optimizing: add block-scoped constructor fence merging pass
Introduce a new "Constructor Fence Redundancy Elimination" pass.
The pass currently performs local optimization only, i.e. within instructions
in the same basic block.
All constructor fences preceding a publish (e.g. store, invoke) get
merged into one instruction.
==============
OptStat#ConstructorFenceGeneratedNew: 43825
OptStat#ConstructorFenceGeneratedFinal: 17631 <+++
OptStat#ConstructorFenceRemovedLSE: 164
OptStat#ConstructorFenceRemovedPFRA: 9391
OptStat#ConstructorFenceRemovedCFRE: 16133 <---
Removes ~91.5% of the 'final' constructor fences in RitzBenchmark:
(We do not distinguish the exact reason that a fence was created, so
it's possible some "new" fences were also removed.)
==============
Test: art/test/run-test --host --optimizing 476-checker-ctor-fence-redun-elim
Bug: 36656456
Change-Id: I8020217b448ad96ce9b7640aa312ae784690ad99
diff --git a/compiler/optimizing/constructor_fence_redundancy_elimination.h b/compiler/optimizing/constructor_fence_redundancy_elimination.h
new file mode 100644
index 0000000..d89210c
--- /dev/null
+++ b/compiler/optimizing/constructor_fence_redundancy_elimination.h
@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2017 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_CONSTRUCTOR_FENCE_REDUNDANCY_ELIMINATION_H_
+#define ART_COMPILER_OPTIMIZING_CONSTRUCTOR_FENCE_REDUNDANCY_ELIMINATION_H_
+
+#include "optimization.h"
+
+namespace art {
+
+/*
+ * Constructor Fence Redundancy Elimination (CFRE).
+ *
+ * A local optimization pass that merges redundant constructor fences
+ * together within the same basic block.
+ *
+ * Abbreviations:
+ * - CF: Constructor Fence
+ * - CFS: Constructor Fence Set
+ * - CFTargets: The unique set of the inputs of all the instructions in CFS.
+ *
+ * Given any CFS = { CF(x), CF(y), CF(z), ... }, define CFTargets = { x, y, z, ... }.
+ * - Publish(R) must not exist for any R in CFTargets if this Publish(R) is between any CF in CFS.
+ * - This type of Publish(R) is called an "interesting publish".
+ *
+ * A Publish(R) is considered any instruction at which the reference to "R"
+ * may escape (e.g. invoke, store, return, etc) to another thread.
+ *
+ * Starting at the beginning of the block:
+ * - Find the largest contiguous CFS.
+ * - If we see an interesting publish, merge all instructions in CFS into a single CF(CFTargets).
+ * - Repeat until the block is fully visited.
+ * - At the end of the block, merge all instructions in CFS into a single CF(CFTargets).
+ */
+class ConstructorFenceRedundancyElimination : public HOptimization {
+ public:
+ ConstructorFenceRedundancyElimination(HGraph* graph,
+ OptimizingCompilerStats* stats)
+ : HOptimization(graph, kPassName, stats) {}
+
+ void Run() OVERRIDE;
+
+ static constexpr const char* kPassName = "constructor_fence_redundancy_elimination";
+
+ private:
+ DISALLOW_COPY_AND_ASSIGN(ConstructorFenceRedundancyElimination);
+};
+
+} // namespace art
+
+#endif // ART_COMPILER_OPTIMIZING_CONSTRUCTOR_FENCE_REDUNDANCY_ELIMINATION_H_