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https://github.com/KhronosGroup/SPIRV-Tools
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28c415500d
Creates a pass that removes redundant instructions within the same basic block. This will be implemented using a hash based value numbering algorithm. Added a number of functions that check for the Vulkan descriptor types. These are used to determine if we are variables are read-only or not. Implemented a function to check if loads and variables are read-only. Implemented kernel specific and shader specific versions. A big change is that the Combinator analysis in ADCE is factored out into the IRContext as an analysis. This was done because it is being reused in the value number table.
90 lines
3.1 KiB
C++
90 lines
3.1 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 "local_redundancy_elimination.h"
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#include "value_number_table.h"
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namespace spvtools {
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namespace opt {
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Pass::Status LocalRedundancyEliminationPass::Process(ir::IRContext* c) {
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InitializeProcessing(c);
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bool modified = false;
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for (auto& func : *get_module()) {
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for (auto& bb : func) {
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// Resetting the value number table for every basic block because we just
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// want the opportunities within a basic block. This will help keep
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// register pressure down.
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ValueNumberTable vnTable(context());
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// Keeps track of all ids that contain a given value number. We keep
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// track of multiple values because they could have the same value, but
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// different decorations.
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std::vector<std::vector<uint32_t>> value_to_ids;
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if (EliminateRedundanciesInBB(&bb, &vnTable, &value_to_ids))
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modified = true;
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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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bool LocalRedundancyEliminationPass::EliminateRedundanciesInBB(
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ir::BasicBlock* block, ValueNumberTable* vnTable,
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std::vector<std::vector<uint32_t>>* value_to_ids) {
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bool modified = false;
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auto func = [this, vnTable, &modified, value_to_ids](ir::Instruction* inst) {
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if (inst->result_id() == 0) {
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return;
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}
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uint32_t value = vnTable->GetValueNumber(inst);
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if (value >= value_to_ids->size()) {
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value_to_ids->resize(value + 1);
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}
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// Now that we have the value number of the instruction, we use
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// |value_to_ids| to get other ids that contain the same value. If we can
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// find an id in that set which has the same decorations, we can replace all
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// uses of the result of |inst| by that id.
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std::vector<uint32_t>& candidate_set = (*value_to_ids)[value];
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bool found_replacement = false;
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for (uint32_t candidate_id : candidate_set) {
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if (get_decoration_mgr()->HaveTheSameDecorations(inst->result_id(),
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candidate_id)) {
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context()->KillNamesAndDecorates(inst);
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context()->ReplaceAllUsesWith(inst->result_id(), candidate_id);
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context()->KillInst(inst);
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modified = true;
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found_replacement = true;
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break;
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}
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}
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// If we did not find a replacement, then add it as a candidate for later
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// instructions.
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if (!found_replacement) {
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candidate_set.push_back(inst->result_id());
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}
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};
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block->ForEachInst(func);
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return modified;
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}
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} // namespace opt
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} // namespace spvtools
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