<commit_before>//===-- llvm/CodeGen/DwarfExpression.h - Dwarf Compile Unit ---*- C++ -*--===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains support for writing dwarf compile unit.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIB_CODEGEN_ASMPRINTER_DWARFEXPRESSION_H
#define LLVM_LIB_CODEGEN_ASMPRINTER_DWARFEXPRESSION_H

#include "llvm/IR/DebugInfo.h"
#include "llvm/Support/DataTypes.h"

namespace llvm {

class AsmPrinter;
class ByteStreamer;
class TargetRegisterInfo;
class DwarfUnit;
class DIELoc;

/// Holds a DIExpression and keeps track of how many operands have been consumed
/// so far.
class DIExpressionCursor {
  DIExpression::expr_op_iterator Start, End;
public:
  DIExpressionCursor(const DIExpression *Expr) {
    if (!Expr) {
      assert(Start == End);
      return;
    }
    Start = Expr->expr_op_begin();
    End = Expr->expr_op_end();
  }

  /// Consume one operation.
  Optional<DIExpression::ExprOperand> take() {
    if (Start == End)
      return None;
    return *(Start++);
  }

  /// Consume N operations.
  void consume(unsigned N) { std::advance(Start, N); }

  /// Return the current operation.
  Optional<DIExpression::ExprOperand> peek() const {
    if (Start == End)
      return None;
    return *(Start);
  }

  /// Return the next operation.
  Optional<DIExpression::ExprOperand> peekNext() const {
    if (Start == End)
      return None;

    auto Next = Start.getNext();
    if (Next == End)
      return None;

    return *Next;
  }
  operator bool() const { return Start != End; }
};

/// Base class containing the logic for constructing DWARF expressions
/// independently of whether they are emitted into a DIE or into a .debug_loc
/// entry.
class DwarfExpression {
protected:
  // Various convenience accessors that extract things out of AsmPrinter.
  unsigned DwarfVersion;

public:
  DwarfExpression(unsigned DwarfVersion) : DwarfVersion(DwarfVersion) {}
  virtual ~DwarfExpression() {}

  /// Output a dwarf operand and an optional assembler comment.
  virtual void EmitOp(uint8_t Op, const char *Comment = nullptr) = 0;
  /// Emit a raw signed value.
  virtual void EmitSigned(int64_t Value) = 0;
  /// Emit a raw unsigned value.
  virtual void EmitUnsigned(uint64_t Value) = 0;
  /// Return whether the given machine register is the frame register in the
  /// current function.
  virtual bool isFrameRegister(const TargetRegisterInfo &TRI, unsigned MachineReg) = 0;

  /// Emit a dwarf register operation.
  void AddReg(int DwarfReg, const char *Comment = nullptr);
  /// Emit an (double-)indirect dwarf register operation.
  void AddRegIndirect(int DwarfReg, int Offset, bool Deref = false);

  /// Emit a dwarf register operation for describing
  /// - a small value occupying only part of a register or
  /// - a register representing only part of a value.
  void AddOpPiece(unsigned SizeInBits, unsigned OffsetInBits = 0);
  /// Emit a shift-right dwarf expression.
  void AddShr(unsigned ShiftBy);
  /// Emit a DW_OP_stack_value, if supported.
  ///
  /// The proper way to describe a constant value is
  /// DW_OP_constu <const>, DW_OP_stack_value.
  /// Unfortunately, DW_OP_stack_value was not available until DWARF-4,
  /// so we will continue to generate DW_OP_constu <const> for DWARF-2
  /// and DWARF-3. Technically, this is incorrect since DW_OP_const <const>
  /// actually describes a value at a constant addess, not a constant value.
  /// However, in the past there was no better way  to describe a constant
  /// value, so the producers and consumers started to rely on heuristics
  /// to disambiguate the value vs. location status of the expression.
  /// See PR21176 for more details.
  void AddStackValue();

  /// Emit an indirect dwarf register operation for the given machine register.
  /// \return false if no DWARF register exists for MachineReg.
  bool AddMachineRegIndirect(const TargetRegisterInfo &TRI, unsigned MachineReg,
                             int Offset = 0);

