clang 10.0.0git

CGRecordLayout.h
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1 //===--- CGRecordLayout.h - LLVM Record Layout Information ------*- 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 #ifndef LLVM_CLANG_LIB_CODEGEN_CGRECORDLAYOUT_H
10 #define LLVM_CLANG_LIB_CODEGEN_CGRECORDLAYOUT_H
11
12 #include "clang/AST/CharUnits.h"
13 #include "clang/AST/DeclCXX.h"
14 #include "clang/Basic/LLVM.h"
15 #include "llvm/ADT/DenseMap.h"
16 #include "llvm/IR/DerivedTypes.h"
17
18 namespace llvm {
19 class StructType;
20 }
21
22 namespace clang {
23 namespace CodeGen {
24
25 /// Structure with information about how a bitfield should be accessed.
26 ///
27 /// Often we layout a sequence of bitfields as a contiguous sequence of bits.
28 /// When the AST record layout does this, we represent it in the LLVM IR's type
29 /// as either a sequence of i8 members or a byte array to reserve the number of
30 /// bytes touched without forcing any particular alignment beyond the basic
31 /// character alignment.
32 ///
33 /// Then accessing a particular bitfield involves converting this byte array
34 /// into a single integer of that size (i24 or i40 -- may not be power-of-two
35 /// size), loading it, and shifting and masking to extract the particular
36 /// subsequence of bits which make up that particular bitfield. This structure
37 /// encodes the information used to construct the extraction code sequences.
38 /// The CGRecordLayout also has a field index which encodes which byte-sequence
39 /// this bitfield falls within. Let's assume the following C struct:
40 ///
41 /// struct S {
42 /// char a, b, c;
43 /// unsigned bits : 3;
44 /// unsigned more_bits : 4;
45 /// unsigned still_more_bits : 7;
46 /// };
47 ///
48 /// This will end up as the following LLVM type. The first array is the
49 /// bitfield, and the second is the padding out to a 4-byte alignmnet.
50 ///
51 /// %t = type { i8, i8, i8, i8, i8, [3 x i8] }
52 ///
53 /// When generating code to access more_bits, we'll generate something
54 /// essentially like this:
55 ///
56 /// define i32 @foo(%t* %base) {
57 /// %0 = gep %t* %base, i32 0, i32 3
58 /// %2 = load i8* %1
59 /// %3 = lshr i8 %2, 3
60 /// %4 = and i8 %3, 15
61 /// %5 = zext i8 %4 to i32
62 /// ret i32 %i
63 /// }
64 ///
65 struct CGBitFieldInfo {
66 /// The offset within a contiguous run of bitfields that are represented as
67 /// a single "field" within the LLVM struct type. This offset is in bits.
68 unsigned Offset : 16;
69
70 /// The total size of the bit-field, in bits.
71 unsigned Size : 15;
72
73 /// Whether the bit-field is signed.
74 unsigned IsSigned : 1;
75
76 /// The storage size in bits which should be used when accessing this
77 /// bitfield.
78 unsigned StorageSize;
79
80 /// The offset of the bitfield storage from the start of the struct.
81 CharUnits StorageOffset;
82
83 CGBitFieldInfo()
84 : Offset(), Size(), IsSigned(), StorageSize(), StorageOffset() {}
85
86 CGBitFieldInfo(unsigned Offset, unsigned Size, bool IsSigned,
87 unsigned StorageSize, CharUnits StorageOffset)
88 : Offset(Offset), Size(Size), IsSigned(IsSigned),
89 StorageSize(StorageSize), StorageOffset(StorageOffset) {}
90
91 void print(raw_ostream &OS) const;
92 void dump() const;
93
94 /// Given a bit-field decl, build an appropriate helper object for
95 /// accessing that field (which is expected to have the given offset and
96 /// size).
97 static CGBitFieldInfo MakeInfo(class CodeGenTypes &Types,
98 const FieldDecl *FD,
99 uint64_t Offset, uint64_t Size,
100 uint64_t StorageSize,
101 CharUnits StorageOffset);
102 };
103
104 /// CGRecordLayout - This class handles struct and union layout info while
105 /// lowering AST types to LLVM types.
106 ///
107 /// These layout objects are only created on demand as IR generation requires.
108 class CGRecordLayout {
109 friend class CodeGenTypes;
110
111 CGRecordLayout(const CGRecordLayout &) = delete;
112 void operator=(const CGRecordLayout &) = delete;
113
114 private:
115 /// The LLVM type corresponding to this record layout; used when
116 /// laying it out as a complete object.
117 llvm::StructType *CompleteObjectType;
118
119 /// The LLVM type for the non-virtual part of this record layout;
120 /// used when laying it out as a base subobject.
121 llvm::StructType *BaseSubobjectType;
122
123 /// Map from (non-bit-field) struct field to the corresponding llvm struct
124 /// type field no. This info is populated by record builder.
