1//===--- Descriptor.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 descriptors which characterise allocations.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_CLANG_AST_INTERP_DESCRIPTOR_H
14#define LLVM_CLANG_AST_INTERP_DESCRIPTOR_H
15
16#include "clang/AST/Decl.h"
17#include "clang/AST/Expr.h"
18
19namespace clang {
20namespace interp {
21class Block;
22class Record;
23struct Descriptor;
24enum PrimType : unsigned;
25
26using DeclTy = llvm::PointerUnion<const Decl *, const Expr *>;
27
28/// Invoked whenever a block is created. The constructor method fills in the
29/// inline descriptors of all fields and array elements. It also initializes
30/// all the fields which contain non-trivial types.
31using BlockCtorFn = void (*)(Block *Storage, char *FieldPtr, bool IsConst,
32                             bool IsMutable, bool IsActive,
33                             Descriptor *FieldDesc);
34
35/// Invoked when a block is destroyed. Invokes the destructors of all
36/// non-trivial nested fields of arrays and records.
37using BlockDtorFn = void (*)(Block *Storage, char *FieldPtr,
38                             Descriptor *FieldDesc);
39
40/// Invoked when a block with pointers referencing it goes out of scope. Such
41/// blocks are persisted: the move function copies all inline descriptors and
42/// non-trivial fields, as existing pointers might need to reference those
43/// descriptors. Data is not copied since it cannot be legally read.
44using BlockMoveFn = void (*)(Block *Storage, char *SrcFieldPtr,
45                             char *DstFieldPtr, Descriptor *FieldDesc);
46
47/// Object size as used by the interpreter.
48using InterpSize = unsigned;
49
50/// Describes a memory block created by an allocation site.
51struct Descriptor {
52private:
53  /// Original declaration, used to emit the error message.
54  const DeclTy Source;
55  /// Size of an element, in host bytes.
56  const InterpSize ElemSize;
57  /// Size of the storage, in host bytes.
58  const InterpSize Size;
59  /// Size of the allocation (storage + metadata), in host bytes.
60  const InterpSize AllocSize;
61
62  /// Value to denote arrays of unknown size.
63  static constexpr unsigned UnknownSizeMark = (unsigned)-1;
64
65public:
66  /// Token to denote structures of unknown size.
67  struct UnknownSize {};
68
69  /// Pointer to the record, if block contains records.
70  Record *const ElemRecord = nullptr;
71  /// Descriptor of the array element.
72  Descriptor *const ElemDesc = nullptr;
73  /// Flag indicating if the block is mutable.
74  const bool IsConst = false;
75  /// Flag indicating if a field is mutable.
76  const bool IsMutable = false;
77  /// Flag indicating if the block is a temporary.
78  const bool IsTemporary = false;
79  /// Flag indicating if the block is an array.
80  const bool IsArray = false;
81
82  /// Storage management methods.
83  const BlockCtorFn CtorFn = nullptr;
84  const BlockDtorFn DtorFn = nullptr;
85  const BlockMoveFn MoveFn = nullptr;
86
87  /// Allocates a descriptor for a primitive.
88  Descriptor(const DeclTy &D, PrimType Type, bool IsConst, bool IsTemporary,
89             bool IsMutable);
90
91  /// Allocates a descriptor for an array of primitives.
92  Descriptor(const DeclTy &D, PrimType Type, size_t NumElems, bool IsConst,
93             bool IsTemporary, bool IsMutable);
94
95  /// Allocates a descriptor for an array of primitives of unknown size.
96  Descriptor(const DeclTy &D, PrimType Type, bool IsTemporary, UnknownSize);
97
98  /// Allocates a descriptor for an array of composites.
99  Descriptor(const DeclTy &D, Descriptor *Elem, unsigned NumElems, bool IsConst,
100             bool IsTemporary, bool IsMutable);
101
102  /// Allocates a descriptor for an array of composites of unknown size.
103  Descriptor(const DeclTy &D, Descriptor *Elem, bool IsTemporary, UnknownSize);
104
105  /// Allocates a descriptor for a record.
