CGRecordLayoutBuilder.cpp revision 4b5584b38b860e8ecb20420e2fe16d5ed97a68a0 
1//===--- CGRecordLayoutBuilder.cpp - Record builder helper ------*- 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// This is a helper class used to build CGRecordLayout objects and LLVM types.
11//
12//===----------------------------------------------------------------------===//
13
14#include "CGRecordLayoutBuilder.h"
15
16#include "clang/AST/ASTContext.h"
17#include "clang/AST/Attr.h"
18#include "clang/AST/DeclCXX.h"
19#include "clang/AST/Expr.h"
20#include "clang/AST/RecordLayout.h"
21#include "CodeGenTypes.h"
22#include "llvm/DerivedTypes.h"
23#include "llvm/Target/TargetData.h"
24
25
26using namespace clang;
27using namespace CodeGen;
28
29void CGRecordLayoutBuilder::Layout(const RecordDecl *D) {
30  if (D->isUnion()) {
31    LayoutUnion(D);
32    return;
33  }
34
35  if (const PackedAttr* PA = D->getAttr<PackedAttr>())
36    Packed = PA->getAlignment();
37
38  if (LayoutFields(D))
39    return;
40
41  // We weren't able to layout the struct. Try again with a packed struct
42  Packed = true;
43  AlignmentAsLLVMStruct = 1;
44  FieldTypes.clear();
45  FieldInfos.clear();
46  LLVMFields.clear();
47  LLVMBitFields.clear();
48
49  LayoutFields(D);
50}
51
52void CGRecordLayoutBuilder::LayoutBitField(const FieldDecl *D,
53                                           uint64_t FieldOffset) {
54  uint64_t FieldSize =
55    D->getBitWidth()->EvaluateAsInt(Types.getContext()).getZExtValue();
56
57  if (FieldSize == 0)
58    return;
59
60  uint64_t NextFieldOffset = getNextFieldOffsetInBytes() * 8;
61  unsigned NumBytesToAppend;
62
63  if (FieldOffset < NextFieldOffset) {
64    assert(BitsAvailableInLastField && "Bitfield size mismatch!");
65    assert(!FieldInfos.empty() && "Field infos can't be empty!");
66
67    // The bitfield begins in the previous bit-field.
68    NumBytesToAppend =
69      llvm::RoundUpToAlignment(FieldSize - BitsAvailableInLastField, 8) / 8;
70  } else {
71    assert(FieldOffset % 8 == 0 && "Field offset not aligned correctly");
72
73    // Append padding if necessary.
74    AppendBytes((FieldOffset - NextFieldOffset) / 8);
75
76    NumBytesToAppend =
77      llvm::RoundUpToAlignment(FieldSize, 8) / 8;
78
79    assert(NumBytesToAppend && "No bytes to append!");
80  }
81
82  const llvm::Type *Ty = Types.ConvertTypeForMemRecursive(D->getType());
83  uint64_t TypeSizeInBits = getTypeSizeInBytes(Ty) * 8;
84
85  LLVMBitFields.push_back(LLVMBitFieldInfo(D, FieldOffset / TypeSizeInBits,
86                                           FieldOffset % TypeSizeInBits,
87                                           FieldSize));
88
89  AppendBytes(NumBytesToAppend);
90
91  if (!NumBytesToAppend)
92    BitsAvailableInLastField -= FieldSize;
93  else
94    BitsAvailableInLastField = NumBytesToAppend * 8 - FieldSize;
95}
96
97bool CGRecordLayoutBuilder::LayoutField(const FieldDecl *D,
98                                        uint64_t FieldOffset) {
99  bool FieldPacked = Packed;
100
101  // FIXME: Should this override struct packing? Probably we want to
102  // take the minimum?
103  if (const PackedAttr *PA = D->getAttr<PackedAttr>())
104    FieldPacked = PA->getAlignment();
105
106  // If the field is packed, then we need a packed struct.
