First optimization in new compiler: simple GVN.
Change-Id: Ibe0efa4e84fd020a53ded310a92e0b4363f91b12
diff --git a/compiler/optimizing/gvn.h b/compiler/optimizing/gvn.h
new file mode 100644
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+++ b/compiler/optimizing/gvn.h
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+/*
+ * 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_GVN_H_
+#define ART_COMPILER_OPTIMIZING_GVN_H_
+
+#include <gtest/gtest.h>
+#include "nodes.h"
+
+namespace art {
+
+/**
+ * A node in the collision list of a ValueSet. Encodes the instruction,
+ * the hash code, and the next node in the collision list.
+ */
+class ValueSetNode : public ArenaObject {
+ public:
+ ValueSetNode(HInstruction* instruction, size_t hash_code, ValueSetNode* next)
+ : instruction_(instruction), hash_code_(hash_code), next_(next) {}
+
+ size_t GetHashCode() const { return hash_code_; }
+ HInstruction* GetInstruction() const { return instruction_; }
+ ValueSetNode* GetNext() const { return next_; }
+ void SetNext(ValueSetNode* node) { next_ = node; }
+
+ private:
+ HInstruction* const instruction_;
+ const size_t hash_code_;
+ ValueSetNode* next_;
+
+ DISALLOW_COPY_AND_ASSIGN(ValueSetNode);
+};
+
+/**
+ * A ValueSet holds instructions that can replace other instructions. It is updated
+ * through the `Add` method, and the `Kill` method. The `Kill` method removes
+ * instructions that are affected by the given side effect.
+ *
+ * The `Lookup` method returns an equivalent instruction to the given instruction
+ * if there is one in the set. In GVN, we would say those instructions have the
+ * same "number".
+ */
+class ValueSet : public ArenaObject {
+ public:
+ explicit ValueSet(ArenaAllocator* allocator)
+ : allocator_(allocator), number_of_entries_(0), collisions_(nullptr) {
+ for (size_t i = 0; i < kDefaultNumberOfEntries; ++i) {
+ table_[i] = nullptr;
+ }
+ }
+
+ // Adds an instruction in the set.
+ void Add(HInstruction* instruction) {
+ DCHECK(Lookup(instruction) == nullptr);
+ size_t hash_code = instruction->ComputeHashCode();
+ size_t index = hash_code % kDefaultNumberOfEntries;
+ if (table_[index] == nullptr) {
+ table_[index] = instruction;
+ } else {
+ collisions_ = new (allocator_) ValueSetNode(instruction, hash_code, collisions_);
+ }
+ ++number_of_entries_;
+ }
+
+ // If in the set, returns an equivalent instruction to the given instruction. Returns
+ // null otherwise.
+ HInstruction* Lookup(HInstruction* instruction) const {
+ size_t hash_code = instruction->ComputeHashCode();
+ size_t index = hash_code % kDefaultNumberOfEntries;
+ HInstruction* existing = table_[index];
+ if (existing != nullptr && existing->Equals(instruction)) {
+ return existing;
+ }
+
+ for (ValueSetNode* node = collisions_; node != nullptr; node = node->GetNext()) {
+ if (node->GetHashCode() == hash_code) {
+ existing = node->GetInstruction();
+ if (existing->Equals(instruction)) {
+ return existing;
+ }
+ }
+ }
+ return nullptr;
+ }
+
+ // Removes all instructions in the set that are affected by the given side effects.
+ void Kill(SideEffects side_effects) {
+ for (size_t i = 0; i < kDefaultNumberOfEntries; ++i) {
+ HInstruction* instruction = table_[i];
+ if (instruction != nullptr && instruction->GetSideEffects().DependsOn(side_effects)) {
+ table_[i] = nullptr;
+ --number_of_entries_;
+ }
+ }
+
+ ValueSetNode* current = collisions_;
+ ValueSetNode* previous = nullptr;
+ while (current != nullptr) {
+ HInstruction* instruction = current->GetInstruction();
+ if (instruction->GetSideEffects().DependsOn(side_effects)) {
+ if (previous == nullptr) {
+ collisions_ = current->GetNext();
+ } else {
+ previous->SetNext(current->GetNext());
+ }
+ --number_of_entries_;
+ } else {
+ previous = current;
+ }
+ current = current->GetNext();
+ }
+ }
+
+ // Returns a copy of this set.
