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 alignment. |
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 | LLVM_PREFERRED_TYPE(bool) |
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. |
82 | CharUnits StorageOffset; |
83 | |
84 | /// The offset within a contiguous run of bitfields that are represented as a |
85 | /// single "field" within the LLVM struct type, taking into account the AAPCS |
86 | /// rules for volatile bitfields. This offset is in bits. |
87 | unsigned VolatileOffset : 16; |
88 | |
89 | /// The storage size in bits which should be used when accessing this |
90 | /// bitfield. |
91 | unsigned VolatileStorageSize; |
92 | |
93 | /// The offset of the bitfield storage from the start of the struct. |
94 | CharUnits VolatileStorageOffset; |
95 | |
96 | CGBitFieldInfo() |
97 | : Offset(), Size(), IsSigned(), StorageSize(), VolatileOffset(), |
98 | VolatileStorageSize() {} |
99 | |
100 | CGBitFieldInfo(unsigned Offset, unsigned Size, bool IsSigned, |
101 | unsigned StorageSize, CharUnits StorageOffset) |
102 | : Offset(Offset), Size(Size), IsSigned(IsSigned), |
103 | StorageSize(StorageSize), StorageOffset(StorageOffset) {} |
104 | |
105 | void print(raw_ostream &OS) const; |
106 | void dump() const; |
107 | |
108 | /// Given a bit-field decl, build an appropriate helper object for |
109 | /// accessing that field (which is expected to have the given offset and |
110 | /// size). |
111 | static CGBitFieldInfo MakeInfo(class CodeGenTypes &Types, |
112 | const FieldDecl *FD, |
113 | uint64_t Offset, uint64_t Size, |
114 | uint64_t StorageSize, |
115 | CharUnits StorageOffset); |
116 | }; |
117 | |
118 | /// CGRecordLayout - This class handles struct and union layout info while |
119 | /// lowering AST types to LLVM types. |
120 | /// |
121 | /// These layout objects are only created on demand as IR generation requires. |
122 | class CGRecordLayout { |
123 | friend class CodeGenTypes; |
124 | |
125 | CGRecordLayout(const CGRecordLayout &) = delete; |
126 | void operator=(const CGRecordLayout &) = delete; |
127 | |
128 | private: |
129 | /// The LLVM type corresponding to this record layout; used when |
130 | /// laying it out as a complete object. |
131 | llvm::StructType *CompleteObjectType; |
132 | |
133 | /// The LLVM type for the non-virtual part of this record layout; |
134 | /// used when laying it out as a base subobject. |
135 | llvm::StructType *BaseSubobjectType; |
136 | |
137 | /// Map from (non-bit-field) struct field to the corresponding llvm struct |
138 | /// type field no. This info is populated by record builder. |
139 | llvm::DenseMap<const FieldDecl *, unsigned> FieldInfo; |
140 | |
141 | /// Map from (bit-field) struct field to the corresponding llvm struct type |
142 | /// field no. This info is populated by record builder. |
143 | llvm::DenseMap<const FieldDecl *, CGBitFieldInfo> BitFields; |
144 | |
145 | // FIXME: Maybe we could use a CXXBaseSpecifier as the key and use a single |
146 | // map for both virtual and non-virtual bases. |
147 | llvm::DenseMap<const CXXRecordDecl *, unsigned> NonVirtualBases; |
148 | |
149 | /// Map from virtual bases to their field index in the complete object. |
150 | llvm::DenseMap<const CXXRecordDecl *, unsigned> CompleteObjectVirtualBases; |
151 | |
152 | /// False if any direct or indirect subobject of this class, when |
153 | /// considered as a complete object, requires a non-zero bitpattern |
154 | /// when zero-initialized. |
