lib/evaluate/variable.h

// Copyright (c) 2018-2019, NVIDIA CORPORATION.  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.

#ifndef FORTRAN_EVALUATE_VARIABLE_H_
#define FORTRAN_EVALUATE_VARIABLE_H_

// Defines data structures to represent data access and function calls
// for use in expressions and assignment statements.  Both copy and move
// semantics are supported.  The representation adheres closely to the
// Fortran 2018 language standard (q.v.) and uses strong typing to ensure
// that only admissable combinations can be constructed.

#include "call.h"
#include "common.h"
#include "formatting.h"
#include "static-data.h"
#include "type.h"
#include "../common/idioms.h"
#include "../common/template.h"
#include "../parser/char-block.h"
#include <optional>
#include <ostream>
#include <variant>
#include <vector>

namespace Fortran::semantics {
class Symbol;
}

namespace Fortran::evaluate {

using semantics::Symbol;

// Forward declarations
struct DataRef;
template<typename A> struct Variable;

// Reference a base object in memory.  This can be a Fortran symbol,
// static data (e.g., CHARACTER literal), or compiler-created temporary.
struct BaseObject {
  CLASS_BOILERPLATE(BaseObject)
  explicit BaseObject(const Symbol &symbol) : u{&symbol} {}
  explicit BaseObject(StaticDataObject::Pointer &&p) : u{std::move(p)} {}
  int Rank() const;
  std::optional<Expr<SubscriptInteger>> LEN() const;
  bool operator==(const BaseObject &) const;
  std::ostream &AsFortran(std::ostream &) const;
  const Symbol *symbol() const {
    if (const auto *result{std::get_if<const Symbol *>(&u)}) {
      return *result;
    } else {
      return nullptr;
    }
  }
  std::variant<const Symbol *, StaticDataObject::Pointer> u;
};

// R913 structure-component & C920: Defined to be a multi-part
// data-ref whose last part has no subscripts (or image-selector, although
// that isn't explicit in the document).  Pointer and allocatable components
// are not explicitly indirected in this representation.
// Complex components (%RE, %IM) are isolated below in ComplexPart.
// (Type parameter inquiries look like component references but are distinct
// constructs and not represented by this class.)
class Component {
public:
  CLASS_BOILERPLATE(Component)
  Component(const DataRef &b, const Symbol &c) : base_{b}, symbol_{&c} {}
  Component(DataRef &&b, const Symbol &c) : base_{std::move(b)}, symbol_{&c} {}
  Component(common::CopyableIndirection<DataRef> &&b, const Symbol &c)
    : base_{std::move(b)}, symbol_{&c} {}

  const DataRef &base() const { return base_.value(); }
  DataRef &base() { return base_.value(); }
  int Rank() const;
  const Symbol &GetFirstSymbol() const;
  const Symbol &GetLastSymbol() const { return *symbol_; }
  std::optional<Expr<SubscriptInteger>> LEN() const;
  bool operator==(const Component &) const;
  std::ostream &AsFortran(std::ostream &) const;

private:
  common::CopyableIndirection<DataRef> base_;
  const Symbol *symbol_;
};

// A NamedEntity is either a whole Symbol or a component in an instance
// of a derived type.  It may be a descriptor.
// TODO: this is basically a symbol with an optional DataRef base;
// could be used to replace Component.
class NamedEntity {
public:
  CLASS_BOILERPLATE(NamedEntity)
  explicit NamedEntity(const Symbol &symbol) : u_{&symbol} {}
  explicit NamedEntity(Component &&c) : u_{std::move(c)} {}

  bool IsSymbol() const { return std::holds_alternative<const Symbol *>(u_); }
  const Symbol &GetFirstSymbol() const;
  const Symbol &GetLastSymbol() const;
  const Component &GetComponent() const { return std::get<Component>(u_); }
  Component &GetComponent() { return std::get<Component>(u_); }
  const Component *UnwrapComponent() const;  // null if just a Symbol
  Component *UnwrapComponent();

  int Rank() const;
  std::optional<Expr<SubscriptInteger>> LEN() const;
  bool operator==(const NamedEntity &) const;
  std::ostream &AsFortran(std::ostream &) const;

private:
  std::variant<const Symbol *, Component> u_;
};

