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//===------ VirtualInstruction.cpp ------------------------------*- 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

//

//===----------------------------------------------------------------------===//

//

// Tools for determining which instructions are within a statement and the

// nature of their operands.

//

//===----------------------------------------------------------------------===//

#ifndef POLLY_SUPPORT_VIRTUALINSTRUCTION_H

#define POLLY_SUPPORT_VIRTUALINSTRUCTION_H

#include "polly/ScopInfo.h"

namespace polly {

using llvm::User;

/// Determine the nature of a value's use within a statement.

///

/// These are not always representable by llvm::Use. For instance, scalar write

/// MemoryAccesses do use a value, but are not associated with an instruction's

/// argument.

///

/// Despite its name it is not tied to virtual instructions (although it works

/// fine with them), but to promote consistent handling of values used in

/// statements.

class VirtualUse final {

public:

  /// The different types of uses. Handling usually differentiates a lot between

  /// these; one can use a switch to handle each case (and get warned by the

  /// compiler if one is not handled).

  enum UseKind {

    // An llvm::Constant.

    Constant,

    // An llvm::BasicBlock.

    Block,

    // A value that can be generated using ScopExpander.

    Synthesizable,

    // A load that always reads the same value throughout the SCoP (address and

    // the value located there a SCoP-invariant) and has been hoisted in front

    // of the SCoP.

    Hoisted,

    // Definition before the SCoP and not synthesizable. Can be an instruction

    // outside the SCoP, a function argument or a global value. Whether there is

    // a scalar MemoryAccess in this statement for reading it depends on the

    // -polly-analyze-read-only-scalars switch.

    ReadOnly,

    // A definition within the same statement. No MemoryAccess between

    // definition and use are necessary.

    Intra,

    // Definition in another statement. There is a scalar MemoryAccess that

    // makes it available in this statement.

    Inter

  };

private:

  /// The statement where a value is used.

  ScopStmt *User;

  /// The value that is used.

  Value *Val;

  /// The type of value use.

  UseKind Kind;

  /// The value represented as llvm::SCEV expression.

  const SCEV *ScevExpr;

  /// If this is an inter-statement (or read-only) use, contains the

  /// MemoryAccess that makes the value available in this statement. In case of

  /// intra-statement uses, can contain a MemoryKind::Array access. In all other

  /// cases, it is a nullptr.

  MemoryAccess *InputMA;

  VirtualUse(ScopStmt *User, Value *Val, UseKind Kind, const SCEV *ScevExpr,

             MemoryAccess *InputMA)

      : User(User), Val(Val), Kind(Kind), ScevExpr(ScevExpr), InputMA(InputMA) {

  }

public:

  /// Get a VirtualUse for an llvm::Use.

  ///

  /// @param S       The Scop object.

  /// @param U       The llvm::Use the get information for.

  /// @param LI      The LoopInfo analysis. Needed to determine whether the

  ///                value is synthesizable.

  /// @param Virtual Whether to ignore existing MemoryAccess.

  ///

  /// @return The VirtualUse representing the same use as @p U.

  static VirtualUse create(Scop *S, const Use &U, LoopInfo *LI, bool Virtual);

  /// Get a VirtualUse for uses within statements.

  ///

  /// It is assumed that the user is not a PHINode. Such uses are always

  /// VirtualUse::Inter unless in a regions statement.

  ///

  /// @param S         The Scop object.

  /// @param UserStmt  The statement in which @p Val is used. Can be nullptr, in

  ///                  which case it assumed that the statement has been

  ///                  removed, which is only possible if no instruction in it

  ///                  had side-effects or computes a value used by another

  ///                  statement.

  /// @param UserScope Loop scope in which the value is used. Needed to

  ///                  determine whether the value is synthesizable.

  /// @param Val       The value being used.

  /// @param Virtual   Whether to use (and prioritize over instruction location)

  ///                  information about MemoryAccesses.

