LLVM  10.0.0svn
DwarfExpression.h
Go to the documentation of this file.
1 //===- llvm/CodeGen/DwarfExpression.h - Dwarf Compile Unit ------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file contains support for writing dwarf compile unit.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_LIB_CODEGEN_ASMPRINTER_DWARFEXPRESSION_H
14 #define LLVM_LIB_CODEGEN_ASMPRINTER_DWARFEXPRESSION_H
15 
16 #include "llvm/ADT/ArrayRef.h"
17 #include "llvm/ADT/None.h"
18 #include "llvm/ADT/Optional.h"
19 #include "llvm/ADT/SmallVector.h"
21 #include <cassert>
22 #include <cstdint>
23 #include <iterator>
24 
25 namespace llvm {
26 
27 class AsmPrinter;
28 class APInt;
29 class ByteStreamer;
30 class DwarfCompileUnit;
31 class DIELoc;
32 class TargetRegisterInfo;
33 
34 /// Holds a DIExpression and keeps track of how many operands have been consumed
35 /// so far.
38 
39 public:
41  if (!Expr) {
42  assert(Start == End);
43  return;
44  }
45  Start = Expr->expr_op_begin();
46  End = Expr->expr_op_end();
47  }
48 
50  : Start(Expr.begin()), End(Expr.end()) {}
51 
52  DIExpressionCursor(const DIExpressionCursor &) = default;
53 
54  /// Consume one operation.
56  if (Start == End)
57  return None;
58  return *(Start++);
59  }
60 
61  /// Consume N operations.
62  void consume(unsigned N) { std::advance(Start, N); }
63 
64  /// Return the current operation.
66  if (Start == End)
67  return None;
68  return *(Start);
69  }
70 
71  /// Return the next operation.
73  if (Start == End)
74  return None;
75 
76  auto Next = Start.getNext();
77  if (Next == End)
78  return None;
79 
80  return *Next;
81  }
82 
83  /// Determine whether there are any operations left in this expression.
84  operator bool() const { return Start != End; }
85 
86  DIExpression::expr_op_iterator begin() const { return Start; }
87  DIExpression::expr_op_iterator end() const { return End; }
88 
89  /// Retrieve the fragment information, if any.
91  return DIExpression::getFragmentInfo(Start, End);
92  }
93 };
94 
95 /// Base class containing the logic for constructing DWARF expressions
96 /// independently of whether they are emitted into a DIE or into a .debug_loc
97 /// entry.
99 protected:
100  /// Holds information about all subregisters comprising a register location.
101  struct Register {
103  unsigned Size;
104  const char *Comment;
105  };
106 
108 
109  /// The register location, if any.
111 
112  /// Current Fragment Offset in Bits.
113  uint64_t OffsetInBits = 0;
114 
115  /// Sometimes we need to add a DW_OP_bit_piece to describe a subregister.
116  unsigned SubRegisterSizeInBits : 16;
117  unsigned SubRegisterOffsetInBits : 16;
118 
119  /// The kind of location description being produced.
120  enum { Unknown = 0, Register, Memory, Implicit };
121 
122  /// The flags of location description being produced.
123  enum { EntryValue = 1, CallSiteParamValue };
124 
125  unsigned LocationKind : 3;
126  unsigned LocationFlags : 2;
127  unsigned DwarfVersion : 4;
128 
129 public:
130  bool isUnknownLocation() const {
131  return LocationKind == Unknown;
132  }
133 
134  bool isMemoryLocation() const {
135  return LocationKind == Memory;
136  }
137 
138  bool isRegisterLocation() const {
139  return LocationKind == Register;
140  }
141 
142  bool isImplicitLocation() const {
143  return LocationKind == Implicit;
144  }
145 
146  bool isEntryValue() const {
147  return LocationFlags & EntryValue;
148  }
149 
151  return LocationFlags & CallSiteParamValue;
152  }
153 
155 
156 protected:
157  /// Push a DW_OP_piece / DW_OP_bit_piece for emitting later, if one is needed
158  /// to represent a subregister.
159  void setSubRegisterPiece(unsigned SizeInBits, unsigned OffsetInBits) {
160  assert(SizeInBits < 65536 && OffsetInBits < 65536);
161  SubRegisterSizeInBits = SizeInBits;
162  SubRegisterOffsetInBits = OffsetInBits;
163  }
164 
165  /// Add masking operations to stencil out a subregister.
166  void maskSubRegister();
167 
168  /// Output a dwarf operand and an optional assembler comment.
169  virtual void emitOp(uint8_t Op, const char *Comment = nullptr) = 0;
170 
171  /// Emit a raw signed value.
172  virtual void emitSigned(int64_t Value) = 0;
173 
174  /// Emit a raw unsigned value.
175  virtual void emitUnsigned(uint64_t Value) = 0;
176 
177  virtual void emitData1(uint8_t Value) = 0;
178 
179  virtual void emitBaseTypeRef(uint64_t Idx) = 0;
180 
181  /// Emit a normalized unsigned constant.
