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CGRecordLayout.h
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1 //===--- CGRecordLayout.h - LLVM Record Layout Information ------*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #ifndef LLVM_CLANG_LIB_CODEGEN_CGRECORDLAYOUT_H
11 #define LLVM_CLANG_LIB_CODEGEN_CGRECORDLAYOUT_H
12 
13 #include "clang/AST/CharUnits.h"
14 #include "clang/AST/DeclCXX.h"
15 #include "clang/Basic/LLVM.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/IR/DerivedTypes.h"
18 
19 namespace llvm {
20  class StructType;
21 }
22 
23 namespace clang {
24 namespace CodeGen {
25 
26 /// \brief Structure with information about how a bitfield should be accessed.
27 ///
28 /// Often we layout a sequence of bitfields as a contiguous sequence of bits.
29 /// When the AST record layout does this, we represent it in the LLVM IR's type
30 /// as either a sequence of i8 members or a byte array to reserve the number of
31 /// bytes touched without forcing any particular alignment beyond the basic
32 /// character alignment.
33 ///
34 /// Then accessing a particular bitfield involves converting this byte array
35 /// into a single integer of that size (i24 or i40 -- may not be power-of-two
36 /// size), loading it, and shifting and masking to extract the particular
37 /// subsequence of bits which make up that particular bitfield. This structure
38 /// encodes the information used to construct the extraction code sequences.
39 /// The CGRecordLayout also has a field index which encodes which byte-sequence
40 /// this bitfield falls within. Let's assume the following C struct:
41 ///
42 /// struct S {
43 /// char a, b, c;
44 /// unsigned bits : 3;
45 /// unsigned more_bits : 4;
46 /// unsigned still_more_bits : 7;
47 /// };
48 ///
49 /// This will end up as the following LLVM type. The first array is the
50 /// bitfield, and the second is the padding out to a 4-byte alignmnet.
51 ///
52 /// %t = type { i8, i8, i8, i8, i8, [3 x i8] }
53 ///
54 /// When generating code to access more_bits, we'll generate something
55 /// essentially like this:
56 ///
57 /// define i32 @foo(%t* %base) {
58 /// %0 = gep %t* %base, i32 0, i32 3
59 /// %2 = load i8* %1
60 /// %3 = lshr i8 %2, 3
61 /// %4 = and i8 %3, 15
62 /// %5 = zext i8 %4 to i32
63 /// ret i32 %i
64 /// }
65 ///
67  /// The offset within a contiguous run of bitfields that are represented as
68  /// a single "field" within the LLVM struct type. This offset is in bits.
69  unsigned Offset : 16;
70 
71  /// The total size of the bit-field, in bits.
72  unsigned Size : 15;
73 
74  /// Whether the bit-field is signed.
75  unsigned IsSigned : 1;
76 
77  /// The storage size in bits which should be used when accessing this
78  /// bitfield.
79  unsigned StorageSize;
80 
81  /// The offset of the bitfield storage from the start of the struct.
83 
85  : Offset(), Size(), IsSigned(), StorageSize(), StorageOffset() {}
86 
87  CGBitFieldInfo(unsigned Offset, unsigned Size, bool IsSigned,
88  unsigned StorageSize, CharUnits StorageOffset)
89  : Offset(Offset), Size(Size), IsSigned(IsSigned),
90  StorageSize(StorageSize), StorageOffset(StorageOffset) {}
91 
92  void print(raw_ostream &OS) const;
93  void dump() const;
94 
95  /// \brief Given a bit-field decl, build an appropriate helper object for
96  /// accessing that field (which is expected to have the given offset and
97  /// size).
98  static CGBitFieldInfo MakeInfo(class CodeGenTypes &Types,
99  const FieldDecl *FD,
100  uint64_t Offset, uint64_t Size,
101  uint64_t StorageSize,
102  CharUnits StorageOffset);
103 };
104 
105 /// CGRecordLayout - This class handles struct and union layout info while
106 /// lowering AST types to LLVM types.