  ///

  /// @return A VirtualUse object that gives information about @p Val's use in

  ///         @p UserStmt.

  static VirtualUse create(Scop *S, ScopStmt *UserStmt, Loop *UserScope,

                           Value *Val, bool Virtual);

  static VirtualUse create(ScopStmt *UserStmt, Loop *UserScope, Value *Val,

                           bool Virtual) {

    return create(UserStmt->getParent(), UserStmt, UserScope, Val, Virtual);

  }

  bool isConstant() const { return Kind == Constant; }

  bool isBlock() const { return Kind == Block; }

  bool isSynthesizable() const { return Kind == Synthesizable; }

  bool isHoisted() const { return Kind == Hoisted; }

  bool isReadOnly() const { return Kind == ReadOnly; }

  bool isIntra() const { return Kind == Intra; }

  bool isInter() const { return Kind == Inter; }

  /// Return user statement.

  ScopStmt *getUser() const { return User; }

  /// Return the used value.

  llvm::Value *getValue() const { return Val; }

  /// Return the type of use.

  UseKind getKind() const { return Kind; }

  /// Return the ScalarEvolution representation of @p Val.

  const SCEV *getScevExpr() const { return ScevExpr; }

  /// Return the MemoryAccess that makes the value available in this statement,

  /// if any.

  MemoryAccess *getMemoryAccess() const { return InputMA; }

  /// Print a description of this object.

  ///

  /// @param OS           Stream to print to.

  /// @param Reproducible If true, ensures that the output is stable between

  ///                     runs and is suitable to check in regression tests.

  ///                     This excludes printing e.g. pointer values. If false,

  ///                     the output should not be used for regression tests,

  ///                     but may contain more information useful in debugger

  ///                     sessions.

  void print(raw_ostream &OS, bool Reproducible = true) const;

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)

  void dump() const;

#endif

};

/// An iterator for virtual operands.

class VirtualOperandIterator final {

  friend class VirtualInstruction;

  friend class VirtualUse;

  using Self = VirtualOperandIterator;

  ScopStmt *User;

  User::op_iterator U;

  VirtualOperandIterator(ScopStmt *User, User::op_iterator U)

      : User(User), U(U) {}

public:

  using iterator_category = std::forward_iterator_tag;

  using value_type = VirtualUse;

  using difference_type = std::ptrdiff_t;

  using pointer = value_type *;

  using reference = value_type &;

  inline bool operator==(const Self &that) const {

    assert(this->User == that.User);

    return this->U == that.U;

  }

  inline bool operator!=(const Self &that) const {

    assert(this->User == that.User);

    return this->U != that.U;

  }

  VirtualUse operator*() const {

    return VirtualUse::create(User, User->getSurroundingLoop(), U->get(), true);

  }

  Use *operator->() const { return U; }

  Self &operator++() {

    U++;

    return *this;

  }

  Self operator++(int) {

    Self tmp = *this;

    ++*this;

    return tmp;

  }

};

/// This class represents a "virtual instruction", an instruction in a ScopStmt,

/// effectively a ScopStmt/Instruction-pair.

///

/// An instructions can be moved between statements (e.g. to avoid a scalar

/// dependency) and even can be contained in multiple statements (for instance,

/// to recompute a value instead of transferring it), hence 'virtual'. This

/// class is required to represent such instructions that are not in their

/// 'physical' location anymore.

///

/// A statement can currently not contain the same instructions multiple times

/// (that is, from different loop iterations). Therefore, a

/// ScopStmt/Instruction-pair uniquely identifies a virtual instructions.

/// ScopStmt::getInstruction() can contain the same instruction multiple times,

/// but they necessarily compute the same value.

class VirtualInstruction final {

  friend class VirtualOperandIterator;

  friend struct llvm::DenseMapInfo<VirtualInstruction>;

private:

  /// The statement this virtual instruction is in.

  ScopStmt *Stmt = nullptr;

  /// The instruction of a statement.

  Instruction *Inst = nullptr;

public:

  VirtualInstruction() {}

  /// Create a new virtual instruction of an instruction @p Inst in @p Stmt.