125 llvm::DenseMap<const FieldDecl *, unsigned> FieldInfo;
126
127 /// Map from (bit-field) struct field to the corresponding llvm struct type
128 /// field no. This info is populated by record builder.
129 llvm::DenseMap<const FieldDecl *, CGBitFieldInfo> BitFields;
130
131 // FIXME: Maybe we could use a CXXBaseSpecifier as the key and use a single
132 // map for both virtual and non-virtual bases.
133 llvm::DenseMap<const CXXRecordDecl *, unsigned> NonVirtualBases;
134
135 /// Map from virtual bases to their field index in the complete object.
136 llvm::DenseMap<const CXXRecordDecl *, unsigned> CompleteObjectVirtualBases;
137
138 /// False if any direct or indirect subobject of this class, when
139 /// considered as a complete object, requires a non-zero bitpattern
140 /// when zero-initialized.
141 bool IsZeroInitializable : 1;
142
143 /// False if any direct or indirect subobject of this class, when
144 /// considered as a base subobject, requires a non-zero bitpattern
145 /// when zero-initialized.
146 bool IsZeroInitializableAsBase : 1;
147
148 public:
149 CGRecordLayout(llvm::StructType *CompleteObjectType,
150 llvm::StructType *BaseSubobjectType,
151 bool IsZeroInitializable,
152 bool IsZeroInitializableAsBase)
153 : CompleteObjectType(CompleteObjectType),
154 BaseSubobjectType(BaseSubobjectType),
155 IsZeroInitializable(IsZeroInitializable),
156 IsZeroInitializableAsBase(IsZeroInitializableAsBase) {}
157
158 /// Return the "complete object" LLVM type associated with
159 /// this record.
160 llvm::StructType *getLLVMType() const {
161 return CompleteObjectType;
162 }
163
164 /// Return the "base subobject" LLVM type associated with
165 /// this record.
166 llvm::StructType *getBaseSubobjectLLVMType() const {
167 return BaseSubobjectType;
168 }
169
170 /// Check whether this struct can be C++ zero-initialized
171 /// with a zeroinitializer.
172 bool isZeroInitializable() const {
173 return IsZeroInitializable;
174 }
175
176 /// Check whether this struct can be C++ zero-initialized
177 /// with a zeroinitializer when considered as a base subobject.
178 bool isZeroInitializableAsBase() const {
179 return IsZeroInitializableAsBase;
180 }
181
182 /// Return llvm::StructType element number that corresponds to the
183 /// field FD.
184 unsigned getLLVMFieldNo(const FieldDecl *FD) const {
185 FD = FD->getCanonicalDecl();
186 assert(FieldInfo.count(FD) && "Invalid field for record!");
187 return FieldInfo.lookup(FD);
188 }
189
190 unsigned getNonVirtualBaseLLVMFieldNo(const CXXRecordDecl *RD) const {
191 assert(NonVirtualBases.count(RD) && "Invalid non-virtual base!");
192 return NonVirtualBases.lookup(RD);
193 }
194
195 /// Return the LLVM field index corresponding to the given
196 /// virtual base. Only valid when operating on the complete object.
197 unsigned getVirtualBaseIndex(const CXXRecordDecl *base) const {
198 assert(CompleteObjectVirtualBases.count(base) && "Invalid virtual base!");
199 return CompleteObjectVirtualBases.lookup(base);
200 }
201
202 /// Return the BitFieldInfo that corresponds to the field FD.
203 const CGBitFieldInfo &getBitFieldInfo(const FieldDecl *FD) const {
204 FD = FD->getCanonicalDecl();
205 assert(FD->isBitField() && "Invalid call for non-bit-field decl!");
206 llvm::DenseMap<const FieldDecl *, CGBitFieldInfo>::const_iterator
207 it = BitFields.find(FD);
208 assert(it != BitFields.end() && "Unable to find bitfield info");
209 return it->second;
210 }
211
212 void print(raw_ostream &OS) const;
213 void dump() const;
214 };
215
216 } // end namespace CodeGen
217 } // end namespace clang
218
219 #endif
clang::CodeGen::CGRecordLayout::getBitFieldInfo
const CGBitFieldInfo & getBitFieldInfo(const FieldDecl *FD) const
Return the BitFieldInfo that corresponds to the field FD.
Definition: CGRecordLayout.h:203
clang::CodeGen::CGRecordLayout
CGRecordLayout - This class handles struct and union layout info while lowering AST types to LLVM typ...
Definition: CGRecordLayout.h:108
llvm
Specialize PointerLikeTypeTraits to allow LazyGenerationalUpdatePtr to be placed into a PointerUnion...
