SPIRV-Tools/source/opt/eliminate_dead_constant_pass.cpp

118 lines
4.1 KiB
C++

// Copyright (c) 2016 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "eliminate_dead_constant_pass.h"
#include <algorithm>
#include <unordered_map>
#include <unordered_set>
#include "def_use_manager.h"
#include "log.h"
#include "reflect.h"
namespace spvtools {
namespace opt {
Pass::Status EliminateDeadConstantPass::Process(ir::Module* module) {
analysis::DefUseManager def_use(consumer(), module);
std::unordered_set<ir::Instruction*> working_list;
// Traverse all the instructions to get the initial set of dead constants as
// working list and count number of real uses for constants. Uses in
// annotation instructions do not count.
std::unordered_map<ir::Instruction*, size_t> use_counts;
std::vector<ir::Instruction*> constants = module->GetConstants();
for (auto* c : constants) {
uint32_t const_id = c->result_id();
size_t count = 0;
if (analysis::UseList* uses = def_use.GetUses(const_id)) {
count =
std::count_if(uses->begin(), uses->end(), [](const analysis::Use& u) {
return !(ir::IsAnnotationInst(u.inst->opcode()) ||
ir::IsDebugInst(u.inst->opcode()));
});
}
use_counts[c] = count;
if (!count) {
working_list.insert(c);
}
}
// Start from the constants with 0 uses, back trace through the def-use chain
// to find all dead constants.
std::unordered_set<ir::Instruction*> dead_consts;
while (!working_list.empty()) {
ir::Instruction* inst = *working_list.begin();
// Back propagate if the instruction contains IDs in its operands.
switch (inst->opcode()) {
case SpvOp::SpvOpConstantComposite:
case SpvOp::SpvOpSpecConstantComposite:
case SpvOp::SpvOpSpecConstantOp:
for (uint32_t i = 0; i < inst->NumInOperands(); i++) {
// SpecConstantOp instruction contains 'opcode' as its operand. Need
// to exclude such operands when decreasing uses.
if (inst->GetInOperand(i).type != SPV_OPERAND_TYPE_ID) {
continue;
}
uint32_t operand_id = inst->GetSingleWordInOperand(i);
ir::Instruction* def_inst = def_use.GetDef(operand_id);
// If the use_count does not have any count for the def_inst,
// def_inst must not be a constant, and should be ignored here.
if (!use_counts.count(def_inst)) {
continue;
}
// The number of uses should never be less then 0, so it can not be
// less than 1 before it decreases.
SPIRV_ASSERT(consumer(), use_counts[def_inst] > 0);
--use_counts[def_inst];
if (!use_counts[def_inst]) {
working_list.insert(def_inst);
}
}
break;
default:
break;
}
dead_consts.insert(inst);
working_list.erase(inst);
}
// Find all annotation and debug instructions that are referencing dead
// constants.
std::unordered_set<ir::Instruction*> dead_others;
for (auto* dc : dead_consts) {
if (analysis::UseList* uses = def_use.GetUses(dc->result_id())) {
for (const auto& u : *uses) {
if (ir::IsAnnotationInst(u.inst->opcode()) ||
ir::IsDebugInst(u.inst->opcode())) {
dead_others.insert(u.inst);
}
}
}
}
// Turn all dead instructions and uses of them to nop
for (auto* dc : dead_consts) {
def_use.KillDef(dc->result_id());
}
for (auto* da : dead_others) {
da->ToNop();
}
return dead_consts.empty() ? Status::SuccessWithoutChange
: Status::SuccessWithChange;
}
} // namespace opt
} // namespace spvtools