// R916 type-param-inquiry
// N.B. x%LEN for CHARACTER is rewritten in semantics to LEN(x), which is
// then handled via LEN() member functions in the various classes.
// x%KIND for intrinsic types is similarly rewritten in semantics to
// KIND(x), which is then folded to a constant value.
// "Bare" type parameter references within a derived type definition do
// not have base objects.
template<int KIND> class TypeParamInquiry {
public:
  using Result = Type<TypeCategory::Integer, KIND>;
  CLASS_BOILERPLATE(TypeParamInquiry)
  TypeParamInquiry(NamedEntity &&x, const Symbol &param)
    : base_{std::move(x)}, parameter_{&param} {}
  TypeParamInquiry(std::optional<NamedEntity> &&x, const Symbol &param)
    : base_{std::move(x)}, parameter_{&param} {}

  const std::optional<NamedEntity> &base() const { return base_; }
  std::optional<NamedEntity> &base() { return base_; }
  const Symbol &parameter() const { return *parameter_; }

  static constexpr int Rank() { return 0; }  // always scalar
  bool operator==(const TypeParamInquiry &) const;
  std::ostream &AsFortran(std::ostream &) const;

private:
  std::optional<NamedEntity> base_;
  const Symbol *parameter_;
};

EXPAND_FOR_EACH_INTEGER_KIND(
    TEMPLATE_INSTANTIATION, extern template class TypeParamInquiry, )

// R921 subscript-triplet
class Triplet {
public:
  Triplet();
  DEFAULT_CONSTRUCTORS_AND_ASSIGNMENTS(Triplet)
  Triplet(std::optional<Expr<SubscriptInteger>> &&,
      std::optional<Expr<SubscriptInteger>> &&,
      std::optional<Expr<SubscriptInteger>> &&);

  std::optional<Expr<SubscriptInteger>> lower() const;
  Triplet &set_lower(Expr<SubscriptInteger> &&);
  std::optional<Expr<SubscriptInteger>> upper() const;
  Triplet &set_upper(Expr<SubscriptInteger> &&);
  Expr<SubscriptInteger> stride() const;  // N.B. result is not optional<>
  Triplet &set_stride(Expr<SubscriptInteger> &&);

  bool operator==(const Triplet &) const;
  bool IsStrideOne() const;
  std::ostream &AsFortran(std::ostream &) const;

private:
  std::optional<IndirectSubscriptIntegerExpr> lower_, upper_;
  IndirectSubscriptIntegerExpr stride_;
};

// R919 subscript when rank 0, R923 vector-subscript when rank 1
struct Subscript {
  EVALUATE_UNION_CLASS_BOILERPLATE(Subscript)
  explicit Subscript(Expr<SubscriptInteger> &&s)
    : u{IndirectSubscriptIntegerExpr::Make(std::move(s))} {}
  int Rank() const;
  std::ostream &AsFortran(std::ostream &) const;
  std::variant<IndirectSubscriptIntegerExpr, Triplet> u;
};

// R917 array-element, R918 array-section; however, the case of an
// array-section that is a complex-part-designator is represented here
// as a ComplexPart instead.  C919 & C925 require that at most one set of
// subscripts have rank greater than 0, but that is not explicit in
// these types.
class ArrayRef {
public:
  CLASS_BOILERPLATE(ArrayRef)
  ArrayRef(const Symbol &symbol, std::vector<Subscript> &&ss)
    : base_{symbol}, subscript_(std::move(ss)) {}
  ArrayRef(Component &&c, std::vector<Subscript> &&ss)
    : base_{std::move(c)}, subscript_(std::move(ss)) {}
  ArrayRef(NamedEntity &&base, std::vector<Subscript> &&ss)
    : base_{std::move(base)}, subscript_(std::move(ss)) {}

  NamedEntity &base() { return base_; }
  const NamedEntity &base() const { return base_; }
  std::vector<Subscript> &subscript() { return subscript_; }
  const std::vector<Subscript> &subscript() const { return subscript_; }

  int size() const { return static_cast<int>(subscript_.size()); }
  Subscript &at(int n) { return subscript_.at(n); }
  const Subscript &at(int n) const { return subscript_.at(n); }
  template<typename A> common::IfNoLvalue<Subscript &, A> emplace_back(A &&x) {
    return subscript_.emplace_back(std::move(x));
  }

  int Rank() const;
  const Symbol &GetFirstSymbol() const;
  const Symbol &GetLastSymbol() const;
  std::optional<Expr<SubscriptInteger>> LEN() const;
  bool operator==(const ArrayRef &) const;
  std::ostream &AsFortran(std::ostream &) const;

private:
  NamedEntity base_;
  std::vector<Subscript> subscript_;
};

