include/flang/Evaluate/shape.h

//===-- include/flang/Evaluate/shape.h --------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// GetShape() analyzes an expression and determines its shape, if possible,
// representing the result as a vector of scalar integer expressions.

#ifndef FORTRAN_EVALUATE_SHAPE_H_
#define FORTRAN_EVALUATE_SHAPE_H_

#include "expression.h"
#include "traverse.h"
#include "variable.h"
#include "flang/Common/indirection.h"
#include "flang/Evaluate/type.h"
#include <optional>
#include <variant>

namespace Fortran::parser {
class ContextualMessages;
}

namespace Fortran::evaluate {

class FoldingContext;

using ExtentType = SubscriptInteger;
using ExtentExpr = Expr<ExtentType>;
using MaybeExtentExpr = std::optional<ExtentExpr>;
using Shape = std::vector<MaybeExtentExpr>;

bool IsImpliedShape(const Symbol &);
bool IsExplicitShape(const Symbol &);

// Conversions between various representations of shapes.
std::optional<ExtentExpr> AsExtentArrayExpr(const Shape &);

std::optional<Constant<ExtentType>> AsConstantShape(
    FoldingContext &, const Shape &);
Constant<ExtentType> AsConstantShape(const ConstantSubscripts &);

ConstantSubscripts AsConstantExtents(const Constant<ExtentType> &);
std::optional<ConstantSubscripts> AsConstantExtents(
    FoldingContext &, const Shape &);
Shape AsShape(const ConstantSubscripts &);
std::optional<Shape> AsShape(const std::optional<ConstantSubscripts> &);

inline int GetRank(const Shape &s) { return static_cast<int>(s.size()); }

Shape Fold(FoldingContext &, Shape &&);
std::optional<Shape> Fold(FoldingContext &, std::optional<Shape> &&);

// Computes shapes in terms of expressions that are scope-invariant, by
// default, which is nearly always what one wants outside of procedure
// characterization.
template <typename A>
std::optional<Shape> GetShape(
    FoldingContext &, const A &, bool invariantOnly = true);
template <typename A>
std::optional<Shape> GetShape(const A &, bool invariantOnly = true);

// The dimension argument to these inquiries is zero-based,
// unlike the DIM= arguments to many intrinsics.
//
// GetRawLowerBound() returns a lower bound expression, which may
// not be suitable for all purposes; specifically, it might not be invariant
// in its scope, and it will not have been forced to 1 on an empty dimension.
// GetLBOUND()'s result is safer, but it is optional because it does fail
// in those circumstances.
// Similarly, GetUBOUND result will be forced to 0 on an empty dimension,
// but will fail if the extent is not a compile time constant.
ExtentExpr GetRawLowerBound(
    const NamedEntity &, int dimension, bool invariantOnly = true);
ExtentExpr GetRawLowerBound(FoldingContext &, const NamedEntity &,
    int dimension, bool invariantOnly = true);
MaybeExtentExpr GetLBOUND(
    const NamedEntity &, int dimension, bool invariantOnly = true);
MaybeExtentExpr GetLBOUND(FoldingContext &, const NamedEntity &, int dimension,
    bool invariantOnly = true);
MaybeExtentExpr GetRawUpperBound(
    const NamedEntity &, int dimension, bool invariantOnly = true);
MaybeExtentExpr GetRawUpperBound(FoldingContext &, const NamedEntity &,
    int dimension, bool invariantOnly = true);
MaybeExtentExpr GetUBOUND(
    const NamedEntity &, int dimension, bool invariantOnly = true);
MaybeExtentExpr GetUBOUND(FoldingContext &, const NamedEntity &, int dimension,
    bool invariantOnly = true);
MaybeExtentExpr ComputeUpperBound(ExtentExpr &&lower, MaybeExtentExpr &&extent);
MaybeExtentExpr ComputeUpperBound(
    FoldingContext &, ExtentExpr &&lower, MaybeExtentExpr &&extent);
Shape GetRawLowerBounds(const NamedEntity &, bool invariantOnly = true);
Shape GetRawLowerBounds(
    FoldingContext &, const NamedEntity &, bool invariantOnly = true);
Shape GetLBOUNDs(const NamedEntity &, bool invariantOnly = true);
Shape GetLBOUNDs(
    FoldingContext &, const NamedEntity &, bool invariantOnly = true);
Shape GetUBOUNDs(const NamedEntity &, bool invariantOnly = true);
Shape GetUBOUNDs(
    FoldingContext &, const NamedEntity &, bool invariantOnly = true);
MaybeExtentExpr GetExtent(
    const NamedEntity &, int dimension, bool invariantOnly = true);
MaybeExtentExpr GetExtent(FoldingContext &, const NamedEntity &, int dimension,
    bool invariantOnly = true);
MaybeExtentExpr GetExtent(const Subscript &, const NamedEntity &, int dimension,
    bool invariantOnly = true);
MaybeExtentExpr GetExtent(FoldingContext &, const Subscript &,
    const NamedEntity &, int dimension, bool invariantOnly = true);