  VirtualInstruction(ScopStmt *Stmt, Instruction *Inst)

      : Stmt(Stmt), Inst(Inst) {

    assert(Stmt && Inst);

  }

  VirtualOperandIterator operand_begin() const {

    return VirtualOperandIterator(Stmt, Inst->op_begin());

  }

  VirtualOperandIterator operand_end() const {

    return VirtualOperandIterator(Stmt, Inst->op_end());

  }

  /// Returns a list of virtual operands.

  ///

  /// Virtual operands, like virtual instructions, need to encode the ScopStmt

  /// they are in.

  llvm::iterator_range<VirtualOperandIterator> operands() const {

    return {operand_begin(), operand_end()};

  }

  /// Return the SCoP everything is contained in.

  Scop *getScop() const { return Stmt->getParent(); }

  /// Return the ScopStmt this virtual instruction is in.

  ScopStmt *getStmt() const { return Stmt; }

  /// Return the instruction in the statement.

  Instruction *getInstruction() const { return Inst; }

  /// Print a description of this object.

  ///

  /// @param OS           Stream to print to.

  /// @param Reproducible If true, ensures that the output is stable between

  ///                     runs and is suitable for checks in regression tests.

  ///                     This excludes printing e.g., pointer values. If false,

  ///                     the output should not be used for regression tests,

  ///                     but may contain more information useful in debugger

  ///                     sessions.

  void print(raw_ostream &OS, bool Reproducible = true) const;

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)

  void dump() const;

#endif

};

static inline bool operator==(VirtualInstruction LHS, VirtualInstruction RHS) {

  return LHS.getStmt() == RHS.getStmt() &&

         LHS.getInstruction() == RHS.getInstruction();

}

/// Find all reachable instructions and accesses.

///

/// @param S              The SCoP to find everything reachable in.

/// @param LI             LoopInfo required for analysis.

/// @param UsedInsts[out] Receives all reachable instructions.

/// @param UsedAccs[out]  Receives all reachable accesses.

/// @param OnlyLocal      If non-nullptr, activates local mode: The SCoP is

///                       assumed to consist only of this statement and is

///                       conservatively correct. Does not require walking the

///                       whole SCoP.

void markReachable(Scop *S, LoopInfo *LI,

                   DenseSet<VirtualInstruction> &UsedInsts,

                   DenseSet<MemoryAccess *> &UsedAccs,

                   ScopStmt *OnlyLocal = nullptr);

} // namespace polly

namespace llvm {

/// Support VirtualInstructions in llvm::DenseMaps.

template <> struct DenseMapInfo<polly::VirtualInstruction> {

public:

  static bool isEqual(polly::VirtualInstruction LHS,

                      polly::VirtualInstruction RHS) {

    return DenseMapInfo<polly::ScopStmt *>::isEqual(LHS.getStmt(),

                                                    RHS.getStmt()) &&

           DenseMapInfo<Instruction *>::isEqual(LHS.getInstruction(),

                                                RHS.getInstruction());

  }

  static polly::VirtualInstruction getTombstoneKey() {

    polly::VirtualInstruction TombstoneKey;

    TombstoneKey.Stmt = DenseMapInfo<polly::ScopStmt *>::getTombstoneKey();

    TombstoneKey.Inst = DenseMapInfo<Instruction *>::getTombstoneKey();

    return TombstoneKey;

  }

  static polly::VirtualInstruction getEmptyKey() {

    polly::VirtualInstruction EmptyKey;

    EmptyKey.Stmt = DenseMapInfo<polly::ScopStmt *>::getEmptyKey();

    EmptyKey.Inst = DenseMapInfo<Instruction *>::getEmptyKey();

    return EmptyKey;

  }

  static unsigned getHashValue(polly::VirtualInstruction Val) {

    return DenseMapInfo<std::pair<polly::ScopStmt *, Instruction *>>::

        getHashValue(std::make_pair(Val.getStmt(), Val.getInstruction()));

  }

};

} // namespace llvm

#endif /* POLLY_SUPPORT_VIRTUALINSTRUCTION_H */