  /// Emit a partial DWARF register operation.
  /// \param MachineReg        the register
  /// \param PieceSizeInBits   size and
  /// \param PieceOffsetInBits offset of the piece in bits, if this is one
  ///                          piece of an aggregate value.
  ///
  /// If size and offset is zero an operation for the entire
  /// register is emitted: Some targets do not provide a DWARF
  /// register number for every register.  If this is the case, this
  /// function will attempt to emit a DWARF register by emitting a
  /// piece of a super-register or by piecing together multiple
  /// subregisters that alias the register.
  ///
  /// \return false if no DWARF register exists for MachineReg.
  bool AddMachineRegPiece(const TargetRegisterInfo &TRI, unsigned MachineReg,
                          unsigned PieceSizeInBits = 0,
                          unsigned PieceOffsetInBits = 0);

  /// Emit a signed constant.
  void AddSignedConstant(int64_t Value);
  /// Emit an unsigned constant.
  void AddUnsignedConstant(uint64_t Value);
  /// Emit an unsigned constant.
  void AddUnsignedConstant(const APInt &Value);

  /// Emit a machine register location while consuming the prefix of a
  /// DwarfExpression.
  ///
  /// \param PieceOffsetInBits     If this is one piece out of a fragmented
  /// location, this is the offset of the piece inside the entire variable.
  /// \return false if no DWARF register exists for MachineReg.
  bool AddMachineRegExpression(const TargetRegisterInfo &TRI,
                               DIExpressionCursor &Expr, unsigned MachineReg,
                               unsigned PieceOffsetInBits = 0);
  /// Emit all remaining operations in the DIExpressionCursor.
  /// \param PieceOffsetInBits     If this is one piece out of a fragmented
  /// location, this is the offset of the piece inside the entire variable.
  void AddExpression(DIExpressionCursor &&Expr,
                     unsigned PieceOffsetInBits = 0);
};

/// DwarfExpression implementation for .debug_loc entries.
class DebugLocDwarfExpression : public DwarfExpression {
  ByteStreamer &BS;

public:
  DebugLocDwarfExpression(unsigned DwarfVersion, ByteStreamer &BS)
      : DwarfExpression(DwarfVersion), BS(BS) {}

  void EmitOp(uint8_t Op, const char *Comment = nullptr) override;
  void EmitSigned(int64_t Value) override;<commit_msg>Improve and cleanup comments in DwarfExpression.h<commit_after>//===-- llvm/CodeGen/DwarfExpression.h - Dwarf Compile Unit ---*- C++ -*--===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains support for writing dwarf compile unit.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIB_CODEGEN_ASMPRINTER_DWARFEXPRESSION_H
#define LLVM_LIB_CODEGEN_ASMPRINTER_DWARFEXPRESSION_H

#include "llvm/IR/DebugInfo.h"
#include "llvm/Support/DataTypes.h"

namespace llvm {

class AsmPrinter;
class ByteStreamer;
class TargetRegisterInfo;
class DwarfUnit;
class DIELoc;

/// Holds a DIExpression and keeps track of how many operands have been consumed
/// so far.
class DIExpressionCursor {
  DIExpression::expr_op_iterator Start, End;
public:
  DIExpressionCursor(const DIExpression *Expr) {
    if (!Expr) {
      assert(Start == End);
      return;
    }
    Start = Expr->expr_op_begin();
    End = Expr->expr_op_end();
  }

  /// Consume one operation.
  Optional<DIExpression::ExprOperand> take() {
    if (Start == End)
      return None;
    return *(Start++);
  }

  /// Consume N operations.
  void consume(unsigned N) { std::advance(Start, N); }

  /// Return the current operation.
  Optional<DIExpression::ExprOperand> peek() const {
    if (Start == End)
      return None;
    return *(Start);
  }

  /// Return the next operation.
  Optional<DIExpression::ExprOperand> peekNext() const {
    if (Start == End)
      return None;

    auto Next = Start.getNext();
    if (Next == End)
      return None;

    return *Next;
  }
  /// Determine whether there are any operations left in this expression.
  operator bool() const { return Start != End; }
};

/// Base class containing the logic for constructing DWARF expressions
/// independently of whether they are emitted into a DIE or into a .debug_loc
/// entry.
class DwarfExpression {
protected:
  // Various convenience accessors that extract things out of AsmPrinter.
  unsigned DwarfVersion;

public:
  DwarfExpression(unsigned DwarfVersion) : DwarfVersion(DwarfVersion) {}
  virtual ~DwarfExpression() {}