106  Descriptor(const DeclTy &D, Record *R, bool IsConst, bool IsTemporary,
107             bool IsMutable);
108
109  QualType getType() const;
110  SourceLocation getLocation() const;
111
112  const Decl *asDecl() const { return Source.dyn_cast<const Decl *>(); }
113  const Expr *asExpr() const { return Source.dyn_cast<const Expr *>(); }
114
115  const ValueDecl *asValueDecl() const {
116    return dyn_cast_or_null<ValueDecl>(asDecl());
117  }
118
119  const FieldDecl *asFieldDecl() const {
120    return dyn_cast_or_null<FieldDecl>(asDecl());
121  }
122
123  const RecordDecl *asRecordDecl() const {
124    return dyn_cast_or_null<RecordDecl>(asDecl());
125  }
126
127  /// Returns the size of the object without metadata.
128  unsigned getSize() const {
129    assert(!isUnknownSizeArray() && "Array of unknown size");
130    return Size;
131  }
132
133  /// Returns the allocated size, including metadata.
134  unsigned getAllocSize() const { return AllocSize; }
135  /// returns the size of an element when the structure is viewed as an array.
136  unsigned getElemSize()  const { return ElemSize; }
137
138  /// Returns the number of elements stored in the block.
139  unsigned getNumElems() const {
140    return Size == UnknownSizeMark ? 0 : (getSize() / getElemSize());
141  }
142
143  /// Checks if the descriptor is of an array of primitives.
144  bool isPrimitiveArray() const { return IsArray && !ElemDesc; }
145  /// Checks if the descriptor is of an array of zero size.
146  bool isZeroSizeArray() const { return Size == 0; }
147  /// Checks if the descriptor is of an array of unknown size.
148  bool isUnknownSizeArray() const { return Size == UnknownSizeMark; }
149
150  /// Checks if the descriptor is of a primitive.
151  bool isPrimitive() const { return !IsArray && !ElemRecord; }
152
153  /// Checks if the descriptor is of an array.
154  bool isArray() const { return IsArray; }
155};
156
157/// Inline descriptor embedded in structures and arrays.
158///
159/// Such descriptors precede all composite array elements and structure fields.
160/// If the base of a pointer is not zero, the base points to the end of this
161/// structure. The offset field is used to traverse the pointer chain up
162/// to the root structure which allocated the object.
163struct InlineDescriptor {
164  /// Offset inside the structure/array.
165  unsigned Offset;
166
167  /// Flag indicating if the storage is constant or not.
168  /// Relevant for primitive fields.
169  unsigned IsConst : 1;
170  /// For primitive fields, it indicates if the field was initialized.
171  /// Primitive fields in static storage are always initialized.
172  /// Arrays are always initialized, even though their elements might not be.
173  /// Base classes are initialized after the constructor is invoked.
174  unsigned IsInitialized : 1;
175  /// Flag indicating if the field is an embedded base class.
176  unsigned IsBase : 1;
177  /// Flag indicating if the field is the active member of a union.
178  unsigned IsActive : 1;
179  /// Flag indicating if the field is mutable (if in a record).
180  unsigned IsMutable : 1;
181
182  Descriptor *Desc;
183};
184
185/// Bitfield tracking the initialisation status of elements of primitive arrays.
186/// A pointer to this is embedded at the end of all primitive arrays.
187/// If the map was not yet created and nothing was initialied, the pointer to
188/// this structure is 0. If the object was fully initialized, the pointer is -1.
189struct InitMap {
190private:
191  /// Type packing bits.
192  using T = uint64_t;
193  /// Bits stored in a single field.
194  static constexpr uint64_t PER_FIELD = sizeof(T) * CHAR_BIT;
195
196  /// Initializes the map with no fields set.
197  InitMap(unsigned N);
198
199  /// Returns a pointer to storage.
200  T *data();
201
202public:
203  /// Initializes an element. Returns true when object if fully initialized.
204  bool initialize(unsigned I);
205
206  /// Checks if an element was initialized.
207  bool isInitialized(unsigned I);
208
209  /// Allocates a map holding N elements.
210  static InitMap *allocate(unsigned N);
211
212private:
213  /// Number of fields initialized.
214  unsigned UninitFields;
215};
216
217} // namespace interp
218} // namespace clang
219
220#endif
221