1//===--- Pointer.h - Types for the constexpr VM -----------------*- 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// Defines the classes responsible for pointer tracking.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_CLANG_AST_INTERP_POINTER_H
14#define LLVM_CLANG_AST_INTERP_POINTER_H
15
16#include "Block.h"
17#include "Descriptor.h"
18#include "clang/AST/Decl.h"
19#include "clang/AST/DeclCXX.h"
20#include "clang/AST/Expr.h"
21#include "clang/AST/ComparisonCategories.h"
22#include "llvm/ADT/PointerUnion.h"
23#include "llvm/Support/raw_ostream.h"
24
25namespace clang {
26namespace interp {
27class Block;
28class DeadBlock;
29class Context;
30class InterpState;
31class Pointer;
32class Function;
33enum PrimType : unsigned;
34
35/// A pointer to a memory block, live or dead.
36///
37/// This object can be allocated into interpreter stack frames. If pointing to
38/// a live block, it is a link in the chain of pointers pointing to the block.
39class Pointer {
40private:
41  static constexpr unsigned PastEndMark = (unsigned)-1;
42  static constexpr unsigned RootPtrMark = (unsigned)-1;
43
44public:
45  Pointer() {}
46  Pointer(Block *B);
47  Pointer(const Pointer &P);
48  Pointer(Pointer &&P);
49  ~Pointer();
50
51  void operator=(const Pointer &P);
52  void operator=(Pointer &&P);
53
54  /// Converts the pointer to an APValue.
55  APValue toAPValue() const;
56
57  /// Offsets a pointer inside an array.
58  Pointer atIndex(unsigned Idx) const {
59    if (Base == RootPtrMark)
60      return Pointer(Pointee, RootPtrMark, getDeclDesc()->getSize());
61    unsigned Off = Idx * elemSize();
62    if (getFieldDesc()->ElemDesc)
63      Off += sizeof(InlineDescriptor);
64    else
65      Off += sizeof(InitMap *);
66    return Pointer(Pointee, Base, Base + Off);
67  }
68
69  /// Creates a pointer to a field.
70  Pointer atField(unsigned Off) const {
71    unsigned Field = Offset + Off;
72    return Pointer(Pointee, Field, Field);
73  }
74
75  /// Restricts the scope of an array element pointer.
76  Pointer narrow() const {
77    // Null pointers cannot be narrowed.
78    if (isZero() || isUnknownSizeArray())
79      return *this;
80
81    // Pointer to an array of base types - enter block.
82    if (Base == RootPtrMark)
83      return Pointer(Pointee, 0, Offset == 0 ? Offset : PastEndMark);
84
85    // Pointer is one past end - magic offset marks that.
86    if (isOnePastEnd())
87      return Pointer(Pointee, Base, PastEndMark);
88
89    // Primitive arrays are a bit special since they do not have inline
90    // descriptors. If Offset != Base, then the pointer already points to
91    // an element and there is nothing to do. Otherwise, the pointer is
92    // adjusted to the first element of the array.
93    if (inPrimitiveArray()) {
94      if (Offset != Base)
95        return *this;
96      return Pointer(Pointee, Base, Offset + sizeof(InitMap *));
97    }
98
99    // Pointer is to a field or array element - enter it.
100    if (Offset != Base)
101      return Pointer(Pointee, Offset, Offset);
102
103    // Enter the first element of an array.
104    if (!getFieldDesc()->isArray())
105      return *this;
106
107    const unsigned NewBase = Base + sizeof(InlineDescriptor);
108    return Pointer(Pointee, NewBase, NewBase);
109  }
110
111  /// Expands a pointer to the containing array, undoing narrowing.
112  Pointer expand() const {
113    if (isElementPastEnd()) {
114      // Revert to an outer one-past-end pointer.
115      unsigned Adjust;
116      if (inPrimitiveArray())
117        Adjust = sizeof(InitMap *);
118      else
119        Adjust = sizeof(InlineDescriptor);
120      return Pointer(Pointee, Base, Base + getSize() + Adjust);
121    }
122
123    // Do not step out of array elements.
124    if (Base != Offset)
125      return *this;
126
127    // If at base, point to an array of base types.
