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/*
* Copyright (c) 2018 Samsung Electronics Co., Ltd. All Rights Reserved
*
* 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 "IdenticalObjectReduction.h"
#include "IRUtils.h"
#include <set>
namespace enco
{
void reduce_identical_object(enco::Code *code)
{
auto m = code->module();
std::set<coco::Copy *> detached;
// Preceding optimizations may generate "free" instructions.
// - i.e. an instruction not linked to a block
//
// Let's iterate over only a sequence of "bounded" instructions.
for (auto ins : instr_sequence(m))
{
assert(ins != nullptr);
assert(ins->parent() != nullptr);
auto copy = ins->asCopy();
if (copy == nullptr)
{
// Skip if instruction is not a copy
continue;
}
// TODO Support non-Feature Objects
auto ifm = copy->from()->asFeature();
auto ofm = copy->into()->asFeature();
assert(ofm->bag() != nullptr);
if (ifm->layout()->id() != ofm->layout()->id())
{
continue;
}
if (ifm->layout()->id() != coco::FeatureLayouts::BHWC::uid())
{
continue;
}
// Skip if this copy produces network output
if (ofm->bag()->output())
{
// TODO Optimize this case
//
// Note that the code under optimization is of the following form:
//
// %ifm <- Instr(...)
// %ofm <- Copy(%ifm)
//
// Let's assume that "Copy" is the only reader of %ifm (to be precise, its bag).
//
// Then, it is possible to rewrite the above fragment as follows:
//
// %ofm <- Instr(...)
//
continue;
}
if (ofm->bag()->reads()->size() > 0)
{
// Let us consider the following code:
//
// Bag:
// %bag_0 = Bag(...)
// %bag_1 = Bag(...)
// %bag_2 = Bag(...)
//
// Object:
// %obj_0 = FeatureObject(bag: %bag_0)
// %obj_1 = FeatureObject(bag: %bag_1)
//
// Instr:
// copy an object from %obj_0 into %obj_1
// shuffle values from %bag_1 into %bag_2
// eval Conv2D with %obj_1
//
// Identical Object Reduction (IOR) tries to eliminate the first copy via
// substitution (substitute all the occurrence of %obj_1 as use with %obj_0).
//
// Here is the code transformed by IOR:
//
// Bag:
// %bag_0 = Bag(...)
// %bag_1 = Bag(...)
// %bag_2 = Bag(...)
//
// Object:
// %obj_0 = FeatureObject(bag: %bag_0)
// %obj_1 = FeatureObject(bag: %bag_1)
//
// Instr:
// shuffle values from %bag_1 into %bag_2
// eval Conv2D with %obj_0
//
// Note that there is no updater of %bag_1 after IOR, and thus the behavior
// of the first shuffle instruction has changed.
//
// This examples shows that it is impossible to simply substitute %obj_1
// with %obj_0 in the presence of readers over its backing bag.
continue;
}
subst(copy->into(), copy->from());
copy->detach();
detached.insert(copy);
}
for (auto copy : detached)
{
m->entity()->instr()->destroy(copy);
}
}
} // namespace enco
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