SPIRV-Tools/source/opt/eliminate_dead_constant_pass.cpp

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// 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 "ir_context.h"
#include "log.h"
#include "reflect.h"
namespace spvtools {
namespace opt {
Pass::Status EliminateDeadConstantPass::Process(ir::IRContext* irContext) {
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 = irContext->GetConstants();
for (auto* c : constants) {
uint32_t const_id = c->result_id();
size_t count = 0;
Adding new def -> use mapping container Replaced representation of uses * Changed uses from unordered_map<uint32_t, UseList> to set<pairInstruction*, Instruction*>> * Replaced GetUses with ForEachUser and ForEachUse functions * updated passes to use new functions * partially updated tests * lots of cleanup still todo Adding an unique id to Instruction generated by IRContext Each instruction is given an unique id that can be used for ordering purposes. The ids are generated via the IRContext. Major changes: * Instructions now contain a uint32_t for unique id and a cached context pointer * Most constructors have been modified to take a context as input * unfortunately I cannot remove the default and copy constructors, but developers should avoid these * Added accessors to parents of basic block and function * Removed the copy constructors for BasicBlock and Function and replaced them with Clone functions * Reworked BuildModule to return an IRContext owning the built module * Since all instructions require a context, the context now becomes the basic unit for IR * Added a constructor to context to create an owned module internally * Replaced uses of Instruction's copy constructor with Clone whereever I found them * Reworked the linker functionality to perform clones into a different context instead of moves * Updated many tests to be consistent with the above changes * Still need to add new tests to cover added functionality * Added comparison operators to Instruction Adding tests for Instruction, IRContext and IR loading Fixed some header comments for BuildModule Fixes to get tests passing again * Reordered two linker steps to avoid use/def problems * Fixed def/use manager uses in merge return pass * Added early return for GetAnnotations * Changed uses of Instruction::ToNop in passes to IRContext::KillInst Simplifying the uses for some contexts in passes
2017-11-14 19:11:50 +00:00
irContext->get_def_use_mgr()->ForEachUse(
const_id, [&count](ir::Instruction* user, uint32_t index) {
(void)index;
SpvOp op = user->opcode();
if (!(ir::IsAnnotationInst(op) || ir::IsDebug1Inst(op) ||
ir::IsDebug2Inst(op) || ir::IsDebug3Inst(op))) {
++count;
}
});
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 =
irContext->get_def_use_mgr()->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);
}
// Turn all dead instructions and uses of them to nop
for (auto* dc : dead_consts) {
irContext->KillDef(dc->result_id());
}
return dead_consts.empty() ? Status::SuccessWithoutChange
: Status::SuccessWithChange;
}
} // namespace opt
} // namespace spvtools