// R914 coindexed-named-object
// R924 image-selector, R926 image-selector-spec.
// C824 severely limits the usage of derived types with coarray ultimate
// components: they can't be pointers, allocatables, arrays, coarrays, or
// function results.  They can be components of other derived types.
// Although the F'2018 Standard never prohibits multiple image-selectors
// per se in the same data-ref or designator, nor the presence of an
// image-selector after a part-ref with rank, the constraints on the
// derived types that would have be involved make it impossible to declare
// an object that could be referenced in these ways (esp. C748 & C825).
// C930 precludes having both TEAM= and TEAM_NUMBER=.
// TODO C931 prohibits the use of a coindexed object as a stat-variable.
class CoarrayRef {
public:
  CLASS_BOILERPLATE(CoarrayRef)
  CoarrayRef(std::vector<const Symbol *> &&, std::vector<Subscript> &&,
      std::vector<Expr<SubscriptInteger>> &&);

  const std::vector<const Symbol *> &base() const { return base_; }
  std::vector<const Symbol *> &base() { return base_; }
  const std::vector<Subscript> &subscript() const { return subscript_; }
  std::vector<Subscript> &subscript() { return subscript_; }
  const std::vector<Expr<SubscriptInteger>> &cosubscript() const {
    return cosubscript_;
  }
  std::vector<Expr<SubscriptInteger>> &cosubscript() { return cosubscript_; }

  // These integral expressions for STAT= and TEAM= must be variables
  // (i.e., Designator or pointer-valued FunctionRef).
  std::optional<Expr<SomeInteger>> stat() const;
  CoarrayRef &set_stat(Expr<SomeInteger> &&);
  std::optional<Expr<SomeInteger>> team() const;
  bool teamIsTeamNumber() const { return teamIsTeamNumber_; }
  CoarrayRef &set_team(Expr<SomeInteger> &&, bool isTeamNumber = false);

  int Rank() const;
  const Symbol &GetFirstSymbol() const;
  const Symbol &GetLastSymbol() const;
  NamedEntity GetBase() const;
  std::optional<Expr<SubscriptInteger>> LEN() const;
  bool operator==(const CoarrayRef &) const;
  std::ostream &AsFortran(std::ostream &) const;

private:
  std::vector<const Symbol *> base_;
  std::vector<Subscript> subscript_;
  std::vector<Expr<SubscriptInteger>> cosubscript_;
  std::optional<common::CopyableIndirection<Expr<SomeInteger>>> stat_, team_;
  bool teamIsTeamNumber_{false};  // false: TEAM=, true: TEAM_NUMBER=
};

// R911 data-ref is defined syntactically as a series of part-refs, which
// would be far too expressive if the constraints were ignored.  Here, the
// possible outcomes are spelled out.  Note that a data-ref cannot include
// a terminal substring range or complex component designator; use
// R901 designator for that.
struct DataRef {
  EVALUATE_UNION_CLASS_BOILERPLATE(DataRef)
  explicit DataRef(const Symbol &n) : u{&n} {}

  int Rank() const;
  const Symbol &GetFirstSymbol() const;
  const Symbol &GetLastSymbol() const;
  std::optional<Expr<SubscriptInteger>> LEN() const;
  std::ostream &AsFortran(std::ostream &) const;

  std::variant<const Symbol *, Component, ArrayRef, CoarrayRef> u;
};

// R908 substring, R909 parent-string, R910 substring-range.
// The base object of a substring can be a literal.
// In the F2018 standard, substrings of array sections are parsed as
// variants of sections instead.
class Substring {
  using Parent = std::variant<DataRef, StaticDataObject::Pointer>;

public:
  CLASS_BOILERPLATE(Substring)
  Substring(DataRef &&parent, std::optional<Expr<SubscriptInteger>> &&lower,
      std::optional<Expr<SubscriptInteger>> &&upper)
    : parent_{std::move(parent)} {
    SetBounds(lower, upper);
  }
  Substring(StaticDataObject::Pointer &&parent,
      std::optional<Expr<SubscriptInteger>> &&lower,
      std::optional<Expr<SubscriptInteger>> &&upper)
    : parent_{std::move(parent)} {
    SetBounds(lower, upper);
  }

  Expr<SubscriptInteger> lower() const;
  Substring &set_lower(Expr<SubscriptInteger> &&);
  std::optional<Expr<SubscriptInteger>> upper() const;
  Substring &set_upper(Expr<SubscriptInteger> &&);
  const Parent &parent() const { return parent_; }
  Parent &parent() { return parent_; }

  int Rank() const;
  template<typename A> const A *GetParentIf() const {
    return std::get_if<A>(&parent_);
  }
  BaseObject GetBaseObject() const;
  const Symbol *GetLastSymbol() const;
  std::optional<Expr<SubscriptInteger>> LEN() const;
  bool operator==(const Substring &) const;
  std::ostream &AsFortran(std::ostream &) const;

  std::optional<Expr<SomeCharacter>> Fold(FoldingContext &);

private:
  void SetBounds(std::optional<Expr<SubscriptInteger>> &,
      std::optional<Expr<SubscriptInteger>> &);
  Parent parent_;
  std::optional<IndirectSubscriptIntegerExpr> lower_, upper_;
};