107 ///
108 /// These layout objects are only created on demand as IR generation requires.
110  friend class CodeGenTypes;
111 
112  CGRecordLayout(const CGRecordLayout &) = delete;
113  void operator=(const CGRecordLayout &) = delete;
114 
115 private:
116  /// The LLVM type corresponding to this record layout; used when
117  /// laying it out as a complete object.
118  llvm::StructType *CompleteObjectType;
119 
120  /// The LLVM type for the non-virtual part of this record layout;
121  /// used when laying it out as a base subobject.
122  llvm::StructType *BaseSubobjectType;
123 
124  /// Map from (non-bit-field) struct field to the corresponding llvm struct
125  /// type field no. This info is populated by record builder.
126  llvm::DenseMap<const FieldDecl *, unsigned> FieldInfo;
127 
128  /// Map from (bit-field) struct field to the corresponding llvm struct type
129  /// field no. This info is populated by record builder.
130  llvm::DenseMap<const FieldDecl *, CGBitFieldInfo> BitFields;
131 
132  // FIXME: Maybe we could use a CXXBaseSpecifier as the key and use a single
133  // map for both virtual and non-virtual bases.
134  llvm::DenseMap<const CXXRecordDecl *, unsigned> NonVirtualBases;
135 
136  /// Map from virtual bases to their field index in the complete object.
137  llvm::DenseMap<const CXXRecordDecl *, unsigned> CompleteObjectVirtualBases;
138 
139  /// False if any direct or indirect subobject of this class, when
140  /// considered as a complete object, requires a non-zero bitpattern
141  /// when zero-initialized.
142  bool IsZeroInitializable : 1;
143 
144  /// False if any direct or indirect subobject of this class, when
145  /// considered as a base subobject, requires a non-zero bitpattern
146  /// when zero-initialized.
147  bool IsZeroInitializableAsBase : 1;
148 
149 public:
150  CGRecordLayout(llvm::StructType *CompleteObjectType,
151  llvm::StructType *BaseSubobjectType,
152  bool IsZeroInitializable,
153  bool IsZeroInitializableAsBase)
154  : CompleteObjectType(CompleteObjectType),
155  BaseSubobjectType(BaseSubobjectType),
156  IsZeroInitializable(IsZeroInitializable),
157  IsZeroInitializableAsBase(IsZeroInitializableAsBase) {}
158 
159  /// \brief Return the "complete object" LLVM type associated with
160  /// this record.
161  llvm::StructType *getLLVMType() const {
162  return CompleteObjectType;
163  }
164 
165  /// \brief Return the "base subobject" LLVM type associated with
166  /// this record.
167  llvm::StructType *getBaseSubobjectLLVMType() const {
168  return BaseSubobjectType;
169  }
170 
171  /// \brief Check whether this struct can be C++ zero-initialized
172  /// with a zeroinitializer.
173  bool isZeroInitializable() const {
174  return IsZeroInitializable;
175  }
176 
177  /// \brief Check whether this struct can be C++ zero-initialized
178  /// with a zeroinitializer when considered as a base subobject.
180  return IsZeroInitializableAsBase;
181  }
182 
183  /// \brief Return llvm::StructType element number that corresponds to the
184  /// field FD.
185  unsigned getLLVMFieldNo(const FieldDecl *FD) const {
186  FD = FD->getCanonicalDecl();
187  assert(FieldInfo.count(FD) && "Invalid field for record!");
188  return FieldInfo.lookup(FD);
189  }
190 
191  unsigned getNonVirtualBaseLLVMFieldNo(const CXXRecordDecl *RD) const {
192  assert(NonVirtualBases.count(RD) && "Invalid non-virtual base!");
193  return NonVirtualBases.lookup(RD);
194  }
195 
196  /// \brief Return the LLVM field index corresponding to the given
197  /// virtual base. Only valid when operating on the complete object.