// Compute an element count for a triplet or trip count for a DO.
ExtentExpr CountTrips(
    ExtentExpr &&lower, ExtentExpr &&upper, ExtentExpr &&stride);
ExtentExpr CountTrips(
    const ExtentExpr &lower, const ExtentExpr &upper, const ExtentExpr &stride);
MaybeExtentExpr CountTrips(
    MaybeExtentExpr &&lower, MaybeExtentExpr &&upper, MaybeExtentExpr &&stride);

// Computes SIZE() == PRODUCT(shape)
MaybeExtentExpr GetSize(Shape &&);
ConstantSubscript GetSize(const ConstantSubscripts &);

// Utility predicate: does an expression reference any implied DO index?
bool ContainsAnyImpliedDoIndex(const ExtentExpr &);

class GetShapeHelper
    : public AnyTraverse<GetShapeHelper, std::optional<Shape>> {
public:
  using Result = std::optional<Shape>;
  using Base = AnyTraverse<GetShapeHelper, Result>;
  using Base::operator();
  GetShapeHelper(FoldingContext *context, bool invariantOnly)
      : Base{*this}, context_{context}, invariantOnly_{invariantOnly} {}

  Result operator()(const ImpliedDoIndex &) const { return ScalarShape(); }
  Result operator()(const DescriptorInquiry &) const { return ScalarShape(); }
  Result operator()(const TypeParamInquiry &) const { return ScalarShape(); }
  Result operator()(const BOZLiteralConstant &) const { return ScalarShape(); }
  Result operator()(const StaticDataObject::Pointer &) const {
    return ScalarShape();
  }
  Result operator()(const StructureConstructor &) const {
    return ScalarShape();
  }

  template <typename T> Result operator()(const Constant<T> &c) const {
    return ConstantShape(c.SHAPE());
  }

  Result operator()(const Symbol &) const;
  Result operator()(const Component &) const;
  Result operator()(const ArrayRef &) const;
  Result operator()(const CoarrayRef &) const;
  Result operator()(const Substring &) const;
  Result operator()(const ProcedureRef &) const;

  template <typename T>
  Result operator()(const ArrayConstructor<T> &aconst) const {
    return Shape{GetArrayConstructorExtent(aconst)};
  }
  template <typename D, typename R, typename LO, typename RO>
  Result operator()(const Operation<D, R, LO, RO> &operation) const {
    if (operation.right().Rank() > 0) {
      return (*this)(operation.right());
    } else {
      return (*this)(operation.left());
    }
  }

private:
  static Result ScalarShape() { return Shape{}; }
  static Shape ConstantShape(const Constant<ExtentType> &);
  Result AsShapeResult(ExtentExpr &&) const;
  Shape CreateShape(int rank, NamedEntity &) const;

  template <typename T>
  MaybeExtentExpr GetArrayConstructorValueExtent(
      const ArrayConstructorValue<T> &value) const {
    return common::visit(
        common::visitors{
            [&](const Expr<T> &x) -> MaybeExtentExpr {
              if (auto xShape{(*this)(x)}) {
                // Array values in array constructors get linearized.
                return GetSize(std::move(*xShape));
              } else {
                return std::nullopt;
              }
            },
            [&](const ImpliedDo<T> &ido) -> MaybeExtentExpr {
              // Don't be heroic and try to figure out triangular implied DO
              // nests.
              if (!ContainsAnyImpliedDoIndex(ido.lower()) &&
                  !ContainsAnyImpliedDoIndex(ido.upper()) &&
                  !ContainsAnyImpliedDoIndex(ido.stride())) {
                if (auto nValues{GetArrayConstructorExtent(ido.values())}) {
                  if (!ContainsAnyImpliedDoIndex(*nValues)) {
                    return std::move(*nValues) *
                        CountTrips(ido.lower(), ido.upper(), ido.stride());
                  }
                }
              }
              return std::nullopt;
            },
        },
        value.u);
  }

