {
+ public:
+  explicit SsaRedundantPhiElimination(HGraph* graph)
+      : graph_(graph), worklist_(graph->GetArena(), kDefaultWorklistSize) {}
+
+  void Run();
+
+ private:
+  HGraph* const graph_;
+  GrowableArray<HPhi*> worklist_;
+
+  static constexpr size_t kDefaultWorklistSize = 8;
+
+  DISALLOW_COPY_AND_ASSIGN(SsaRedundantPhiElimination);
+};
+
+}  // namespace art
+
+#endif  // ART_COMPILER_OPTIMIZING_SSA_PHI_ELIMINATION_H_