198  unsigned getVirtualBaseIndex(const CXXRecordDecl *base) const {
199  assert(CompleteObjectVirtualBases.count(base) && "Invalid virtual base!");
200  return CompleteObjectVirtualBases.lookup(base);
201  }
202 
203  /// \brief Return the BitFieldInfo that corresponds to the field FD.
204  const CGBitFieldInfo &getBitFieldInfo(const FieldDecl *FD) const {
205  FD = FD->getCanonicalDecl();
206  assert(FD->isBitField() && "Invalid call for non-bit-field decl!");
207  llvm::DenseMap<const FieldDecl *, CGBitFieldInfo>::const_iterator
208  it = BitFields.find(FD);
209  assert(it != BitFields.end() && "Unable to find bitfield info");
210  return it->second;
211  }
212 
213  void print(raw_ostream &OS) const;
214  void dump() const;
215 };
216 
217 } // end namespace CodeGen
218 } // end namespace clang
219 
220 #endif
const CGBitFieldInfo & getBitFieldInfo(const FieldDecl *FD) const
Return the BitFieldInfo that corresponds to the field FD.
CGRecordLayout - This class handles struct and union layout info while lowering AST types to LLVM typ...
DominatorTree GraphTraits specialization so the DominatorTree can be iterable by generic graph iterat...
Definition: Dominators.h:26
CGBitFieldInfo(unsigned Offset, unsigned Size, bool IsSigned, unsigned StorageSize, CharUnits StorageOffset)
bool isZeroInitializableAsBase() const
Check whether this struct can be C++ zero-initialized with a zeroinitializer when considered as a bas...
FieldDecl * getCanonicalDecl() override
Retrieves the canonical declaration of this field.
Definition: Decl.h:2653
FieldDecl - An instance of this class is created by Sema::ActOnField to represent a member of a struc...
Definition: Decl.h:2461
unsigned getNonVirtualBaseLLVMFieldNo(const CXXRecordDecl *RD) const
unsigned Size
The total size of the bit-field, in bits.
bool isBitField() const
Determines whether this field is a bitfield.
Definition: Decl.h:2539
CharUnits - This is an opaque type for sizes expressed in character units.
Definition: CharUnits.h:38
uint32_t Offset
Definition: CacheTokens.cpp:43
static void dump(llvm::raw_ostream &OS, StringRef FunctionName, ArrayRef< CounterExpression > Expressions, ArrayRef< CounterMappingRegion > Regions)
Forward-declares and imports various common LLVM datatypes that clang wants to use unqualified...
CharUnits StorageOffset
The offset of the bitfield storage from the start of the struct.
llvm::StructType * getBaseSubobjectLLVMType() const
Return the "base subobject" LLVM type associated with this record.
unsigned Offset
The offset within a contiguous run of bitfields that are represented as a single "field" within the L...
bool isZeroInitializable() const
Check whether this struct can be C++ zero-initialized with a zeroinitializer.
CGRecordLayout(llvm::StructType *CompleteObjectType, llvm::StructType *BaseSubobjectType, bool IsZeroInitializable, bool IsZeroInitializableAsBase)
Dataflow Directional Tag Classes.
unsigned IsSigned
Whether the bit-field is signed.
unsigned StorageSize
The storage size in bits which should be used when accessing this bitfield.
This class organizes the cross-module state that is used while lowering AST types to LLVM types...
Definition: CodeGenTypes.h:120
llvm::StructType * getLLVMType() const
Return the "complete object" LLVM type associated with this record.
Defines the C++ Decl subclasses, other than those for templates (found in DeclTemplate.h) and friends (in DeclFriend.h).
Represents a C++ struct/union/class.
Definition: DeclCXX.h:299
unsigned getVirtualBaseIndex(const CXXRecordDecl *base) const
Return the LLVM field index corresponding to the given virtual base.
Structure with information about how a bitfield should be accessed.
unsigned getLLVMFieldNo(const FieldDecl *FD) const
Return llvm::StructType element number that corresponds to the field FD.