  /// Output a dwarf operand and an optional assembler comment.
  virtual void EmitOp(uint8_t Op, const char *Comment = nullptr) = 0;
  /// Emit a raw signed value.
  virtual void EmitSigned(int64_t Value) = 0;
  /// Emit a raw unsigned value.
  virtual void EmitUnsigned(uint64_t Value) = 0;
  /// Return whether the given machine register is the frame register in the
  /// current function.
  virtual bool isFrameRegister(const TargetRegisterInfo &TRI, unsigned MachineReg) = 0;

  /// Emit a dwarf register operation.
  void AddReg(int DwarfReg, const char *Comment = nullptr);
  /// Emit an (double-)indirect dwarf register operation.
  void AddRegIndirect(int DwarfReg, int Offset, bool Deref = false);

  /// Emit DW_OP_piece operation.
  void AddOpPiece(unsigned SizeInBits, unsigned OffsetInBits = 0);
  /// Emit a shift-right dwarf expression.
  void AddShr(unsigned ShiftBy);
  /// Emit a DW_OP_stack_value, if supported.
  ///
  /// The proper way to describe a constant value is DW_OP_constu <const>,
  /// DW_OP_stack_value.  Unfortunately, DW_OP_stack_value was not available
  /// until DWARF 4, so we will continue to generate DW_OP_constu <const> for
  /// DWARF 2 and DWARF 3. Technically, this is incorrect since DW_OP_const
  /// <const> actually describes a value at a constant addess, not a constant
  /// value.  However, in the past there was no better way to describe a
  /// constant value, so the producers and consumers started to rely on
  /// heuristics to disambiguate the value vs. location status of the
  /// expression.  See PR21176 for more details.
  void AddStackValue();

  /// Emit an indirect dwarf register operation for the given machine register.
  /// \return false if no DWARF register exists for MachineReg.
  bool AddMachineRegIndirect(const TargetRegisterInfo &TRI, unsigned MachineReg,
                             int Offset = 0);

  /// Emit a partial DWARF register operation.
  /// \param MachineReg        the register
  /// \param PieceSizeInBits   size and
  /// \param PieceOffsetInBits offset of the piece in bits, if this is one
  ///                          piece of an aggregate value.
  ///
  /// If size and offset is zero an operation for the entire
  /// register is emitted: Some targets do not provide a DWARF
  /// register number for every register.  If this is the case, this
  /// function will attempt to emit a DWARF register by emitting a
  /// piece of a super-register or by piecing together multiple
  /// subregisters that alias the register.
  ///
  /// \return false if no DWARF register exists for MachineReg.
  bool AddMachineRegPiece(const TargetRegisterInfo &TRI, unsigned MachineReg,
                          unsigned PieceSizeInBits = 0,
                          unsigned PieceOffsetInBits = 0);

  /// Emit a signed constant.
  void AddSignedConstant(int64_t Value);
  /// Emit an unsigned constant.
  void AddUnsignedConstant(uint64_t Value);
  /// Emit an unsigned constant.
  void AddUnsignedConstant(const APInt &Value);

  /// Emit a machine register location. As an optimization this may also consume
  /// the prefix of a DwarfExpression if a more efficient representation for
  /// combining the register location and the first operation exists.
  ///
  /// \param PieceOffsetInBits     If this is one piece out of a fragmented
  /// location, this is the offset of the piece inside the entire variable.
  /// \return false if no DWARF register exists for MachineReg.
  bool AddMachineRegExpression(const TargetRegisterInfo &TRI,
                               DIExpressionCursor &Expr, unsigned MachineReg,
                               unsigned PieceOffsetInBits = 0);
  /// Emit all remaining operations in the DIExpressionCursor.
  /// \param PieceOffsetInBits     If this is one piece out of a fragmented
  /// location, this is the offset of the piece inside the entire variable.
  void AddExpression(DIExpressionCursor &&Expr,
                     unsigned PieceOffsetInBits = 0);
};

/// DwarfExpression implementation for .debug_loc entries.
class DebugLocDwarfExpression : public DwarfExpression {
  ByteStreamer &BS;

public:
  DebugLocDwarfExpression(unsigned DwarfVersion, ByteStreamer &BS)
      : DwarfExpression(DwarfVersion), BS(BS) {}

  void EmitOp(uint8_t Op, const char *Comment = nullptr) override;
  void EmitSigned(int64_t Value) override;
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