| // Copyright (c) 2016 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. |
| |
| #include "source/opt/unify_const_pass.h" |
| |
| #include <memory> |
| #include <unordered_map> |
| #include <utility> |
| #include <vector> |
| |
| #include "source/opt/def_use_manager.h" |
| #include "source/opt/ir_context.h" |
| #include "source/util/make_unique.h" |
| |
| namespace spvtools { |
| namespace opt { |
| namespace { |
| |
| // The trie that stores a bunch of result ids and, for a given instruction, |
| // searches the result id that has been defined with the same opcode, type and |
| // operands. |
| class ResultIdTrie { |
| public: |
| ResultIdTrie() : root_(new Node) {} |
| |
| // For a given instruction, extracts its opcode, type id and operand words |
| // as an array of keys, looks up the trie to find a result id which is stored |
| // with the same opcode, type id and operand words. If none of such result id |
| // is found, creates a trie node with those keys, stores the instruction's |
| // result id and returns that result id. If an existing result id is found, |
| // returns the existing result id. |
| uint32_t LookupEquivalentResultFor(const Instruction& inst) { |
| auto keys = GetLookUpKeys(inst); |
| auto* node = root_.get(); |
| for (uint32_t key : keys) { |
| node = node->GetOrCreateTrieNodeFor(key); |
| } |
| if (node->result_id() == 0) { |
| node->SetResultId(inst.result_id()); |
| } |
| return node->result_id(); |
| } |
| |
| private: |
| // The trie node to store result ids. |
| class Node { |
| public: |
| using TrieNodeMap = std::unordered_map<uint32_t, std::unique_ptr<Node>>; |
| |
| Node() : result_id_(0), next_() {} |
| uint32_t result_id() const { return result_id_; } |
| |
| // Sets the result id stored in this node. |
| void SetResultId(uint32_t id) { result_id_ = id; } |
| |
| // Searches for the child trie node with the given key. If the node is |
| // found, returns that node. Otherwise creates an empty child node with |
| // that key and returns that newly created node. |
| Node* GetOrCreateTrieNodeFor(uint32_t key) { |
| auto iter = next_.find(key); |
| if (iter == next_.end()) { |
| // insert a new node and return the node. |
| return next_.insert(std::make_pair(key, MakeUnique<Node>())) |
| .first->second.get(); |
| } |
| return iter->second.get(); |
| } |
| |
| private: |
| // The result id stored in this node. 0 means this node is empty. |
| uint32_t result_id_; |
| // The mapping from the keys to the child nodes of this node. |
| TrieNodeMap next_; |
| }; |
| |
| // Returns a vector of the opcode followed by the words in the raw SPIR-V |
| // instruction encoding but without the result id. |
| std::vector<uint32_t> GetLookUpKeys(const Instruction& inst) { |
| std::vector<uint32_t> keys; |
| // Need to use the opcode, otherwise there might be a conflict with the |
| // following case when <op>'s binary value equals xx's id: |
| // OpSpecConstantOp tt <op> yy zz |
| // OpSpecConstantComposite tt xx yy zz; |
| keys.push_back(static_cast<uint32_t>(inst.opcode())); |
| for (const auto& operand : inst) { |
| if (operand.type == SPV_OPERAND_TYPE_RESULT_ID) continue; |
| keys.insert(keys.end(), operand.words.cbegin(), operand.words.cend()); |
| } |
| return keys; |
| } |
| |
| std::unique_ptr<Node> root_; // The root node of the trie. |
| }; |
| } // namespace |
| |
| Pass::Status UnifyConstantPass::Process() { |
| bool modified = false; |
| ResultIdTrie defined_constants; |
| |
| for (Instruction *next_instruction, |
| *inst = &*(context()->types_values_begin()); |
| inst; inst = next_instruction) { |
| next_instruction = inst->NextNode(); |
| |
| // Do not handle the instruction when there are decorations upon the result |
| // id. |
| if (get_def_use_mgr()->GetAnnotations(inst->result_id()).size() != 0) { |
| continue; |
| } |
| |
| // The overall algorithm is to store the result ids of all the eligible |
| // constants encountered so far in a trie. For a constant defining |
| // instruction under consideration, use its opcode, result type id and |
| // words in operands as an array of keys to lookup the trie. If a result id |
| // can be found for that array of keys, a constant with exactly the same |
| // value must has been defined before, the constant under processing |
| // should be replaced by the constant previously defined. If no such result |
| // id can be found for that array of keys, this must be the first time a |
| // constant with its value be defined, we then create a new trie node to |
| // store the result id with the keys. When replacing a duplicated constant |
| // with a previously defined constant, all the uses of the duplicated |
| // constant, which must be placed after the duplicated constant defining |
| // instruction, will be updated. This way, the descendants of the |
| // previously defined constant and the duplicated constant will both refer |
| // to the previously defined constant. So that the operand ids which are |
| // used in key arrays will be the ids of the unified constants, when |
| // processing is up to a descendant. This makes comparing the key array |
| // always valid for judging duplication. |
| switch (inst->opcode()) { |
| case spv::Op::OpConstantTrue: |
| case spv::Op::OpConstantFalse: |
| case spv::Op::OpConstant: |
| case spv::Op::OpConstantNull: |
| case spv::Op::OpConstantSampler: |
| case spv::Op::OpConstantComposite: |
| // Only spec constants defined with OpSpecConstantOp and |
| // OpSpecConstantComposite should be processed in this pass. Spec |
| // constants defined with OpSpecConstant{|True|False} are decorated with |
| // 'SpecId' decoration and all of them should be treated as unique. |
| // 'SpecId' is not applicable to SpecConstants defined with |
| // OpSpecConstant{Op|Composite}, their values are not necessary to be |
| // unique. When all the operands/components are the same between two |
| // OpSpecConstant{Op|Composite} results, their result values must be the |
| // same so are unifiable. |
| case spv::Op::OpSpecConstantOp: |
| case spv::Op::OpSpecConstantComposite: { |
| uint32_t id = defined_constants.LookupEquivalentResultFor(*inst); |
| if (id != inst->result_id()) { |
| // The constant is a duplicated one, use the cached constant to |
| // replace the uses of this duplicated one, then turn it to nop. |
| context()->ReplaceAllUsesWith(inst->result_id(), id); |
| context()->KillInst(inst); |
| modified = true; |
| } |
| break; |
| } |
| default: |
| break; |
| } |
| } |
| return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange; |
| } |
| |
| } // namespace opt |
| } // namespace spvtools |