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https://github.com/KhronosGroup/SPIRV-Tools
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476cae6f7d
This is the first part of adding the IRContext. This class is meant to hold the extra data that is build on top of the module that it owns. The first part will simply create the IRContext class and get it passed to the passes in place of the module. For now it does not have any functionality of its own, but it acts more as a wrapper for the module. The functions that I added to the IRContext are those that either traverse the headers or add to them. I did this because we may decide to have other ways of dealing with these sections (for example adding a type pool, or use the decoration manager). I also added the function that add to the header because the IRContext needs to know when an instruction is added to update other data structures appropriately. Note that there is still lots of work that needs to be done. There are still many places that change the module, and do not inform the context. That will be the next step.
116 lines
4.1 KiB
C++
116 lines
4.1 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 "dead_variable_elimination.h"
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#include "reflect.h"
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namespace spvtools {
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namespace opt {
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// This optimization removes global variables that are not needed because they
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// are definitely not accessed.
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Pass::Status DeadVariableElimination::Process(ir::IRContext* c) {
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// The algorithm will compute the reference count for every global variable.
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// Anything with a reference count of 0 will then be deleted. For variables
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// that might have references that are not explicit in this context, we use the
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// value kMustKeep as the reference count.
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InitializeProcessing(c);
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// Decoration manager to help organize decorations.
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analysis::DecorationManager decoration_manager(context()->module());
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std::vector<uint32_t> ids_to_remove;
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// Get the reference count for all of the global OpVariable instructions.
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for (auto& inst : context()->types_values()) {
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if (inst.opcode() != SpvOp::SpvOpVariable) {
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continue;
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}
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size_t count = 0;
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uint32_t result_id = inst.result_id();
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// Check the linkage. If it is exported, it could be reference somewhere
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// else, so we must keep the variable around.
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decoration_manager.ForEachDecoration(
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result_id, SpvDecorationLinkageAttributes,
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[&count](const ir::Instruction& linkage_instruction) {
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uint32_t last_operand = linkage_instruction.NumOperands() - 1;
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if (linkage_instruction.GetSingleWordOperand(last_operand) ==
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SpvLinkageTypeExport) {
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count = kMustKeep;
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}
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});
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if (count != kMustKeep) {
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// If we don't have to keep the instruction for other reasons, then look
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// at the uses and count the number of real references.
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if (analysis::UseList* uses = get_def_use_mgr()->GetUses(result_id)) {
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count = std::count_if(
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uses->begin(), uses->end(), [](const analysis::Use& u) {
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return (!ir::IsAnnotationInst(u.inst->opcode()) &&
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u.inst->opcode() != SpvOpName);
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});
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}
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}
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reference_count_[result_id] = count;
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if (count == 0) {
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ids_to_remove.push_back(result_id);
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}
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}
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// Remove all of the variables that have a reference count of 0.
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bool modified = false;
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if (!ids_to_remove.empty()) {
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modified = true;
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for (auto result_id : ids_to_remove) {
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DeleteVariable(result_id);
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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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void DeadVariableElimination::DeleteVariable(uint32_t result_id) {
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ir::Instruction* inst = get_def_use_mgr()->GetDef(result_id);
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assert(inst->opcode() == SpvOpVariable &&
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"Should not be trying to delete anything other than an OpVariable.");
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// Look for an initializer that references another variable. We need to know
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// if that variable can be deleted after the reference is removed.
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if (inst->NumOperands() == 4) {
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ir::Instruction* initializer =
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get_def_use_mgr()->GetDef(inst->GetSingleWordOperand(3));
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// TODO: Handle OpSpecConstantOP which might be defined in terms of other
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// variables. Will probably require a unified dead code pass that does all
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// instruction types. (Issue 906)
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if (initializer->opcode() == SpvOpVariable) {
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uint32_t initializer_id = initializer->result_id();
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size_t& count = reference_count_[initializer_id];
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if (count != kMustKeep) {
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--count;
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}
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if (count == 0) {
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DeleteVariable(initializer_id);
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}
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}
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}
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this->KillNamesAndDecorates(result_id);
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get_def_use_mgr()->KillDef(result_id);
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}
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} // namespace opt
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} // namespace spvtools
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