// R915 complex-part-designator
// In the F2018 standard, complex parts of array sections are parsed as
// variants of sections instead.
class ComplexPart {
public:
  ENUM_CLASS(Part, RE, IM)
  CLASS_BOILERPLATE(ComplexPart)
  ComplexPart(DataRef &&z, Part p) : complex_{std::move(z)}, part_{p} {}
  const DataRef &complex() const { return complex_; }
  Part part() const { return part_; }
  int Rank() const;
  const Symbol &GetFirstSymbol() const { return complex_.GetFirstSymbol(); }
  const Symbol &GetLastSymbol() const { return complex_.GetLastSymbol(); }
  bool operator==(const ComplexPart &) const;
  std::ostream &AsFortran(std::ostream &) const;

private:
  DataRef complex_;
  Part part_;
};

// R901 designator is the most general data reference object, apart from
// calls to pointer-valued functions.  Its variant holds everything that
// a DataRef can, and possibly also a substring reference or a
// complex component (%RE/%IM) reference.
template<typename T> class Designator {
  using DataRefs = std::decay_t<decltype(DataRef::u)>;
  using MaybeSubstring =
      std::conditional_t<T::category == TypeCategory::Character,
          std::variant<Substring>, std::variant<>>;
  using MaybeComplexPart = std::conditional_t<T::category == TypeCategory::Real,
      std::variant<ComplexPart>, std::variant<>>;
  using Variant =
      common::CombineVariants<DataRefs, MaybeSubstring, MaybeComplexPart>;

public:
  using Result = T;
  static_assert(
      IsSpecificIntrinsicType<Result> || std::is_same_v<Result, SomeDerived>);
  EVALUATE_UNION_CLASS_BOILERPLATE(Designator)

  Designator(const DataRef &that) : u{common::CopyVariant<Variant>(that.u)} {}
  Designator(DataRef &&that)
    : u{common::MoveVariant<Variant>(std::move(that.u))} {}

  std::optional<DynamicType> GetType() const;
  int Rank() const;
  BaseObject GetBaseObject() const;
  const Symbol *GetLastSymbol() const;
  std::optional<Expr<SubscriptInteger>> LEN() const;
  std::ostream &AsFortran(std::ostream &o) const;

  Variant u;
};

FOR_EACH_CHARACTER_KIND(extern template class Designator, )

template<typename T> struct Variable {
  using Result = T;
  static_assert(IsSpecificIntrinsicType<Result> ||
      std::is_same_v<Result, SomeKind<TypeCategory::Derived>>);
  EVALUATE_UNION_CLASS_BOILERPLATE(Variable)
  std::optional<DynamicType> GetType() const {
    return std::visit([](const auto &x) { return x.GetType(); }, u);
  }
  int Rank() const {
    return std::visit([](const auto &x) { return x.Rank(); }, u);
  }
  std::ostream &AsFortran(std::ostream &o) const {
    std::visit([&](const auto &x) { x.AsFortran(o); }, u);
    return o;
  }
  std::variant<Designator<Result>, FunctionRef<Result>> u;
};

class DescriptorInquiry {
public:
  using Result = SubscriptInteger;
  ENUM_CLASS(Field, LowerBound, Extent, Stride, Rank)

  CLASS_BOILERPLATE(DescriptorInquiry)
  DescriptorInquiry(const NamedEntity &, Field, int);
  DescriptorInquiry(NamedEntity &&, Field, int);

  NamedEntity &base() { return base_; }
  const NamedEntity &base() const { return base_; }
  Field field() const { return field_; }
  int dimension() const { return dimension_; }

  static constexpr int Rank() { return 0; }  // always scalar
  bool operator==(const DescriptorInquiry &) const;
  std::ostream &AsFortran(std::ostream &) const;

private:
  NamedEntity base_;
  Field field_;
  int dimension_{0};  // zero-based
};

#define INSTANTIATE_VARIABLE_TEMPLATES \
  EXPAND_FOR_EACH_INTEGER_KIND( \
      TEMPLATE_INSTANTIATION, template class TypeParamInquiry, ) \
  FOR_EACH_SPECIFIC_TYPE(template class Designator, )
}
#endif  // FORTRAN_EVALUATE_VARIABLE_H_