105 lines
3.7 KiB
C++
105 lines
3.7 KiB
C++
// 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/eliminate_dead_constant_pass.h"
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#include <algorithm>
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#include <unordered_map>
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#include <unordered_set>
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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/opt/log.h"
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#include "source/opt/reflect.h"
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namespace spvtools {
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namespace opt {
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Pass::Status EliminateDeadConstantPass::Process() {
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std::unordered_set<Instruction*> working_list;
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// Traverse all the instructions to get the initial set of dead constants as
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// working list and count number of real uses for constants. Uses in
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// annotation instructions do not count.
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std::unordered_map<Instruction*, size_t> use_counts;
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std::vector<Instruction*> constants = context()->GetConstants();
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for (auto* c : constants) {
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uint32_t const_id = c->result_id();
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size_t count = 0;
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context()->get_def_use_mgr()->ForEachUse(
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const_id, [&count](Instruction* user, uint32_t index) {
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(void)index;
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SpvOp op = user->opcode();
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if (!(IsAnnotationInst(op) || IsDebug1Inst(op) || IsDebug2Inst(op) ||
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IsDebug3Inst(op))) {
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++count;
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}
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});
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use_counts[c] = count;
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if (!count) {
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working_list.insert(c);
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}
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}
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// Start from the constants with 0 uses, back trace through the def-use chain
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// to find all dead constants.
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std::unordered_set<Instruction*> dead_consts;
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while (!working_list.empty()) {
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Instruction* inst = *working_list.begin();
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// Back propagate if the instruction contains IDs in its operands.
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switch (inst->opcode()) {
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case SpvOp::SpvOpConstantComposite:
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case SpvOp::SpvOpSpecConstantComposite:
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case SpvOp::SpvOpSpecConstantOp:
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for (uint32_t i = 0; i < inst->NumInOperands(); i++) {
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// SpecConstantOp instruction contains 'opcode' as its operand. Need
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// to exclude such operands when decreasing uses.
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if (inst->GetInOperand(i).type != SPV_OPERAND_TYPE_ID) {
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continue;
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}
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uint32_t operand_id = inst->GetSingleWordInOperand(i);
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Instruction* def_inst =
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context()->get_def_use_mgr()->GetDef(operand_id);
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// If the use_count does not have any count for the def_inst,
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// def_inst must not be a constant, and should be ignored here.
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if (!use_counts.count(def_inst)) {
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continue;
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}
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// The number of uses should never be less then 0, so it can not be
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// less than 1 before it decreases.
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SPIRV_ASSERT(consumer(), use_counts[def_inst] > 0);
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--use_counts[def_inst];
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if (!use_counts[def_inst]) {
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working_list.insert(def_inst);
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}
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}
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break;
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default:
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break;
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}
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dead_consts.insert(inst);
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working_list.erase(inst);
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}
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// Turn all dead instructions and uses of them to nop
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for (auto* dc : dead_consts) {
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context()->KillDef(dc->result_id());
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}
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return dead_consts.empty() ? Status::SuccessWithoutChange
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: Status::SuccessWithChange;
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}
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} // namespace opt
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} // namespace spvtools
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