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// Copyright (c) 2018 Google LLC.
//
// 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 "source/opt/loop_fusion_pass.h"
#include "source/opt/loop_descriptor.h"
#include "source/opt/loop_fusion.h"
#include "source/opt/register_pressure.h"
namespace spvtools {
namespace opt {
Pass::Status LoopFusionPass::Process() {
Status status = Status::SuccessWithoutChange;
Module* module = context()->module();
// Process each function in the module
for (Function& f : *module) {
status = CombineStatus(status, ProcessFunction(&f));
if (status == Status::Failure) return Status::Failure;
}
return status;
}
Pass::Status LoopFusionPass::ProcessFunction(Function* function) {
LoopDescriptor& ld = *context()->GetLoopDescriptor(function);
// If a loop doesn't have a preheader needs then it needs to be created. Make
// sure to return Status::SuccessWithChange in that case.
bool modified = false;
auto status = ld.CreatePreHeaderBlocksIfMissing();
if (status == LoopDescriptor::Status::Failure) return Status::Failure;
modified = status == LoopDescriptor::Status::SuccessWithChange;
// TODO(tremmelg): Could the only loop that |loop| could possibly be fused be
// picked out so don't have to check every loop
for (auto& loop_0 : ld) {
for (auto& loop_1 : ld) {
LoopFusion fusion(context(), &loop_0, &loop_1);
if (fusion.AreCompatible() && fusion.IsLegal()) {
RegisterLiveness liveness(context(), function);
RegisterLiveness::RegionRegisterLiveness reg_pressure{};
liveness.SimulateFusion(loop_0, loop_1, ®_pressure);
if (reg_pressure.used_registers_ <= max_registers_per_loop_) {
fusion.Fuse();
// Recurse, as the current iterators will have been invalidated.
ProcessFunction(function);
return Status::SuccessWithChange;
}
}
}
}
return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
}
} // namespace opt
} // namespace spvtools
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