Definition: Dominators.h:30
clang::CodeGen::CGBitFieldInfo::CGBitFieldInfo
CGBitFieldInfo(unsigned Offset, unsigned Size, bool IsSigned, unsigned StorageSize, CharUnits StorageOffset)
Definition: CGRecordLayout.h:86
print
void print(llvm::raw_ostream &OS, const Pointer &P, ASTContext &Ctx, QualType Ty)
Definition: InterpFrame.cpp:62
clang::CodeGen::CGRecordLayout::isZeroInitializableAsBase
bool isZeroInitializableAsBase() const
Check whether this struct can be C++ zero-initialized with a zeroinitializer when considered as a bas...
Definition: CGRecordLayout.h:178
clang::FieldDecl::getCanonicalDecl
FieldDecl * getCanonicalDecl() override
Retrieves the canonical declaration of this field.
Definition: Decl.h:2929
clang::CodeGen::CGBitFieldInfo::CGBitFieldInfo
CGBitFieldInfo()
Definition: CGRecordLayout.h:83
clang::FieldDecl
Represents a member of a struct/union/class.
Definition: Decl.h:2729
clang::CodeGen::CGRecordLayout::getNonVirtualBaseLLVMFieldNo
unsigned getNonVirtualBaseLLVMFieldNo(const CXXRecordDecl *RD) const
Definition: CGRecordLayout.h:190
CharUnits.h
clang::CodeGen::CGBitFieldInfo::Size
unsigned Size
The total size of the bit-field, in bits.
Definition: CGRecordLayout.h:71
clang::FieldDecl::isBitField
bool isBitField() const
Determines whether this field is a bitfield.
Definition: Decl.h:2807
clang::CharUnits
CharUnits - This is an opaque type for sizes expressed in character units.
Definition: CharUnits.h:38
dump
static void dump(llvm::raw_ostream &OS, StringRef FunctionName, ArrayRef< CounterExpression > Expressions, ArrayRef< CounterMappingRegion > Regions)
Definition: CoverageMappingGen.cpp:1290
LLVM.h
Forward-declares and imports various common LLVM datatypes that clang wants to use unqualified...
clang::CodeGen::CGBitFieldInfo::StorageOffset
CharUnits StorageOffset
The offset of the bitfield storage from the start of the struct.
Definition: CGRecordLayout.h:81
clang::CodeGen::CGRecordLayout::getBaseSubobjectLLVMType
llvm::StructType * getBaseSubobjectLLVMType() const
Return the "base subobject" LLVM type associated with this record.
Definition: CGRecordLayout.h:166
clang::CodeGen::CGBitFieldInfo::Offset
unsigned Offset
The offset within a contiguous run of bitfields that are represented as a single "field" within the L...
Definition: CGRecordLayout.h:68
clang::CodeGen::CGRecordLayout::isZeroInitializable
bool isZeroInitializable() const
Check whether this struct can be C++ zero-initialized with a zeroinitializer.
Definition: CGRecordLayout.h:172
clang::CodeGen::CGRecordLayout::CGRecordLayout
CGRecordLayout(llvm::StructType *CompleteObjectType, llvm::StructType *BaseSubobjectType, bool IsZeroInitializable, bool IsZeroInitializableAsBase)
Definition: CGRecordLayout.h:149
Offset
unsigned Offset
Definition: Format.cpp:1827
clang
Dataflow Directional Tag Classes.
Definition: CFGReachabilityAnalysis.h:21
clang::CodeGen::CGBitFieldInfo::IsSigned
unsigned IsSigned
Whether the bit-field is signed.
Definition: CGRecordLayout.h:74
clang::CodeGen::CGBitFieldInfo::StorageSize
unsigned StorageSize
The storage size in bits which should be used when accessing this bitfield.
Definition: CGRecordLayout.h:78
clang::CodeGen::CodeGenTypes
This class organizes the cross-module state that is used while lowering AST types to LLVM types...
Definition: CodeGenTypes.h:59
clang::CodeGen::CGRecordLayout::getLLVMType
llvm::StructType * getLLVMType() const
Return the "complete object" LLVM type associated with this record.
Definition: CGRecordLayout.h:160
DeclCXX.h
Defines the C++ Decl subclasses, other than those for templates (found in DeclTemplate.h) and friends (in DeclFriend.h).
clang::CXXRecordDecl
Represents a C++ struct/union/class.
Definition: DeclCXX.h:253
clang::CodeGen::CGRecordLayout::getVirtualBaseIndex
unsigned getVirtualBaseIndex(const CXXRecordDecl *base) const
Return the LLVM field index corresponding to the given virtual base.
Definition: CGRecordLayout.h:197
clang::CodeGen::CGBitFieldInfo
Structure with information about how a bitfield should be accessed.
Definition: CGRecordLayout.h:65
clang::CodeGen::CGRecordLayout::getLLVMFieldNo
unsigned getLLVMFieldNo(const FieldDecl *FD) const
Return llvm::StructType element number that corresponds to the field FD.
Definition: CGRecordLayout.h:184