MachineConstantPool.h

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//===- CodeGen/MachineConstantPool.h - Abstract Constant Pool ---*- 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
//
//===----------------------------------------------------------------------===//
//
/// @file
/// This file declares the MachineConstantPool class which is an abstract
/// constant pool to keep track of constants referenced by a function.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_MACHINECONSTANTPOOL_H
#define LLVM_CODEGEN_MACHINECONSTANTPOOL_H

#include "llvm/ADT/DenseSet.h"
#include "llvm/MC/SectionKind.h"
#include <climits>
#include <vector>

namespace llvm {

class Constant;
class DataLayout;
class FoldingSetNodeID;
class MachineConstantPool;
class raw_ostream;
class Type;

/// Abstract base class for all machine specific constantpool value subclasses.
///
class MachineConstantPoolValue {
  virtual void anchor();

  Type *Ty;

public:
  explicit MachineConstantPoolValue(Type *ty) : Ty(ty) {}
  virtual ~MachineConstantPoolValue() = default;

  /// getType - get type of this MachineConstantPoolValue.
  ///
  Type *getType() const { return Ty; }

  virtual int getExistingMachineCPValue(MachineConstantPool *CP,
                                        unsigned Alignment) = 0;

  virtual void addSelectionDAGCSEId(FoldingSetNodeID &ID) = 0;

  /// print - Implement operator<<
  virtual void print(raw_ostream &O) const = 0;
};

inline raw_ostream &operator<<(raw_ostream &OS,
                               const MachineConstantPoolValue &V) {
  V.print(OS);
  return OS;
}

/// This class is a data container for one entry in a MachineConstantPool.
/// It contains a pointer to the value and an offset from the start of
/// the constant pool.
/// An entry in a MachineConstantPool
class MachineConstantPoolEntry {
public:
  /// The constant itself.
  union {
    const Constant *ConstVal;
    MachineConstantPoolValue *MachineCPVal;
  } Val;

  /// The required alignment for this entry. The top bit is set when Val is
  /// a target specific MachineConstantPoolValue.
  unsigned Alignment;

  MachineConstantPoolEntry(const Constant *V, unsigned A)
    : Alignment(A) {
    Val.ConstVal = V;
  }

  MachineConstantPoolEntry(MachineConstantPoolValue *V, unsigned A)
      : Alignment(A) {
    Val.MachineCPVal = V;
    Alignment |= 1U << (sizeof(unsigned) * CHAR_BIT - 1);
  }

  /// isMachineConstantPoolEntry - Return true if the MachineConstantPoolEntry
  /// is indeed a target specific constantpool entry, not a wrapper over a
  /// Constant.
  bool isMachineConstantPoolEntry() const {
    return (int)Alignment < 0;
  }

  int getAlignment() const {
    return Alignment & ~(1 << (sizeof(unsigned) * CHAR_BIT - 1));
  }

  Type *getType() const;

  /// This method classifies the entry according to whether or not it may
  /// generate a relocation entry.  This must be conservative, so if it might
  /// codegen to a relocatable entry, it should say so.
  bool needsRelocation() const;

  SectionKind getSectionKind(const DataLayout *DL) const;
};

/// The MachineConstantPool class keeps track of constants referenced by a
/// function which must be spilled to memory.  This is used for constants which
/// are unable to be used directly as operands to instructions, which typically
/// include floating point and large integer constants.
///
/// Instructions reference the address of these constant pool constants through
/// the use of MO_ConstantPoolIndex values.  When emitting assembly or machine
/// code, these virtual address references are converted to refer to the
/// address of the function constant pool values.
/// The machine constant pool.
class MachineConstantPool {
  unsigned PoolAlignment;       ///< The alignment for the pool.
  std::vector<MachineConstantPoolEntry> Constants; ///< The pool of constants.
  /// MachineConstantPoolValues that use an existing MachineConstantPoolEntry.
  DenseSet<MachineConstantPoolValue*> MachineCPVsSharingEntries;
  const DataLayout &DL;

  const DataLayout &getDataLayout() const { return DL; }

public:
  /// The only constructor.
  explicit MachineConstantPool(const DataLayout &DL)
      : PoolAlignment(1), DL(DL) {}
  ~MachineConstantPool();

  /// getConstantPoolAlignment - Return the alignment required by
  /// the whole constant pool, of which the first element must be aligned.
  unsigned getConstantPoolAlignment() const { return PoolAlignment; }

  /// getConstantPoolIndex - Create a new entry in the constant pool or return
  /// an existing one.  User must specify the minimum required alignment for
  /// the object.
  unsigned getConstantPoolIndex(const Constant *C, unsigned Alignment);
  unsigned getConstantPoolIndex(MachineConstantPoolValue *V,
                                unsigned Alignment);

  /// isEmpty - Return true if this constant pool contains no constants.
  bool isEmpty() const { return Constants.empty(); }

  const std::vector<MachineConstantPoolEntry> &getConstants() const {
    return Constants;
  }

  /// print - Used by the MachineFunction printer to print information about
  /// constant pool objects.  Implemented in MachineFunction.cpp
  void print(raw_ostream &OS) const;

  /// dump - Call print(cerr) to be called from the debugger.
  void dump() const;
};

} // end namespace llvm

#endif // LLVM_CODEGEN_MACHINECONSTANTPOOL_H