internal/ceres/expression_ref.cc

// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2019 Google Inc. All rights reserved.
// http://code.google.com/p/ceres-solver/
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// Author: darius.rueckert@fau.de (Darius Rueckert)

#include "ceres/codegen/internal/expression_ref.h"

#include "ceres/codegen/internal/expression_graph.h"
#include "glog/logging.h"

namespace ceres {
namespace internal {

ExpressionRef AddExpressionToGraph(const Expression& expression) {
  ExpressionGraph* graph = GetCurrentExpressionGraph();
  CHECK(graph)
      << "The ExpressionGraph has to be created before using Expressions. This "
         "is achieved by calling ceres::StartRecordingExpressions.";
  return ExpressionRef::Create(graph->InsertBack(expression));
}

ExpressionRef ExpressionRef::Create(ExpressionId id) {
  ExpressionRef ref;
  ref.id = id;
  return ref;
}

ExpressionRef::ExpressionRef(double compile_time_constant) {
  id = AddExpressionToGraph(
           Expression::CreateCompileTimeConstant(compile_time_constant))
           .id;
}

ExpressionRef::ExpressionRef(const ExpressionRef& other) { *this = other; }

ExpressionRef& ExpressionRef::operator=(const ExpressionRef& other) {
  // Assigning an uninitialized variable to another variable is an error.
  CHECK(other.IsInitialized()) << "Uninitialized Assignment.";
  if (IsInitialized()) {
    // Create assignment from other -> this
    AddExpressionToGraph(Expression::CreateAssignment(this->id, other.id));
  } else {
    // Create a new variable and
    // Create assignment from other -> this
    // Passing kInvalidExpressionId to CreateAssignment generates a new
    // variable name which we store in the id.
    id = AddExpressionToGraph(
             Expression::CreateAssignment(kInvalidExpressionId, other.id))
             .id;
  }
  return *this;
}

ExpressionRef::ExpressionRef(ExpressionRef&& other) {
  *this = std::move(other);
}

ExpressionRef& ExpressionRef::operator=(ExpressionRef&& other) {
  // Assigning an uninitialized variable to another variable is an error.
  CHECK(other.IsInitialized()) << "Uninitialized Assignment.";

  if (IsInitialized()) {
    // Create assignment from other -> this
    AddExpressionToGraph(Expression::CreateAssignment(id, other.id));
  } else {
    // Special case: 'this' is uninitialized and other is an rvalue.
    //    -> Implement copy elision by only setting the reference
    // This reduces the number of generated expressions roughly by a factor
    // of 2. For example, in the following statement:
    //   T c = a + b;
    // The result of 'a + b' is an rvalue reference to ExpressionRef.
    // Therefore, the move constructor of 'c' is called. Since 'c' is also
    // uninitialized, this branch here is taken and the copy is removed. After
    // this function 'c' will just point to the temporary created by the 'a +
    // b' expression. This is valid, because we don't have any scoping
    // information and therefore assume global scope for all temporary
    // variables. The generated code for the single statement above, is:
    //   v_2 = v_0 + v_1;   // With c.id = 2
    // Without this move constructor the following two lines would be
    // generated:
    //   v_2 = v_0 + v_1;
    //   v_3 = v_2;        // With c.id = 3
    id = other.id;
  }
  other.id = kInvalidExpressionId;
  return *this;
}

// Compound operators
ExpressionRef& ExpressionRef::operator+=(const ExpressionRef& x) {
  *this = *this + x;
  return *this;
}

ExpressionRef& ExpressionRef::operator-=(const ExpressionRef& x) {
  *this = *this - x;
  return *this;
}

ExpressionRef& ExpressionRef::operator*=(const ExpressionRef& x) {
  *this = *this * x;
  return *this;
}

ExpressionRef& ExpressionRef::operator/=(const ExpressionRef& x) {
  *this = *this / x;
  return *this;
}

// Arith. Operators
ExpressionRef operator-(const ExpressionRef& x) {
  return AddExpressionToGraph(Expression::CreateUnaryArithmetic("-", x.id));
}

ExpressionRef operator+(const ExpressionRef& x) {
  return AddExpressionToGraph(Expression::CreateUnaryArithmetic("+", x.id));
}

ExpressionRef operator+(const ExpressionRef& x, const ExpressionRef& y) {
  return AddExpressionToGraph(
      Expression::CreateBinaryArithmetic("+", x.id, y.id));
}

ExpressionRef operator-(const ExpressionRef& x, const ExpressionRef& y) {
  return AddExpressionToGraph(
      Expression::CreateBinaryArithmetic("-", x.id, y.id));
}

ExpressionRef operator/(const ExpressionRef& x, const ExpressionRef& y) {
  return AddExpressionToGraph(
      Expression::CreateBinaryArithmetic("/", x.id, y.id));
}

ExpressionRef operator*(const ExpressionRef& x, const ExpressionRef& y) {
  return AddExpressionToGraph(
      Expression::CreateBinaryArithmetic("*", x.id, y.id));
}

ExpressionRef Ternary(const ComparisonExpressionRef& c,
                      const ExpressionRef& x,
                      const ExpressionRef& y) {
  return AddExpressionToGraph(
      Expression::CreateScalarFunctionCall("Ternary", {c.id, x.id, y.id}));
}

#define CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(op)         \
  ComparisonExpressionRef operator op(const ExpressionRef& x,   \
                                      const ExpressionRef& y) { \
    return ComparisonExpressionRef(AddExpressionToGraph(        \
        Expression::CreateBinaryCompare(#op, x.id, y.id)));     \
  }

#define CERES_DEFINE_EXPRESSION_LOGICAL_OPERATOR(op)                      \
  ComparisonExpressionRef operator op(const ComparisonExpressionRef& x,   \
                                      const ComparisonExpressionRef& y) { \
    return ComparisonExpressionRef(AddExpressionToGraph(                  \
        Expression::CreateBinaryCompare(#op, x.id, y.id)));               \
  }

CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(<)
CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(<=)
CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(>)
CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(>=)
CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(==)
CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(!=)
CERES_DEFINE_EXPRESSION_LOGICAL_OPERATOR(&&)
CERES_DEFINE_EXPRESSION_LOGICAL_OPERATOR(||)
CERES_DEFINE_EXPRESSION_LOGICAL_OPERATOR(&)
CERES_DEFINE_EXPRESSION_LOGICAL_OPERATOR(|)
#undef CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR
#undef CERES_DEFINE_EXPRESSION_LOGICAL_OPERATOR

ComparisonExpressionRef operator!(const ComparisonExpressionRef& x) {
  return ComparisonExpressionRef(
      AddExpressionToGraph(Expression::CreateLogicalNegation(x.id)));
}

}  // namespace internal
}  // namespace ceres