| // Copyright 2015 the V8 project authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef V8_COMPILER_DEAD_CODE_ELIMINATION_H_ |
| #define V8_COMPILER_DEAD_CODE_ELIMINATION_H_ |
| |
| #include "src/base/compiler-specific.h" |
| #include "src/compiler/graph-reducer.h" |
| #include "src/globals.h" |
| #include "src/machine-type.h" |
| |
| namespace v8 { |
| namespace internal { |
| namespace compiler { |
| |
| // Forward declarations. |
| class CommonOperatorBuilder; |
| |
| // Propagates {Dead} control and {DeadValue} values through the graph and |
| // thereby removes dead code. |
| // We detect dead values based on types, replacing uses of nodes with |
| // {Type::None()} with {DeadValue}. A pure node (other than a phi) using |
| // {DeadValue} is replaced by {DeadValue}. When {DeadValue} hits the effect |
| // chain, a crashing {Unreachable} node is inserted and the rest of the effect |
| // chain is collapsed. We wait for the {EffectControlLinearizer} to connect |
| // {Unreachable} nodes to the graph end, since this is much easier if there is |
| // no floating control. |
| // {DeadValue} has an input, which has to have {Type::None()}. This input is |
| // important to maintain the dependency on the cause of the unreachable code. |
| // {Unreachable} has a value output and {Type::None()} so it can be used by |
| // {DeadValue}. |
| // {DeadValue} nodes track a {MachineRepresentation} so they can be lowered to a |
| // value-producing node. {DeadValue} has the runtime semantics of crashing and |
| // behaves like a constant of its representation so it can be used in gap moves. |
| // Since phi nodes are the only remaining use of {DeadValue}, this |
| // representation is only adjusted for uses by phi nodes. |
| // In contrast to {DeadValue}, {Dead} can never remain in the graph. |
| class V8_EXPORT_PRIVATE DeadCodeElimination final |
| : public NON_EXPORTED_BASE(AdvancedReducer) { |
| public: |
| DeadCodeElimination(Editor* editor, Graph* graph, |
| CommonOperatorBuilder* common, Zone* temp_zone); |
| ~DeadCodeElimination() final {} |
| |
| const char* reducer_name() const override { return "DeadCodeElimination"; } |
| |
| Reduction Reduce(Node* node) final; |
| |
| private: |
| Reduction ReduceEnd(Node* node); |
| Reduction ReduceLoopOrMerge(Node* node); |
| Reduction ReduceLoopExit(Node* node); |
| Reduction ReduceNode(Node* node); |
| Reduction ReducePhi(Node* node); |
| Reduction ReducePureNode(Node* node); |
| Reduction ReduceUnreachableOrIfException(Node* node); |
| Reduction ReduceEffectNode(Node* node); |
| Reduction ReduceDeoptimizeOrReturnOrTerminate(Node* node); |
| Reduction ReduceBranchOrSwitch(Node* node); |
| |
| Reduction RemoveLoopExit(Node* node); |
| Reduction PropagateDeadControl(Node* node); |
| |
| void TrimMergeOrPhi(Node* node, int size); |
| |
| Node* DeadValue(Node* none_node, |
| MachineRepresentation rep = MachineRepresentation::kNone); |
| |
| Graph* graph() const { return graph_; } |
| CommonOperatorBuilder* common() const { return common_; } |
| Node* dead() const { return dead_; } |
| |
| Graph* const graph_; |
| CommonOperatorBuilder* const common_; |
| Node* const dead_; |
| Zone* zone_; |
| |
| DISALLOW_COPY_AND_ASSIGN(DeadCodeElimination); |
| }; |
| |
| } // namespace compiler |
| } // namespace internal |
| } // namespace v8 |
| |
| #endif // V8_COMPILER_DEAD_CODE_ELIMINATION_H_ |