182  void emitConstu(uint64_t Value);
183 
184  /// Return whether the given machine register is the frame register in the
185  /// current function.
186  virtual bool isFrameRegister(const TargetRegisterInfo &TRI, unsigned MachineReg) = 0;
187 
188  /// Emit a DW_OP_reg operation. Note that this is only legal inside a DWARF
189  /// register location description.
190  void addReg(int DwarfReg, const char *Comment = nullptr);
191 
192  /// Emit a DW_OP_breg operation.
193  void addBReg(int DwarfReg, int Offset);
194 
195  /// Emit DW_OP_fbreg <Offset>.
196  void addFBReg(int Offset);
197 
198  /// Emit a partial DWARF register operation.
199  ///
200  /// \param MachineReg The register number.
201  /// \param MaxSize If the register must be composed from
202  /// sub-registers this is an upper bound
203  /// for how many bits the emitted DW_OP_piece
204  /// may cover.
205  ///
206  /// If size and offset is zero an operation for the entire register is
207  /// emitted: Some targets do not provide a DWARF register number for every
208  /// register. If this is the case, this function will attempt to emit a DWARF
209  /// register by emitting a fragment of a super-register or by piecing together
210  /// multiple subregisters that alias the register.
211  ///
212  /// \return false if no DWARF register exists for MachineReg.
213  bool addMachineReg(const TargetRegisterInfo &TRI, unsigned MachineReg,
214  unsigned MaxSize = ~1U);
215 
216  /// Emit a DW_OP_piece or DW_OP_bit_piece operation for a variable fragment.
217  /// \param OffsetInBits This is an optional offset into the location that
218  /// is at the top of the DWARF stack.
219  void addOpPiece(unsigned SizeInBits, unsigned OffsetInBits = 0);
220 
221  /// Emit a shift-right dwarf operation.
222  void addShr(unsigned ShiftBy);
223 
224  /// Emit a bitwise and dwarf operation.
225  void addAnd(unsigned Mask);
226 
227  /// Emit a DW_OP_stack_value, if supported.
228  ///
229  /// The proper way to describe a constant value is DW_OP_constu <const>,
230  /// DW_OP_stack_value. Unfortunately, DW_OP_stack_value was not available
231  /// until DWARF 4, so we will continue to generate DW_OP_constu <const> for
232  /// DWARF 2 and DWARF 3. Technically, this is incorrect since DW_OP_const
233  /// <const> actually describes a value at a constant address, not a constant
234  /// value. However, in the past there was no better way to describe a
235  /// constant value, so the producers and consumers started to rely on
236  /// heuristics to disambiguate the value vs. location status of the
237  /// expression. See PR21176 for more details.
238  void addStackValue();
239 
240  ~DwarfExpression() = default;
241 
242 public:
243  DwarfExpression(unsigned DwarfVersion, DwarfCompileUnit &CU)
244  : CU(CU), SubRegisterSizeInBits(0), SubRegisterOffsetInBits(0),
245  LocationKind(Unknown), LocationFlags(Unknown),
246  DwarfVersion(DwarfVersion) {}
247 
248  /// This needs to be called last to commit any pending changes.
249  void finalize();
250 
251  /// Emit a signed constant.
252  void addSignedConstant(int64_t Value);
253 
254  /// Emit an unsigned constant.
255  void addUnsignedConstant(uint64_t Value);
256 
257  /// Emit an unsigned constant.
258  void addUnsignedConstant(const APInt &Value);
259 
260  /// Lock this down to become a memory location description.
262  assert(isUnknownLocation());
263  LocationKind = Memory;
264  }
265 
266  /// Lock this down to become an entry value location.
268  LocationFlags |= EntryValue;
269  }
270 
271  /// Lock this down to become a call site parameter location.
273  LocationFlags |= CallSiteParamValue;
274  }
275 
276  /// Emit a machine register location. As an optimization this may also consume
277  /// the prefix of a DwarfExpression if a more efficient representation for
278  /// combining the register location and the first operation exists.
279  ///
280  /// \param FragmentOffsetInBits If this is one fragment out of a
281  /// fragmented
282  /// location, this is the offset of the
283  /// fragment inside the entire variable.
284  /// \return false if no DWARF register exists
285  /// for MachineReg.
286  bool addMachineRegExpression(const TargetRegisterInfo &TRI,
287  DIExpressionCursor &Expr, unsigned MachineReg,
288  unsigned FragmentOffsetInBits = 0);
289 
290  /// Emit entry value dwarf operation.
291  void addEntryValueExpression(DIExpressionCursor &ExprCursor);
292 
293  /// Emit all remaining operations in the DIExpressionCursor.
294  ///
295  /// \param FragmentOffsetInBits If this is one fragment out of multiple
296  /// locations, this is the offset of the
297  /// fragment inside the entire variable.
298  void addExpression(DIExpressionCursor &&Expr,
299  unsigned FragmentOffsetInBits = 0);
300 
301  /// If applicable, emit an empty DW_OP_piece / DW_OP_bit_piece to advance to
302  /// the fragment described by \c Expr.