+ ValueSet* Copy() const {
+ ValueSet* copy = new (allocator_) ValueSet(allocator_);
+
+ for (size_t i = 0; i < kDefaultNumberOfEntries; ++i) {
+ copy->table_[i] = table_[i];
+ }
+
+ // Note that the order will be inverted in the copy. This is fine, as the order is not
+ // relevant for a ValueSet.
+ for (ValueSetNode* node = collisions_; node != nullptr; node = node->GetNext()) {
+ copy->collisions_ = new (allocator_) ValueSetNode(
+ node->GetInstruction(), node->GetHashCode(), copy->collisions_);
+ }
+
+ copy->number_of_entries_ = number_of_entries_;
+ return copy;
+ }
+
+ bool IsEmpty() const { return number_of_entries_ == 0; }
+ size_t GetNumberOfEntries() const { return number_of_entries_; }
+
+ private:
+ static constexpr size_t kDefaultNumberOfEntries = 8;
+
+ ArenaAllocator* const allocator_;
+
+ // The number of entries in the set.
+ size_t number_of_entries_;
+
+ // The internal implementation of the set. It uses a combination of a hash code based
+ // fixed-size list, and a linked list to handle hash code collisions.
+ // TODO: Tune the fixed size list original size, and support growing it.
+ ValueSetNode* collisions_;
+ HInstruction* table_[kDefaultNumberOfEntries];
+
+ DISALLOW_COPY_AND_ASSIGN(ValueSet);
+};
+
+/**
+ * Optimization phase that removes redundant instruction.
+ */
+class GlobalValueNumberer : public ValueObject {
+ public:
+ GlobalValueNumberer(ArenaAllocator* allocator, HGraph* graph)
+ : allocator_(allocator),
+ graph_(graph),
+ block_effects_(allocator, graph->GetBlocks().Size()),
+ loop_effects_(allocator, graph->GetBlocks().Size()),
+ sets_(allocator, graph->GetBlocks().Size()),
+ visited_(allocator, graph->GetBlocks().Size()) {
+ size_t number_of_blocks = graph->GetBlocks().Size();
+ block_effects_.SetSize(number_of_blocks);
+ loop_effects_.SetSize(number_of_blocks);
+ sets_.SetSize(number_of_blocks);
+ visited_.SetSize(number_of_blocks);
+
+ for (size_t i = 0; i < number_of_blocks; ++i) {
+ block_effects_.Put(i, SideEffects::None());
+ loop_effects_.Put(i, SideEffects::None());
+ }
+ }
+
+ void Run();
+
+ private:
+ // Per-block GVN. Will also update the ValueSet of the dominated and
+ // successor blocks.
+ void VisitBasicBlock(HBasicBlock* block);
+
+ // Compute side effects of individual blocks and loops. The GVN algorithm
+ // will use these side effects to update the ValueSet of individual blocks.
+ void ComputeSideEffects();
+
+ void UpdateLoopEffects(HLoopInformation* info, SideEffects effects);
+ SideEffects GetLoopEffects(HBasicBlock* block) const;
+ SideEffects GetBlockEffects(HBasicBlock* block) const;
+
+ ArenaAllocator* const allocator_;
+ HGraph* const graph_;
+
+ // Side effects of individual blocks, that is the union of the side effects
+ // of the instructions in the block.
+ GrowableArray<SideEffects> block_effects_;
+
+ // Side effects of loops, that is the union of the side effects of the
+ // blocks contained in that loop.
+ GrowableArray<SideEffects> loop_effects_;
+
+ // ValueSet for blocks. Initially null, but for an individual block they
+ // are allocated and populated by the dominator, and updated by all blocks
+ // in the path from the dominator to the block.
+ GrowableArray<ValueSet*> sets_;
+
+ // Mark visisted blocks. Only used for debugging.
+ GrowableArray<bool> visited_;
+
+ FRIEND_TEST(GVNTest, LoopSideEffects);
+ DISALLOW_COPY_AND_ASSIGN(GlobalValueNumberer);
+};
+
+} // namespace art
+
+#endif // ART_COMPILER_OPTIMIZING_GVN_H_