128    if (Base == 0)
129      return Pointer(Pointee, RootPtrMark, 0);
130
131    // Step into the containing array, if inside one.
132    unsigned Next = Base - getInlineDesc()->Offset;
133    Descriptor *Desc = Next == 0 ? getDeclDesc() : getDescriptor(Next)->Desc;
134    if (!Desc->IsArray)
135      return *this;
136    return Pointer(Pointee, Next, Offset);
137  }
138
139  /// Checks if the pointer is null.
140  bool isZero() const { return Pointee == nullptr; }
141  /// Checks if the pointer is live.
142  bool isLive() const { return Pointee && !Pointee->IsDead; }
143  /// Checks if the item is a field in an object.
144  bool isField() const { return Base != 0 && Base != RootPtrMark; }
145
146  /// Accessor for information about the declaration site.
147  Descriptor *getDeclDesc() const { return Pointee->Desc; }
148  SourceLocation getDeclLoc() const { return getDeclDesc()->getLocation(); }
149
150  /// Returns a pointer to the object of which this pointer is a field.
151  Pointer getBase() const {
152    if (Base == RootPtrMark) {
153      assert(Offset == PastEndMark && "cannot get base of a block");
154      return Pointer(Pointee, Base, 0);
155    }
156    assert(Offset == Base && "not an inner field");
157    unsigned NewBase = Base - getInlineDesc()->Offset;
158    return Pointer(Pointee, NewBase, NewBase);
159  }
160  /// Returns the parent array.
161  Pointer getArray() const {
162    if (Base == RootPtrMark) {
163      assert(Offset != 0 && Offset != PastEndMark && "not an array element");
164      return Pointer(Pointee, Base, 0);
165    }
166    assert(Offset != Base && "not an array element");
167    return Pointer(Pointee, Base, Base);
168  }
169
170  /// Accessors for information about the innermost field.
171  Descriptor *getFieldDesc() const {
172    if (Base == 0 || Base == RootPtrMark)
173      return getDeclDesc();
174    return getInlineDesc()->Desc;
175  }
176
177  /// Returns the type of the innermost field.
178  QualType getType() const { return getFieldDesc()->getType(); }
179
180  /// Returns the element size of the innermost field.
181  size_t elemSize() const {
182    if (Base == RootPtrMark)
183      return getDeclDesc()->getSize();
184    return getFieldDesc()->getElemSize();
185  }
186  /// Returns the total size of the innermost field.
187  size_t getSize() const { return getFieldDesc()->getSize(); }
188
189  /// Returns the offset into an array.
190  unsigned getOffset() const {
191    assert(Offset != PastEndMark && "invalid offset");
192    if (Base == RootPtrMark)
193      return Offset;
194
195    unsigned Adjust = 0;
196    if (Offset != Base) {
197      if (getFieldDesc()->ElemDesc)
198        Adjust = sizeof(InlineDescriptor);
199      else
200        Adjust = sizeof(InitMap *);
201    }
202    return Offset - Base - Adjust;
203  }
204
205  /// Checks if the innermost field is an array.
206  bool inArray() const { return getFieldDesc()->IsArray; }
207  /// Checks if the structure is a primitive array.
208  bool inPrimitiveArray() const { return getFieldDesc()->isPrimitiveArray(); }
209  /// Checks if the structure is an array of unknown size.
210  bool isUnknownSizeArray() const {
211    return getFieldDesc()->isUnknownSizeArray();
212  }
213  /// Checks if the pointer points to an array.
214  bool isArrayElement() const { return Base != Offset; }
215  /// Pointer points directly to a block.
216  bool isRoot() const {
217    return (Base == 0 || Base == RootPtrMark) && Offset == 0;
218  }
219
220  /// Returns the record descriptor of a class.
221  Record *getRecord() const { return getFieldDesc()->ElemRecord; }
222  /// Returns the field information.
223  const FieldDecl *getField() const { return getFieldDesc()->asFieldDecl(); }
224
225  /// Checks if the object is a union.
226  bool isUnion() const;
227
228  /// Checks if the storage is extern.
229  bool isExtern() const { return Pointee->isExtern(); }
230  /// Checks if the storage is static.
231  bool isStatic() const { return Pointee->isStatic(); }
232  /// Checks if the storage is temporary.
