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178 lines
6.9 KiB
178 lines
6.9 KiB
// Copyright (c) 2016 Google Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "source/opt/unify_const_pass.h"
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#include <memory>
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#include <unordered_map>
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#include <utility>
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#include <vector>
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#include "source/opt/def_use_manager.h"
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#include "source/opt/ir_context.h"
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#include "source/util/make_unique.h"
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namespace spvtools {
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namespace opt {
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namespace {
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// The trie that stores a bunch of result ids and, for a given instruction,
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// searches the result id that has been defined with the same opcode, type and
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// operands.
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class ResultIdTrie {
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public:
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ResultIdTrie() : root_(new Node) {}
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// For a given instruction, extracts its opcode, type id and operand words
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// as an array of keys, looks up the trie to find a result id which is stored
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// with the same opcode, type id and operand words. If none of such result id
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// is found, creates a trie node with those keys, stores the instruction's
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// result id and returns that result id. If an existing result id is found,
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// returns the existing result id.
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uint32_t LookupEquivalentResultFor(const Instruction& inst) {
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auto keys = GetLookUpKeys(inst);
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auto* node = root_.get();
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for (uint32_t key : keys) {
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node = node->GetOrCreateTrieNodeFor(key);
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}
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if (node->result_id() == 0) {
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node->SetResultId(inst.result_id());
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}
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return node->result_id();
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}
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private:
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// The trie node to store result ids.
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class Node {
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public:
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using TrieNodeMap = std::unordered_map<uint32_t, std::unique_ptr<Node>>;
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Node() : result_id_(0), next_() {}
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uint32_t result_id() const { return result_id_; }
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// Sets the result id stored in this node.
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void SetResultId(uint32_t id) { result_id_ = id; }
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// Searches for the child trie node with the given key. If the node is
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// found, returns that node. Otherwise creates an empty child node with
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// that key and returns that newly created node.
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Node* GetOrCreateTrieNodeFor(uint32_t key) {
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auto iter = next_.find(key);
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if (iter == next_.end()) {
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// insert a new node and return the node.
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return next_.insert(std::make_pair(key, MakeUnique<Node>()))
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.first->second.get();
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}
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return iter->second.get();
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}
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private:
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// The result id stored in this node. 0 means this node is empty.
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uint32_t result_id_;
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// The mapping from the keys to the child nodes of this node.
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TrieNodeMap next_;
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};
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// Returns a vector of the opcode followed by the words in the raw SPIR-V
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// instruction encoding but without the result id.
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std::vector<uint32_t> GetLookUpKeys(const Instruction& inst) {
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std::vector<uint32_t> keys;
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// Need to use the opcode, otherwise there might be a conflict with the
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// following case when <op>'s binary value equals xx's id:
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// OpSpecConstantOp tt <op> yy zz
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// OpSpecConstantComposite tt xx yy zz;
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keys.push_back(static_cast<uint32_t>(inst.opcode()));
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for (const auto& operand : inst) {
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if (operand.type == SPV_OPERAND_TYPE_RESULT_ID) continue;
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keys.insert(keys.end(), operand.words.cbegin(), operand.words.cend());
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}
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return keys;
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}
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std::unique_ptr<Node> root_; // The root node of the trie.
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};
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} // anonymous namespace
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Pass::Status UnifyConstantPass::Process() {
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bool modified = false;
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ResultIdTrie defined_constants;
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for (Instruction *next_instruction,
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*inst = &*(context()->types_values_begin());
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inst; inst = next_instruction) {
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next_instruction = inst->NextNode();
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// Do not handle the instruction when there are decorations upon the result
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// id.
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if (get_def_use_mgr()->GetAnnotations(inst->result_id()).size() != 0) {
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continue;
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}
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// The overall algorithm is to store the result ids of all the eligible
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// constants encountered so far in a trie. For a constant defining
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// instruction under consideration, use its opcode, result type id and
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// words in operands as an array of keys to lookup the trie. If a result id
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// can be found for that array of keys, a constant with exactly the same
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// value must has been defined before, the constant under processing
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// should be replaced by the constant previously defined. If no such result
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// id can be found for that array of keys, this must be the first time a
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// constant with its value be defined, we then create a new trie node to
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// store the result id with the keys. When replacing a duplicated constant
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// with a previously defined constant, all the uses of the duplicated
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// constant, which must be placed after the duplicated constant defining
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// instruction, will be updated. This way, the descendants of the
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// previously defined constant and the duplicated constant will both refer
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// to the previously defined constant. So that the operand ids which are
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// used in key arrays will be the ids of the unified constants, when
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// processing is up to a descendant. This makes comparing the key array
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// always valid for judging duplication.
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switch (inst->opcode()) {
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case SpvOp::SpvOpConstantTrue:
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case SpvOp::SpvOpConstantFalse:
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case SpvOp::SpvOpConstant:
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case SpvOp::SpvOpConstantNull:
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case SpvOp::SpvOpConstantSampler:
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case SpvOp::SpvOpConstantComposite:
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// Only spec constants defined with OpSpecConstantOp and
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// OpSpecConstantComposite should be processed in this pass. Spec
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// constants defined with OpSpecConstant{|True|False} are decorated with
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// 'SpecId' decoration and all of them should be treated as unique.
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// 'SpecId' is not applicable to SpecConstants defined with
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// OpSpecConstant{Op|Composite}, their values are not necessary to be
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// unique. When all the operands/compoents are the same between two
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// OpSpecConstant{Op|Composite} results, their result values must be the
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// same so are unifiable.
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case SpvOp::SpvOpSpecConstantOp:
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case SpvOp::SpvOpSpecConstantComposite: {
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uint32_t id = defined_constants.LookupEquivalentResultFor(*inst);
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if (id != inst->result_id()) {
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// The constant is a duplicated one, use the cached constant to
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// replace the uses of this duplicated one, then turn it to nop.
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context()->ReplaceAllUsesWith(inst->result_id(), id);
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context()->KillInst(inst);
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modified = true;
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}
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break;
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}
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default:
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break;
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}
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}
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return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
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}
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} // namespace opt
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} // namespace spvtools
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