include/ceres/codegen/internal/eliminate_nops.h

// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2020 Google Inc. All rights reserved.
// http://code.google.com/p/ceres-solver/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright notice,
//   this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
//   and/or other materials provided with the distribution.
// * Neither the name of Google Inc. nor the names of its contributors may be
//   used to endorse or promote products derived from this software without
//   specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
//
// Author: darius.rueckert@fau.de (Darius Rueckert)
//
#ifndef CERES_PUBLIC_CODEGEN_INTERNAL_ELIMINATE_NOPS_H_
#define CERES_PUBLIC_CODEGEN_INTERNAL_ELIMINATE_NOPS_H_

#include "ceres/codegen/internal/expression_graph.h"
#include "ceres/codegen/internal/optimization_pass_summary.h"

namespace ceres {
namespace internal {

// [OptimizationPass] NOP Cleanup
//
// Short Description:
//   Removes all expression with type==ExpressionType::NOP.
//
// Description:
//   Removing an expression not at the end requires reindexing of all later
//   expressions. Therefore, other optimization passes replace expression with
//   NOP instead of removing them. This optimization pass removes all NOPs back
//   to front.
//   The returned value is equal to the number of removed NOPs.
//
// Example:
//   v_0 = 1;
//   // NOP
//   v_2 = 2;
//   v_3 = v_0 + v_2
// Transforms to:
//   v_0 = 1;
//   v_1 = 2;
//   v_2 = v_0 + v_1;

OptimizationPassSummary EliminateNops(ExpressionGraph* graph);

}  // namespace internal
}  // namespace ceres

#endif  // CERES_PUBLIC_CODEGEN_INTERNAL_ELIMINATE_NOPS_H_