233  bool isTemporary() const { return Pointee->isTemporary(); }
234  /// Checks if the storage is a static temporary.
235  bool isStaticTemporary() const { return isStatic() && isTemporary(); }
236
237  /// Checks if the field is mutable.
238  bool isMutable() const { return Base != 0 && getInlineDesc()->IsMutable; }
239  /// Checks if an object was initialized.
240  bool isInitialized() const;
241  /// Checks if the object is active.
242  bool isActive() const { return Base == 0 || getInlineDesc()->IsActive; }
243  /// Checks if a structure is a base class.
244  bool isBaseClass() const { return isField() && getInlineDesc()->IsBase; }
245
246  /// Checks if an object or a subfield is mutable.
247  bool isConst() const {
248    return Base == 0 ? getDeclDesc()->IsConst : getInlineDesc()->IsConst;
249  }
250
251  /// Returns the declaration ID.
252  llvm::Optional<unsigned> getDeclID() const { return Pointee->getDeclID(); }
253
254  /// Returns the byte offset from the start.
255  unsigned getByteOffset() const {
256    return Offset;
257  }
258
259  /// Returns the number of elements.
260  unsigned getNumElems() const { return getSize() / elemSize(); }
261
262  /// Returns the index into an array.
263  int64_t getIndex() const {
264    if (isElementPastEnd())
265      return 1;
266    if (auto ElemSize = elemSize())
267      return getOffset() / ElemSize;
268    return 0;
269  }
270
271  /// Checks if the index is one past end.
272  bool isOnePastEnd() const {
273    return isElementPastEnd() || getSize() == getOffset();
274  }
275
276  /// Checks if the pointer is an out-of-bounds element pointer.
277  bool isElementPastEnd() const { return Offset == PastEndMark; }
278
279  /// Dereferences the pointer, if it's live.
280  template <typename T> T &deref() const {
281    assert(isLive() && "Invalid pointer");
282    return *reinterpret_cast<T *>(Pointee->data() + Offset);
283  }
284
285  /// Dereferences a primitive element.
286  template <typename T> T &elem(unsigned I) const {
287    return reinterpret_cast<T *>(Pointee->data())[I];
288  }
289
290  /// Initializes a field.
291  void initialize() const;
292  /// Activats a field.
293  void activate() const;
294  /// Deactivates an entire strurcutre.
295  void deactivate() const;
296
297  /// Checks if two pointers are comparable.
298  static bool hasSameBase(const Pointer &A, const Pointer &B);
299  /// Checks if two pointers can be subtracted.
300  static bool hasSameArray(const Pointer &A, const Pointer &B);
301
302  /// Prints the pointer.
303  void print(llvm::raw_ostream &OS) const {
304    OS << "{" << Base << ", " << Offset << ", ";
305    if (Pointee)
306      OS << Pointee->getSize();
307    else
308      OS << "nullptr";
309    OS << "}";
310  }
311
312private:
313  friend class Block;
314  friend class DeadBlock;
315
316  Pointer(Block *Pointee, unsigned Base, unsigned Offset);
317
318  /// Returns the embedded descriptor preceding a field.
319  InlineDescriptor *getInlineDesc() const { return getDescriptor(Base); }
320
321  /// Returns a descriptor at a given offset.
322  InlineDescriptor *getDescriptor(unsigned Offset) const {
323    assert(Offset != 0 && "Not a nested pointer");
324    return reinterpret_cast<InlineDescriptor *>(Pointee->data() + Offset) - 1;
325  }
326
327  /// Returns a reference to the pointer which stores the initialization map.
328  InitMap *&getInitMap() const {
329    return *reinterpret_cast<InitMap **>(Pointee->data() + Base);
330  }
331
332  /// The block the pointer is pointing to.
333  Block *Pointee = nullptr;
334  /// Start of the current subfield.
335  unsigned Base = 0;
336  /// Offset into the block.
337  unsigned Offset = 0;
338
339  /// Previous link in the pointer chain.
340  Pointer *Prev = nullptr;
341  /// Next link in the pointer chain.
342  Pointer *Next = nullptr;
343};
344
345inline llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const Pointer &P) {
346  P.print(OS);
347  return OS;
348}
349
350} // namespace interp
351} // namespace clang
352
353#endif
354