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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->IsLoopHeader()) {
128 // Apply loop effects before analyzing loop body.
129 ComputeLoopEffects(block)->Apply(state);
131 // Must have visited all predecessors before this block.
132 CheckPredecessorCount(block);
135 // Go through all instructions of the current block, updating the state.
136 for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
137 state = state->Process(it.Current(), zone_);
140 // Propagate the block state forward to all successor blocks.
141 int max = block->end()->SuccessorCount();
142 for (int i = 0; i < max; i++) {
143 HBasicBlock* succ = block->end()->SuccessorAt(i);
144 IncrementPredecessorCount(succ);
145 if (StateAt(succ) == NULL) {
146 // This is the first state to reach the successor.
147 if (max == 1 && succ->predecessors()->length() == 1) {
148 // Optimization: successor can inherit this state.
149 SetStateAt(succ, state);
151 // Successor needs a copy of the state.
152 SetStateAt(succ, state->Copy(succ, zone_));
155 // Merge the current state with the state already at the successor.
156 SetStateAt(succ, state->Merge(succ, StateAt(succ), zone_));
163 // Computes and caches the loop effects for the loop which has the given
164 // block as its loop header.
165 Effects* ComputeLoopEffects(HBasicBlock* block) {
166 ASSERT(block->IsLoopHeader());
167 Effects* effects = loop_effects_[block->block_id()];
168 if (effects != NULL) return effects; // Already analyzed this loop.
170 effects = new(zone_) Effects(zone_);
171 loop_effects_[block->block_id()] = effects;
172 if (effects->Disabled()) return effects; // No effects for this analysis.
174 HLoopInformation* loop = block->loop_information();
175 int end = loop->GetLastBackEdge()->block_id();
176 // Process the blocks between the header and the end.
177 for (int i = block->block_id(); i <= end; i++) {
178 HBasicBlock* member = graph_->blocks()->at(i);
179 if (i != block->block_id() && member->IsLoopHeader()) {
180 // Recursively compute and cache the effects of the nested loop.
181 ASSERT(member->loop_information()->parent_loop() == loop);
182 Effects* nested = ComputeLoopEffects(member);
183 effects->Union(nested, zone_);
184 // Skip the nested loop's blocks.
185 i = member->loop_information()->GetLastBackEdge()->block_id();
187 // Process all the effects of the block.
188 ASSERT(member->current_loop() == loop);
189 for (HInstructionIterator it(member); !it.Done(); it.Advance()) {
190 effects->Process(it.Current(), zone_);
197 inline bool SkipNonDominatedBlock(HBasicBlock* root, HBasicBlock* other) {
198 if (root->block_id() == 0) return false; // Visit the whole graph.
199 if (root == other) return false; // Always visit the root.
200 return !root->Dominates(other); // Only visit dominated blocks.
203 inline State* StateAt(HBasicBlock* block) {
204 return block_states_.at(block->block_id());
207 inline void SetStateAt(HBasicBlock* block, State* state) {
208 block_states_.Set(block->block_id(), state);
211 inline void InitializeStates() {
213 pred_counts_.Rewind(0);
214 pred_counts_.AddBlock(0, graph_->blocks()->length(), zone_);
216 block_states_.Rewind(0);
217 block_states_.AddBlock(NULL, graph_->blocks()->length(), zone_);
220 inline void CheckPredecessorCount(HBasicBlock* block) {
221 ASSERT(block->predecessors()->length() == pred_counts_[block->block_id()]);
224 inline void IncrementPredecessorCount(HBasicBlock* block) {
226 pred_counts_[block->block_id()]++;
230 HGraph* graph_; // The hydrogen graph.
231 Zone* zone_; // Temporary zone.
233 ZoneList<int> pred_counts_; // Finished predecessors (by block id).
235 ZoneList<State*> block_states_; // Block states (by block id).
236 ZoneList<Effects*> loop_effects_; // Loop effects (by block id).
240 } } // namespace v8::internal
242 #endif // V8_HYDROGEN_FLOW_ENGINE_H_