  template <typename T>
  MaybeExtentExpr GetArrayConstructorExtent(
      const ArrayConstructorValues<T> &values) const {
    ExtentExpr result{0};
    for (const auto &value : values) {
      if (MaybeExtentExpr n{GetArrayConstructorValueExtent(value)}) {
        AccumulateExtent(result, std::move(*n));
      } else {
        return std::nullopt;
      }
    }
    return result;
  }

  // Add an extent to another, with folding
  void AccumulateExtent(ExtentExpr &, ExtentExpr &&) const;

  FoldingContext *context_{nullptr};
  mutable bool useResultSymbolShape_{true};
  // When invariantOnly=false, the returned shape need not be invariant
  // in its scope; in particular, it may contain references to dummy arguments.
  bool invariantOnly_{true};
};

template <typename A>
std::optional<Shape> GetShape(
    FoldingContext &context, const A &x, bool invariantOnly) {
  if (auto shape{GetShapeHelper{&context, invariantOnly}(x)}) {
    return Fold(context, std::move(shape));
  } else {
    return std::nullopt;
  }
}

template <typename A>
std::optional<Shape> GetShape(const A &x, bool invariantOnly) {
  return GetShapeHelper{/*context=*/nullptr, invariantOnly}(x);
}

template <typename A>
std::optional<Shape> GetShape(
    FoldingContext *context, const A &x, bool invariantOnly = true) {
  return GetShapeHelper{context, invariantOnly}(x);
}

template <typename A>
std::optional<Constant<ExtentType>> GetConstantShape(
    FoldingContext &context, const A &x) {
  if (auto shape{GetShape(context, x, /*invariantonly=*/true)}) {
    return AsConstantShape(context, *shape);
  } else {
    return std::nullopt;
  }
}

template <typename A>
std::optional<ConstantSubscripts> GetConstantExtents(
    FoldingContext &context, const A &x) {
  if (auto shape{GetShape(context, x, /*invariantOnly=*/true)}) {
    return AsConstantExtents(context, *shape);
  } else {
    return std::nullopt;
  }
}

// Get shape that does not depends on callee scope symbols if the expression
// contains calls. Return std::nullopt if it is not possible to build such shape
// (e.g. for calls to array-valued functions whose result shape depends on the
// arguments).
template <typename A>
std::optional<Shape> GetContextFreeShape(FoldingContext &context, const A &x) {
  return GetShapeHelper{&context, /*invariantOnly=*/true}(x);
}

// Compilation-time shape conformance checking, when corresponding extents
// are or should be known.  The result is an optional Boolean:
//  - nullopt: no error found or reported, but conformance cannot
//    be guaranteed during compilation; this result is possible only
//    when one or both arrays are allowed to have deferred shape
//  - true: no error found or reported, arrays conform
//  - false: errors found and reported
// Use "CheckConformance(...).value_or()" to specify a default result
// when you don't care whether messages have been emitted.
struct CheckConformanceFlags {
  enum Flags {
    None = 0,
    LeftScalarExpandable = 1,
    RightScalarExpandable = 2,
    LeftIsDeferredShape = 4,
    RightIsDeferredShape = 8,
    EitherScalarExpandable = LeftScalarExpandable | RightScalarExpandable,
    BothDeferredShape = LeftIsDeferredShape | RightIsDeferredShape,
    RightIsExpandableDeferred = RightScalarExpandable | RightIsDeferredShape,
  };
};
std::optional<bool> CheckConformance(parser::ContextualMessages &,
    const Shape &left, const Shape &right,
    CheckConformanceFlags::Flags flags = CheckConformanceFlags::None,
    const char *leftIs = "left operand", const char *rightIs = "right operand");

// Increments one-based subscripts in element order (first varies fastest)
// and returns true when they remain in range; resets them all to one and
// return false otherwise (including the case where one or more of the
// extents are zero).
bool IncrementSubscripts(
    ConstantSubscripts &, const ConstantSubscripts &extents);

} // namespace Fortran::evaluate
#endif // FORTRAN_EVALUATE_SHAPE_H_