107  if (!Packed && FieldPacked)
108    return false;
109
110  if (D->isBitField()) {
111    // We must use packed structs for unnamed bit fields since they
112    // don't affect the struct alignment.
113    if (!Packed && !D->getDeclName())
114      return false;
115
116    LayoutBitField(D, FieldOffset);
117    return true;
118  }
119
120  const llvm::Type *Ty = Types.ConvertTypeForMemRecursive(D->getType());
121
122  // Check if the field is aligned.
123  if (const AlignedAttr *PA = D->getAttr<AlignedAttr>()) {
124    unsigned FieldAlign = PA->getAlignment();
125
126    if (!Packed && getTypeAlignment(Ty) > FieldAlign)
127      return false;
128  }
129
130  assert(FieldOffset % 8 == 0 && "FieldOffset is not on a byte boundary!");
131
132  uint64_t FieldOffsetInBytes = FieldOffset / 8;
133
134  // Append padding if necessary.
135  AppendPadding(FieldOffsetInBytes, Ty);
136
137  uint64_t FieldSizeInBytes = getTypeSizeInBytes(Ty);
138
139  // Now append the field.
140  LLVMFields.push_back(LLVMFieldInfo(D, FieldTypes.size()));
141  AppendField(FieldOffsetInBytes, FieldSizeInBytes, Ty);
142
143  return true;
144}
145
146void CGRecordLayoutBuilder::LayoutUnion(const RecordDecl *D) {
147  assert(D->isUnion() && "Can't call LayoutUnion on a non-union record!");
148
149  const ASTRecordLayout &Layout = Types.getContext().getASTRecordLayout(D);
150
151  const FieldDecl *FD = 0;
152  const llvm::Type *Ty = 0;
153  uint64_t Size = 0;
154  unsigned Align = 0;
155
156  unsigned FieldNo = 0;
157  for (RecordDecl::field_iterator Field = D->field_begin(),
158       FieldEnd = D->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
159    assert(Layout.getFieldOffset(FieldNo) == 0 &&
160          "Union field offset did not start at the beginning of record!");
161
162    if (Field->isBitField()) {
163      uint64_t FieldSize =
164        Field->getBitWidth()->EvaluateAsInt(Types.getContext()).getZExtValue();
165
166      // Ignore zero sized bit fields.
167      if (FieldSize == 0)
168        continue;
169    }
170
171    const llvm::Type *FieldTy =
172      Types.ConvertTypeForMemRecursive(Field->getType());
173    unsigned FieldAlign = Types.getTargetData().getTypeAllocSize(FieldTy);
174    uint64_t FieldSize = Types.getTargetData().getABITypeAlignment(FieldTy);
175
176    if (FieldAlign < Align)
177      continue;
178
179    if (FieldAlign > Align || FieldSize > Size) {
180      Ty = FieldTy;
181      Align = FieldAlign;
182      Size = FieldSize;
183      FD = *Field;
184    }
185  }
186
187  // Now add our field.
188  if (FD) {
189    AppendField(0, Size, Ty);
190
191    if (FD->isBitField()) {
192      uint64_t FieldSize =
193        FD->getBitWidth()->EvaluateAsInt(Types.getContext()).getZExtValue();
194      Types.addBitFieldInfo(FD, 0, 0, FieldSize);
195    } else
196      Types.addFieldInfo(FD, 0);
197  }
198
199  // Append tail padding.
200  if (Layout.getSize() / 8 > Size)
201    AppendPadding(Layout.getSize() / 8, Align);
202}
203
204bool CGRecordLayoutBuilder::LayoutFields(const RecordDecl *D) {
205  assert(!D->isUnion() && "Can't call LayoutFields on a union!");
206
207  const ASTRecordLayout &Layout = Types.getContext().getASTRecordLayout(D);
208
209  unsigned FieldNo = 0;
210  for (RecordDecl::field_iterator Field = D->field_begin(),
211       FieldEnd = D->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
212    if (!LayoutField(*Field, Layout.getFieldOffset(FieldNo))) {
213      assert(!Packed &&
214             "Could not layout fields even with a packed LLVM struct!");
215      return false;
216    }
217  }
218
219  // Append tail padding if necessary.
