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//===- 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.
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include <cassert>
#include <cstdint>
#include <iterator>
namespace llvm {
class AsmPrinter;
class APInt;
class ByteStreamer;
class DwarfUnit;
class DIELoc;
class TargetRegisterInfo;
/// Holds a DIExpression and keeps track of how many operands have been consumed
/// so far.
class DIExpressionCursor {
DIExpression::expr_op_iterator Start, End;
DIExpressionCursor(const DIExpression *Expr) {
if (!Expr) {
assert(Start == End);
Start = Expr->expr_op_begin();
End = Expr->expr_op_end();
DIExpressionCursor(ArrayRef<uint64_t> Expr)
: Start(Expr.begin()), End(Expr.end()) {}
DIExpressionCursor(const DIExpressionCursor &) = default;
/// 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; }
DIExpression::expr_op_iterator begin() const { return Start; }
DIExpression::expr_op_iterator end() const { return End; }
/// Retrieve the fragment information, if any.
Optional<DIExpression::FragmentInfo> getFragmentInfo() const {
return DIExpression::getFragmentInfo(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 {
/// Holds information about all subregisters comprising a register location.
struct Register {
int DwarfRegNo;
unsigned Size;
const char *Comment;
/// The register location, if any.
SmallVector<Register, 2> DwarfRegs;
/// Current Fragment Offset in Bits.
uint64_t OffsetInBits = 0;
unsigned DwarfVersion;
/// Sometimes we need to add a DW_OP_bit_piece to describe a subregister.
unsigned SubRegisterSizeInBits = 0;
unsigned SubRegisterOffsetInBits = 0;
/// The kind of location description being produced.
enum { Unknown = 0, Register, Memory, Implicit } LocationKind = Unknown;
/// Push a DW_OP_piece / DW_OP_bit_piece for emitting later, if one is needed
/// to represent a subregister.
void setSubRegisterPiece(unsigned SizeInBits, unsigned OffsetInBits) {
SubRegisterSizeInBits = SizeInBits;
SubRegisterOffsetInBits = OffsetInBits;
/// Add masking operations to stencil out a subregister.
void maskSubRegister();
/// 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;
/// Emit a normalized unsigned constant.
void emitConstu(uint64_t Value);
/// 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 DW_OP_reg operation. Note that this is only legal inside a DWARF
/// register location description.
void addReg(int DwarfReg, const char *Comment = nullptr);
/// Emit a DW_OP_breg operation.
void addBReg(int DwarfReg, int Offset);
/// Emit DW_OP_fbreg <Offset>.
void addFBReg(int Offset);
/// Emit a partial DWARF register operation.
/// \param MachineReg The register number.
/// \param MaxSize If the register must be composed from
/// sub-registers this is an upper bound
/// for how many bits the emitted DW_OP_piece
/// may cover.
/// 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 fragment of a super-register or by piecing together
/// multiple subregisters that alias the register.
/// \return false if no DWARF register exists for MachineReg.
bool addMachineReg(const TargetRegisterInfo &TRI, unsigned MachineReg,
unsigned MaxSize = ~1U);
/// Emit a DW_OP_piece or DW_OP_bit_piece operation for a variable fragment.
/// \param OffsetInBits This is an optional offset into the location that
/// is at the top of the DWARF stack.
void addOpPiece(unsigned SizeInBits, unsigned OffsetInBits = 0);
/// Emit a shift-right dwarf operation.
void addShr(unsigned ShiftBy);
/// Emit a bitwise and dwarf operation.
void addAnd(unsigned Mask);
/// 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 address, 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();
~DwarfExpression() = default;
DwarfExpression(unsigned DwarfVersion) : DwarfVersion(DwarfVersion) {}
/// This needs to be called last to commit any pending changes.
void finalize();
/// 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);
bool isMemoryLocation() const { return LocationKind == Memory; }
bool isUnknownLocation() const { return LocationKind == Unknown; }
/// Lock this down to become a memory location description.
void setMemoryLocationKind() {
assert(LocationKind == Unknown);
LocationKind = Memory;
/// 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 FragmentOffsetInBits If this is one fragment out of a
/// fragmented
/// location, this is the offset of the
/// fragment inside the entire variable.
/// \return false if no DWARF register exists
/// for MachineReg.
bool addMachineRegExpression(const TargetRegisterInfo &TRI,
DIExpressionCursor &Expr, unsigned MachineReg,
unsigned FragmentOffsetInBits = 0);
/// Emit all remaining operations in the DIExpressionCursor.
/// \param FragmentOffsetInBits If this is one fragment out of multiple
/// locations, this is the offset of the
/// fragment inside the entire variable.
void addExpression(DIExpressionCursor &&Expr,
unsigned FragmentOffsetInBits = 0);
/// If applicable, emit an empty DW_OP_piece / DW_OP_bit_piece to advance to
/// the fragment described by \c Expr.
void addFragmentOffset(const DIExpression *Expr);
/// DwarfExpression implementation for .debug_loc entries.
class DebugLocDwarfExpression final : public DwarfExpression {
ByteStreamer &BS;
void emitOp(uint8_t Op, const char *Comment = nullptr) override;
void emitSigned(int64_t Value) override;
void emitUnsigned(uint64_t Value) override;
bool isFrameRegister(const TargetRegisterInfo &TRI,
unsigned MachineReg) override;
DebugLocDwarfExpression(unsigned DwarfVersion, ByteStreamer &BS)
: DwarfExpression(DwarfVersion), BS(BS) {}
/// DwarfExpression implementation for singular DW_AT_location.
class DIEDwarfExpression final : public DwarfExpression {
const AsmPrinter &AP;
DwarfUnit &DU;
void emitOp(uint8_t Op, const char *Comment = nullptr) override;
void emitSigned(int64_t Value) override;
void emitUnsigned(uint64_t Value) override;
bool isFrameRegister(const TargetRegisterInfo &TRI,
unsigned MachineReg) override;
DIEDwarfExpression(const AsmPrinter &AP, DwarfUnit &DU, DIELoc &DIE);
DIELoc *finalize() {
return &DIE;
} // end namespace llvm