1 // Copyright (c) 2016 Google Inc. 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 #include "source/opt/unify_const_pass.h" 16 17 #include <memory> 18 #include <unordered_map> 19 #include <utility> 20 #include <vector> 21 22 #include "source/opt/def_use_manager.h" 23 #include "source/opt/ir_context.h" 24 #include "source/util/make_unique.h" 25 26 namespace spvtools { 27 namespace opt { 28 29 namespace { 30 31 // The trie that stores a bunch of result ids and, for a given instruction, 32 // searches the result id that has been defined with the same opcode, type and 33 // operands. 34 class ResultIdTrie { 35 public: 36 ResultIdTrie() : root_(new Node) {} 37 38 // For a given instruction, extracts its opcode, type id and operand words 39 // as an array of keys, looks up the trie to find a result id which is stored 40 // with the same opcode, type id and operand words. If none of such result id 41 // is found, creates a trie node with those keys, stores the instruction's 42 // result id and returns that result id. If an existing result id is found, 43 // returns the existing result id. 44 uint32_t LookupEquivalentResultFor(const Instruction& inst) { 45 auto keys = GetLookUpKeys(inst); 46 auto* node = root_.get(); 47 for (uint32_t key : keys) { 48 node = node->GetOrCreateTrieNodeFor(key); 49 } 50 if (node->result_id() == 0) { 51 node->SetResultId(inst.result_id()); 52 } 53 return node->result_id(); 54 } 55 56 private: 57 // The trie node to store result ids. 58 class Node { 59 public: 60 using TrieNodeMap = std::unordered_map<uint32_t, std::unique_ptr<Node>>; 61 62 Node() : result_id_(0), next_() {} 63 uint32_t result_id() const { return result_id_; } 64 65 // Sets the result id stored in this node. 66 void SetResultId(uint32_t id) { result_id_ = id; } 67 68 // Searches for the child trie node with the given key. If the node is 69 // found, returns that node. Otherwise creates an empty child node with 70 // that key and returns that newly created node. 71 Node* GetOrCreateTrieNodeFor(uint32_t key) { 72 auto iter = next_.find(key); 73 if (iter == next_.end()) { 74 // insert a new node and return the node. 75 return next_.insert(std::make_pair(key, MakeUnique<Node>())) 76 .first->second.get(); 77 } 78 return iter->second.get(); 79 } 80 81 private: 82 // The result id stored in this node. 0 means this node is empty. 83 uint32_t result_id_; 84 // The mapping from the keys to the child nodes of this node. 85 TrieNodeMap next_; 86 }; 87 88 // Returns a vector of the opcode followed by the words in the raw SPIR-V 89 // instruction encoding but without the result id. 90 std::vector<uint32_t> GetLookUpKeys(const Instruction& inst) { 91 std::vector<uint32_t> keys; 92 // Need to use the opcode, otherwise there might be a conflict with the 93 // following case when <op>'s binary value equals xx's id: 94 // OpSpecConstantOp tt <op> yy zz 95 // OpSpecConstantComposite tt xx yy zz; 96 keys.push_back(static_cast<uint32_t>(inst.opcode())); 97 for (const auto& operand : inst) { 98 if (operand.type == SPV_OPERAND_TYPE_RESULT_ID) continue; 99 keys.insert(keys.end(), operand.words.cbegin(), operand.words.cend()); 100 } 101 return keys; 102 } 103 104 std::unique_ptr<Node> root_; // The root node of the trie. 105 }; 106 } // anonymous namespace 107 108 Pass::Status UnifyConstantPass::Process() { 109 bool modified = false; 110 ResultIdTrie defined_constants; 111 112 for (Instruction *next_instruction, 113 *inst = &*(context()->types_values_begin()); 114 inst; inst = next_instruction) { 115 next_instruction = inst->NextNode(); 116 117 // Do not handle the instruction when there are decorations upon the result 118 // id. 119 if (get_def_use_mgr()->GetAnnotations(inst->result_id()).size() != 0) { 120 continue; 121 } 122 123 // The overall algorithm is to store the result ids of all the eligible 124 // constants encountered so far in a trie. For a constant defining 125 // instruction under consideration, use its opcode, result type id and 126 // words in operands as an array of keys to lookup the trie. If a result id 127 // can be found for that array of keys, a constant with exactly the same 128 // value must has been defined before, the constant under processing 129 // should be replaced by the constant previously defined. If no such result 130 // id can be found for that array of keys, this must be the first time a 131 // constant with its value be defined, we then create a new trie node to 132 // store the result id with the keys. When replacing a duplicated constant 133 // with a previously defined constant, all the uses of the duplicated 134 // constant, which must be placed after the duplicated constant defining 135 // instruction, will be updated. This way, the descendants of the 136 // previously defined constant and the duplicated constant will both refer 137 // to the previously defined constant. So that the operand ids which are 138 // used in key arrays will be the ids of the unified constants, when 139 // processing is up to a descendant. This makes comparing the key array 140 // always valid for judging duplication. 141 switch (inst->opcode()) { 142 case SpvOp::SpvOpConstantTrue: 143 case SpvOp::SpvOpConstantFalse: 144 case SpvOp::SpvOpConstant: 145 case SpvOp::SpvOpConstantNull: 146 case SpvOp::SpvOpConstantSampler: 147 case SpvOp::SpvOpConstantComposite: 148 // Only spec constants defined with OpSpecConstantOp and 149 // OpSpecConstantComposite should be processed in this pass. Spec 150 // constants defined with OpSpecConstant{|True|False} are decorated with 151 // 'SpecId' decoration and all of them should be treated as unique. 152 // 'SpecId' is not applicable to SpecConstants defined with 153 // OpSpecConstant{Op|Composite}, their values are not necessary to be 154 // unique. When all the operands/compoents are the same between two 155 // OpSpecConstant{Op|Composite} results, their result values must be the 156 // same so are unifiable. 157 case SpvOp::SpvOpSpecConstantOp: 158 case SpvOp::SpvOpSpecConstantComposite: { 159 uint32_t id = defined_constants.LookupEquivalentResultFor(*inst); 160 if (id != inst->result_id()) { 161 // The constant is a duplicated one, use the cached constant to 162 // replace the uses of this duplicated one, then turn it to nop. 163 context()->ReplaceAllUsesWith(inst->result_id(), id); 164 context()->KillInst(inst); 165 modified = true; 166 } 167 break; 168 } 169 default: 170 break; 171 } 172 } 173 return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange; 174 } 175 176 } // namespace opt 177 } // namespace spvtools 178