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28 #ifndef V8_HYDROGEN_FLOW_ENGINE_H_
29 #define V8_HYDROGEN_FLOW_ENGINE_H_
32 #include "hydrogen-instructions.h"
38 // An example implementation of effects that doesn't collect anything.
39 class NoEffects : public ZoneObject {
41 explicit NoEffects(Zone* zone) { }
43 inline bool Disabled() {
44 return true; // Nothing to do.
46 template <class State>
47 inline void Apply(State* state) {
50 inline void Process(HInstruction* value, Zone* zone) {
53 inline void Union(NoEffects* other, Zone* zone) {
59 // An example implementation of state that doesn't track anything.
62 inline NoState* Copy(HBasicBlock* succ, Zone* zone) {
65 inline NoState* Process(HInstruction* value, Zone* zone) {
68 inline NoState* Merge(HBasicBlock* succ, NoState* other, Zone* zone) {
74 // This class implements an engine that can drive flow-sensitive analyses
75 // over a graph of basic blocks, either one block at a time (local analysis)
76 // or over the entire graph (global analysis). The flow engine is parameterized
77 // by the type of the state and the effects collected while walking over the
80 // The "State" collects which facts are known while passing over instructions
81 // in control flow order, and the "Effects" collect summary information about
82 // which facts could be invalidated on other control flow paths. The effects
83 // are necessary to correctly handle loops in the control flow graph without
84 // doing a fixed-point iteration. Thus the flow engine is guaranteed to visit
85 // each block at most twice; once for state, and optionally once for effects.
87 // The flow engine requires the State and Effects classes to implement methods
88 // like the example NoState and NoEffects above. It's not necessary to provide
89 // an effects implementation for local analysis.
90 template <class State, class Effects>
93 HFlowEngine(HGraph* graph, Zone* zone)
97 pred_counts_(graph->blocks()->length(), zone),
99 block_states_(graph->blocks()->length(), zone),
100 loop_effects_(graph->blocks()->length(), zone) {
101 loop_effects_.AddBlock(NULL, graph_->blocks()->length(), zone);
104 // Local analysis. Iterates over the instructions in the given block.
105 State* AnalyzeOneBlock(HBasicBlock* block, State* state) {
106 // Go through all instructions of the current block, updating the state.
107 for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
108 state = state->Process(it.Current(), zone_);
113 // Global analysis. Iterates over all blocks that are dominated by the given
114 // block, starting with the initial state. Computes effects for nested loops.
115 void AnalyzeDominatedBlocks(HBasicBlock* root, State* initial) {
117 SetStateAt(root, initial);
119 // Iterate all dominated blocks starting from the given start block.
120 for (int i = root->block_id(); i < graph_->blocks()->length(); i++) {
121 HBasicBlock* block = graph_->blocks()->at(i);
123 // Skip blocks not dominated by the root node.
124 if (SkipNonDominatedBlock(root, block)) continue;
125 State* state = StateAt(block);
127 if (block->IsReachable()) {
128 if (block->IsLoopHeader()) {
129 // Apply loop effects before analyzing loop body.
130 ComputeLoopEffects(block)->Apply(state);
132 // Must have visited all predecessors before this block.
133 CheckPredecessorCount(block);
136 // Go through all instructions of the current block, updating the state.
137 for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
138 state = state->Process(it.Current(), zone_);
142 // Propagate the block state forward to all successor blocks.
143 int max = block->end()->SuccessorCount();
144 for (int i = 0; i < max; i++) {
145 HBasicBlock* succ = block->end()->SuccessorAt(i);
146 IncrementPredecessorCount(succ);
147 if (StateAt(succ) == NULL) {
148 // This is the first state to reach the successor.
149 if (max == 1 && succ->predecessors()->length() == 1) {
150 // Optimization: successor can inherit this state.
151 SetStateAt(succ, state);
153 // Successor needs a copy of the state.
154 SetStateAt(succ, state->Copy(succ, block, zone_));
157 // Merge the current state with the state already at the successor.
158 SetStateAt(succ, StateAt(succ)->Merge(succ, state, block, zone_));
165 // Computes and caches the loop effects for the loop which has the given
166 // block as its loop header.
167 Effects* ComputeLoopEffects(HBasicBlock* block) {
168 ASSERT(block->IsLoopHeader());
169 Effects* effects = loop_effects_[block->block_id()];
170 if (effects != NULL) return effects; // Already analyzed this loop.
172 effects = new(zone_) Effects(zone_);
173 loop_effects_[block->block_id()] = effects;
174 if (effects->Disabled()) return effects; // No effects for this analysis.
176 HLoopInformation* loop = block->loop_information();
177 int end = loop->GetLastBackEdge()->block_id();
178 // Process the blocks between the header and the end.
179 for (int i = block->block_id(); i <= end; i++) {
180 HBasicBlock* member = graph_->blocks()->at(i);
181 if (i != block->block_id() && member->IsLoopHeader()) {
182 // Recursively compute and cache the effects of the nested loop.
183 ASSERT(member->loop_information()->parent_loop() == loop);
184 Effects* nested = ComputeLoopEffects(member);
185 effects->Union(nested, zone_);
186 // Skip the nested loop's blocks.
187 i = member->loop_information()->GetLastBackEdge()->block_id();
189 // Process all the effects of the block.
190 if (member->IsUnreachable()) continue;
191 ASSERT(member->current_loop() == loop);
192 for (HInstructionIterator it(member); !it.Done(); it.Advance()) {
193 effects->Process(it.Current(), zone_);
200 inline bool SkipNonDominatedBlock(HBasicBlock* root, HBasicBlock* other) {
201 if (root->block_id() == 0) return false; // Visit the whole graph.
202 if (root == other) return false; // Always visit the root.
203 return !root->Dominates(other); // Only visit dominated blocks.
206 inline State* StateAt(HBasicBlock* block) {
207 return block_states_.at(block->block_id());
210 inline void SetStateAt(HBasicBlock* block, State* state) {
211 block_states_.Set(block->block_id(), state);
214 inline void InitializeStates() {
216 pred_counts_.Rewind(0);
217 pred_counts_.AddBlock(0, graph_->blocks()->length(), zone_);
219 block_states_.Rewind(0);
220 block_states_.AddBlock(NULL, graph_->blocks()->length(), zone_);
223 inline void CheckPredecessorCount(HBasicBlock* block) {
224 ASSERT(block->predecessors()->length() == pred_counts_[block->block_id()]);
227 inline void IncrementPredecessorCount(HBasicBlock* block) {
229 pred_counts_[block->block_id()]++;
233 HGraph* graph_; // The hydrogen graph.
234 Zone* zone_; // Temporary zone.
236 ZoneList<int> pred_counts_; // Finished predecessors (by block id).
238 ZoneList<State*> block_states_; // Block states (by block id).
239 ZoneList<Effects*> loop_effects_; // Loop effects (by block id).
243 } } // namespace v8::internal
245 #endif // V8_HYDROGEN_FLOW_ENGINE_H_