155 | bool IsZeroInitializable : 1; |
156 | |
157 | /// False if any direct or indirect subobject of this class, when |
158 | /// considered as a base subobject, requires a non-zero bitpattern |
159 | /// when zero-initialized. |
160 | bool IsZeroInitializableAsBase : 1; |
161 | |
162 | public: |
163 | CGRecordLayout(llvm::StructType *CompleteObjectType, |
164 | llvm::StructType *BaseSubobjectType, |
165 | bool IsZeroInitializable, |
166 | bool IsZeroInitializableAsBase) |
167 | : CompleteObjectType(CompleteObjectType), |
168 | BaseSubobjectType(BaseSubobjectType), |
169 | IsZeroInitializable(IsZeroInitializable), |
170 | IsZeroInitializableAsBase(IsZeroInitializableAsBase) {} |
171 | |
172 | /// Return the "complete object" LLVM type associated with |
173 | /// this record. |
174 | llvm::StructType *getLLVMType() const { |
175 | return CompleteObjectType; |
176 | } |
177 | |
178 | /// Return the "base subobject" LLVM type associated with |
179 | /// this record. |
180 | llvm::StructType *getBaseSubobjectLLVMType() const { |
181 | return BaseSubobjectType; |
182 | } |
183 | |
184 | /// Check whether this struct can be C++ zero-initialized |
185 | /// with a zeroinitializer. |
186 | bool isZeroInitializable() const { |
187 | return IsZeroInitializable; |
188 | } |
189 | |
190 | /// Check whether this struct can be C++ zero-initialized |
191 | /// with a zeroinitializer when considered as a base subobject. |
192 | bool isZeroInitializableAsBase() const { |
193 | return IsZeroInitializableAsBase; |
194 | } |
195 | |
196 | bool containsFieldDecl(const FieldDecl *FD) const { |
197 | return FieldInfo.count(Val: FD) != 0; |
198 | } |
199 | |
200 | /// Return llvm::StructType element number that corresponds to the |
201 | /// field FD. |
202 | unsigned getLLVMFieldNo(const FieldDecl *FD) const { |
203 | FD = FD->getCanonicalDecl(); |
204 | assert(FieldInfo.count(FD) && "Invalid field for record!" ); |
205 | return FieldInfo.lookup(Val: FD); |
206 | } |
207 | |
208 | // Return whether the following non virtual base has a corresponding |
209 | // entry in the LLVM struct. |
210 | bool hasNonVirtualBaseLLVMField(const CXXRecordDecl *RD) const { |
211 | return NonVirtualBases.count(Val: RD); |
212 | } |
213 | |
214 | unsigned getNonVirtualBaseLLVMFieldNo(const CXXRecordDecl *RD) const { |
215 | assert(NonVirtualBases.count(RD) && "Invalid non-virtual base!" ); |
216 | return NonVirtualBases.lookup(Val: RD); |
217 | } |
218 | |
219 | /// Return the LLVM field index corresponding to the given |
220 | /// virtual base. Only valid when operating on the complete object. |
221 | unsigned getVirtualBaseIndex(const CXXRecordDecl *base) const { |
222 | assert(CompleteObjectVirtualBases.count(base) && "Invalid virtual base!" ); |
223 | return CompleteObjectVirtualBases.lookup(Val: base); |
224 | } |
225 | |
226 | /// Return the BitFieldInfo that corresponds to the field FD. |
227 | const CGBitFieldInfo &getBitFieldInfo(const FieldDecl *FD) const { |
228 | FD = FD->getCanonicalDecl(); |
229 | assert(FD->isBitField() && "Invalid call for non-bit-field decl!" ); |
230 | llvm::DenseMap<const FieldDecl *, CGBitFieldInfo>::const_iterator |
231 | it = BitFields.find(Val: FD); |
232 | assert(it != BitFields.end() && "Unable to find bitfield info" ); |
233 | return it->second; |
234 | } |
235 | |
236 | void print(raw_ostream &OS) const; |
237 | void dump() const; |
238 | }; |
239 | |
240 | } // end namespace CodeGen |
241 | } // end namespace clang |
242 | |
243 | #endif |
244 | |