1 // Copyright (c) 2018 Google LLC 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #ifndef SOURCE_OPT_CONST_FOLDING_RULES_H_ 16 #define SOURCE_OPT_CONST_FOLDING_RULES_H_ 17 18 #include <unordered_map> 19 #include <vector> 20 21 #include "source/opt/constants.h" 22 23 namespace spvtools { 24 namespace opt { 25 26 // Constant Folding Rules: 27 // 28 // The folding mechanism is built around the concept of a |ConstantFoldingRule|. 29 // A constant folding rule is a function that implements a method of simplifying 30 // an instruction to a constant. 31 // 32 // The inputs to a folding rule are: 33 // |inst| - the instruction to be simplified. 34 // |constants| - if an in-operands is an id of a constant, then the 35 // corresponding value in |constants| contains that 36 // constant value. Otherwise, the corresponding entry in 37 // |constants| is |nullptr|. 38 // 39 // A constant folding rule returns a pointer to an Constant if |inst| can be 40 // simplified using this rule. Otherwise, it returns |nullptr|. 41 // 42 // See const_folding_rules.cpp for examples on how to write a constant folding 43 // rule. 44 // 45 // Be sure to add new constant folding rules to the table of constant folding 46 // rules in the constructor for ConstantFoldingRules. The new rule should be 47 // added to the list for every opcode that it applies to. Note that earlier 48 // rules in the list are given priority. That is, if an earlier rule is able to 49 // fold an instruction, the later rules will not be attempted. 50 51 using ConstantFoldingRule = std::function<const analysis::Constant*( 52 IRContext* ctx, Instruction* inst, 53 const std::vector<const analysis::Constant*>& constants)>; 54 55 class ConstantFoldingRules { 56 protected: 57 // The |Key| and |Value| structs are used to by-pass a "decorated name length 58 // exceeded, name was truncated" warning on VS2013 and VS2015. 59 struct Key { 60 uint32_t instruction_set; 61 uint32_t opcode; 62 }; 63 64 friend bool operator<(const Key& a, const Key& b) { 65 if (a.instruction_set < b.instruction_set) { 66 return true; 67 } 68 if (a.instruction_set > b.instruction_set) { 69 return false; 70 } 71 return a.opcode < b.opcode; 72 } 73 74 struct Value { 75 std::vector<ConstantFoldingRule> value; push_backValue76 void push_back(ConstantFoldingRule rule) { value.push_back(rule); } 77 }; 78 79 public: ConstantFoldingRules(IRContext * ctx)80 ConstantFoldingRules(IRContext* ctx) : context_(ctx) {} 81 virtual ~ConstantFoldingRules() = default; 82 83 // Returns true if there is at least 1 folding rule for |opcode|. HasFoldingRule(const Instruction * inst)84 bool HasFoldingRule(const Instruction* inst) const { 85 return !GetRulesForInstruction(inst).empty(); 86 } 87 88 // Returns true if there is at least 1 folding rule for |inst|. GetRulesForInstruction(const Instruction * inst)89 const std::vector<ConstantFoldingRule>& GetRulesForInstruction( 90 const Instruction* inst) const { 91 if (inst->opcode() != SpvOpExtInst) { 92 auto it = rules_.find(inst->opcode()); 93 if (it != rules_.end()) { 94 return it->second.value; 95 } 96 } else { 97 uint32_t ext_inst_id = inst->GetSingleWordInOperand(0); 98 uint32_t ext_opcode = inst->GetSingleWordInOperand(1); 99 auto it = ext_rules_.find({ext_inst_id, ext_opcode}); 100 if (it != ext_rules_.end()) { 101 return it->second.value; 102 } 103 } 104 return empty_vector_; 105 } 106 107 // Add the folding rules. 108 virtual void AddFoldingRules(); 109 110 protected: 111 // |rules[opcode]| is the set of rules that can be applied to instructions 112 // with |opcode| as the opcode. 113 std::unordered_map<uint32_t, Value> rules_; 114 115 // The folding rules for extended instructions. 116 std::map<Key, Value> ext_rules_; 117 118 private: 119 // The context that the instruction to be folded will be a part of. 120 IRContext* context_; 121 122 // The empty set of rules to be used as the default return value in 123 // |GetRulesForInstruction|. 124 std::vector<ConstantFoldingRule> empty_vector_; 125 }; 126 127 } // namespace opt 128 } // namespace spvtools 129 130 #endif // SOURCE_OPT_CONST_FOLDING_RULES_H_ 131