// Copyright (c) 2017 Google Inc. // // 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 SOURCE_OPT_VALUE_NUMBER_TABLE_H_ #define SOURCE_OPT_VALUE_NUMBER_TABLE_H_ #include <cstdint> #include <unordered_map> #include "source/opt/instruction.h" namespace spvtools { namespace opt { class IRContext; // Returns true if the two instructions compute the same value. Used by the // value number table to compare two instructions. class ComputeSameValue { public: bool operator()(const Instruction& lhs, const Instruction& rhs) const; }; // The hash function used in the value number table. class ValueTableHash { public: std::size_t operator()(const Instruction& inst) const; }; // This class implements the value number analysis. It is using a hash-based // approach to value numbering. It is essentially doing dominator-tree value // numbering described in // // Preston Briggs, Keith D. Cooper, and L. Taylor Simpson. 1997. Value // numbering. Softw. Pract. Exper. 27, 6 (June 1997), 701-724. // https://www.cs.rice.edu/~keith/Promo/CRPC-TR94517.pdf.gz // // The main difference is that because we do not perform redundancy elimination // as we build the value number table, we do not have to deal with cleaning up // the scope. class ValueNumberTable { public: ValueNumberTable(IRContext* ctx) : context_(ctx), next_value_number_(1) { BuildDominatorTreeValueNumberTable(); } // Returns the value number of the value computed by |inst|. |inst| must have // a result id that will hold the computed value. If no value number has been // assigned to the result id, then the return value is 0. uint32_t GetValueNumber(Instruction* inst) const; // Returns the value number of the value contain in |id|. Returns 0 if it // has not been assigned a value number. uint32_t GetValueNumber(uint32_t id) const; IRContext* context() const { return context_; } private: // Assigns a value number to every result id in the module. void BuildDominatorTreeValueNumberTable(); // Returns the new value number. uint32_t TakeNextValueNumber() { return next_value_number_++; } // Assigns a new value number to the result of |inst| if it does not already // have one. Return the value number for |inst|. |inst| must have a result // id. uint32_t AssignValueNumber(Instruction* inst); std::unordered_map<Instruction, uint32_t, ValueTableHash, ComputeSameValue> instruction_to_value_; std::unordered_map<uint32_t, uint32_t> id_to_value_; IRContext* context_; uint32_t next_value_number_; }; } // namespace opt } // namespace spvtools #endif // SOURCE_OPT_VALUE_NUMBER_TABLE_H_