303  void addFragmentOffset(const DIExpression *Expr);
304 
305  void emitLegacySExt(unsigned FromBits);
306  void emitLegacyZExt(unsigned FromBits);
307 };
308 
309 /// DwarfExpression implementation for .debug_loc entries.
311  ByteStreamer &BS;
312 
313  void emitOp(uint8_t Op, const char *Comment = nullptr) override;
314  void emitSigned(int64_t Value) override;
315  void emitUnsigned(uint64_t Value) override;
316  void emitData1(uint8_t Value) override;
317  void emitBaseTypeRef(uint64_t Idx) override;
318  bool isFrameRegister(const TargetRegisterInfo &TRI,
319  unsigned MachineReg) override;
320 
321 public:
323  : DwarfExpression(DwarfVersion, CU), BS(BS) {}
324 };
325 
326 /// DwarfExpression implementation for singular DW_AT_location.
327 class DIEDwarfExpression final : public DwarfExpression {
328 const AsmPrinter &AP;
329  DIELoc &DIE;
330 
331  void emitOp(uint8_t Op, const char *Comment = nullptr) override;
332  void emitSigned(int64_t Value) override;
333  void emitUnsigned(uint64_t Value) override;
334  void emitData1(uint8_t Value) override;
335  void emitBaseTypeRef(uint64_t Idx) override;
336  bool isFrameRegister(const TargetRegisterInfo &TRI,
337  unsigned MachineReg) override;
338 public:
340 
343  return &DIE;
344  }
345 };
346 
347 } // end namespace llvm
348 
349 #endif // LLVM_LIB_CODEGEN_ASMPRINTER_DWARFEXPRESSION_H
DIELoc - Represents an expression location.
Definition: DIE.h:891
This class represents lattice values for constants.
Definition: AllocatorList.h:23
arc branch finalize
void setMemoryLocationKind()
Lock this down to become a memory location description.
This class provides various memory handling functions that manipulate MemoryBlock instances...
Definition: Memory.h:53
Base class containing the logic for constructing DWARF expressions independently of whether they are ...
unsigned const TargetRegisterInfo * TRI
DwarfExpression(unsigned DwarfVersion, DwarfCompileUnit &CU)
expr_op_iterator expr_op_begin() const
Visit the elements via ExprOperand wrappers.
void setCallSiteParamValueFlag()
Lock this down to become a call site parameter location.
Holds a DIExpression and keeps track of how many operands have been consumed so far.
DwarfExpression implementation for .debug_loc entries.
void setSubRegisterPiece(unsigned SizeInBits, unsigned OffsetInBits)
Push a DW_OP_piece / DW_OP_bit_piece for emitting later, if one is needed to represent a subregister...
expr_op_iterator expr_op_end() const
Optional< DIExpression::ExprOperand > peek() const
Return the current operation.
bool isImplicitLocation() const
Optional< DIExpression::ExprOperand > peekNext() const
Return the next operation.
Optional< DIExpression::ExprOperand > take()
Consume one operation.
DIExpressionCursor(const DIExpression *Expr)
A structured debug information entry.
Definition: DIE.h:700
void setEntryValueFlag()
Lock this down to become an entry value location.
This class is intended to be used as a driving class for all asm writers.
Definition: AsmPrinter.h:78
Optional< FragmentInfo > getFragmentInfo() const
Retrieve the details of this fragment expression.
bool isMemoryLocation() const
TargetRegisterInfo base class - We assume that the target defines a static array of TargetRegisterDes...
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:837
bool isUnknownLocation() const
Promote Memory to Register
Definition: Mem2Reg.cpp:109
DWARF expression.
Class for arbitrary precision integers.
Definition: APInt.h:69
Optional< DIExpression::FragmentInfo > getFragmentInfo() const
Retrieve the fragment information, if any.
Optional< uint8_t > TagOffset
unsigned SubRegisterSizeInBits
Sometimes we need to add a DW_OP_bit_piece to describe a subregister.
void consume(unsigned N)
Consume N operations.
DIExpression::expr_op_iterator begin() const
void finalize()
This needs to be called last to commit any pending changes.
#define N
DIExpressionCursor(ArrayRef< uint64_t > Expr)
DwarfExpression implementation for singular DW_AT_location.
Holds information about all subregisters comprising a register location.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
LLVM Value Representation.
Definition: Value.h:73
DebugLocDwarfExpression(unsigned DwarfVersion, ByteStreamer &BS, DwarfCompileUnit &CU)
std::underlying_type< E >::type Mask()
Get a bitmask with 1s in all places up to the high-order bit of E&#39;s largest value.
Definition: BitmaskEnum.h:80
expr_op_iterator getNext() const
Get the next iterator.
An iterator for expression operands.
DwarfCompileUnit & CU
SmallVector< Register, 2 > DwarfRegs
The register location, if any.
DIExpression::expr_op_iterator end() const
bool isRegisterLocation() const