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https://github.com/KhronosGroup/SPIRV-Tools
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78cf86150e
Id descriptors are computed as a recursive hash of all instructions used to define an id. Descriptors are invarint of actual id values and the similar code in different files would produce the same descriptors. Multiple ids can have the same descriptor. For example %1 = OpConstant %u32 1 %2 = OpConstant %u32 1 would produce two ids with the same descriptor. But %3 = OpConstant %s32 1 %4 = OpConstant %u32 2 would have descriptors different from %1 and %2. Descriptors will be used as handles of move-to-front sequences in SPIR-V compression.
79 lines
2.2 KiB
C++
79 lines
2.2 KiB
C++
// Copyright (c) 2017 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 "id_descriptor.h"
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#include <cassert>
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#include <iostream>
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#include "opcode.h"
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#include "operand.h"
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namespace libspirv {
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namespace {
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// Hashes an array of words. Order of words is important.
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uint32_t HashU32Array(const std::vector<uint32_t>& words) {
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// The hash function is a sum of hashes of each word seeded by word index.
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// Knuth's multiplicative hash is used to hash the words.
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const uint32_t kKnuthMulHash = 2654435761;
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uint32_t val = 0;
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for (uint32_t i = 0; i < words.size(); ++i) {
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val += (words[i] + i + 123) * kKnuthMulHash;
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}
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return val;
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}
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} // namespace
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uint32_t IdDescriptorCollection::ProcessInstruction(
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const spv_parsed_instruction_t& inst) {
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if (!inst.result_id)
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return 0;
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assert(words_.empty());
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words_.push_back(inst.words[0]);
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for (size_t operand_index = 0; operand_index < inst.num_operands;
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++operand_index) {
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const auto &operand = inst.operands[operand_index];
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if (spvIsIdType(operand.type)) {
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const uint32_t id = inst.words[operand.offset];
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const auto it = id_to_descriptor_.find(id);
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// Forward declared ids are not hashed.
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if (it != id_to_descriptor_.end()) {
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words_.push_back(it->second);
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}
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} else {
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for (size_t operand_word_index = 0;
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operand_word_index < operand.num_words; ++operand_word_index) {
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words_.push_back(inst.words[operand.offset + operand_word_index]);
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}
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}
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}
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const uint32_t descriptor = HashU32Array(words_);
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assert(descriptor);
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words_.clear();
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const auto result = id_to_descriptor_.emplace(inst.result_id, descriptor);
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assert(result.second);
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(void)result;
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return descriptor;
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}
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} // namespace libspirv
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