220  if (Layout.getSize() / 8 > getNextFieldOffsetInBytes())
221    AppendPadding(Layout.getSize() / 8, AlignmentAsLLVMStruct);
222
223  return true;
224}
225
226void CGRecordLayoutBuilder::AppendField(uint64_t FieldOffsetInBytes,
227                                        uint64_t FieldSizeInBytes,
228                                        const llvm::Type *FieldTy) {
229  AlignmentAsLLVMStruct = std::max(AlignmentAsLLVMStruct,
230                                   getTypeAlignment(FieldTy));
231
232  FieldTypes.push_back(FieldTy);
233  FieldInfos.push_back(FieldInfo(FieldOffsetInBytes, FieldSizeInBytes));
234
235  BitsAvailableInLastField = 0;
236}
237
238void
239CGRecordLayoutBuilder::AppendPadding(uint64_t FieldOffsetInBytes,
240                                     const llvm::Type *FieldTy) {
241  AppendPadding(FieldOffsetInBytes, getTypeAlignment(FieldTy));
242}
243
244void CGRecordLayoutBuilder::AppendPadding(uint64_t FieldOffsetInBytes,
245                                          unsigned FieldAlignment) {
246  uint64_t NextFieldOffsetInBytes = getNextFieldOffsetInBytes();
247  assert(NextFieldOffsetInBytes <= FieldOffsetInBytes &&
248         "Incorrect field layout!");
249
250  // Round up the field offset to the alignment of the field type.
251  uint64_t AlignedNextFieldOffsetInBytes =
252    llvm::RoundUpToAlignment(NextFieldOffsetInBytes, FieldAlignment);
253
254  if (AlignedNextFieldOffsetInBytes < FieldOffsetInBytes) {
255    // Even with alignment, the field offset is not at the right place,
256    // insert padding.
257    uint64_t PaddingInBytes = FieldOffsetInBytes - NextFieldOffsetInBytes;
258
259    AppendBytes(PaddingInBytes);
260  }
261}
262
263void CGRecordLayoutBuilder::AppendBytes(uint64_t NumBytes) {
264  if (NumBytes == 0)
265    return;
266
267  const llvm::Type *Ty = llvm::Type::Int8Ty;
268  if (NumBytes > 1) {
269    // FIXME: Use a VMContext.
270    Ty = llvm::ArrayType::get(Ty, NumBytes);
271  }
272
273  // Append the padding field
274  AppendField(getNextFieldOffsetInBytes(), NumBytes, Ty);
275}
276
277uint64_t CGRecordLayoutBuilder::getNextFieldOffsetInBytes() const {
278  if (FieldInfos.empty())
279    return 0;
280
281  const FieldInfo &LastInfo = FieldInfos.back();
282  return LastInfo.OffsetInBytes + LastInfo.SizeInBytes;
283}
284
285unsigned CGRecordLayoutBuilder::getTypeAlignment(const llvm::Type *Ty) const {
286  if (Packed)
287    return 1;
288
289  return Types.getTargetData().getABITypeAlignment(Ty);
290}
291
292uint64_t CGRecordLayoutBuilder::getTypeSizeInBytes(const llvm::Type *Ty) const {
293  return Types.getTargetData().getTypeAllocSize(Ty);
294}
295
296CGRecordLayout *
297CGRecordLayoutBuilder::ComputeLayout(CodeGenTypes &Types,
298                                     const RecordDecl *D) {
299  CGRecordLayoutBuilder Builder(Types);
300
301  Builder.Layout(D);
302
303  // FIXME: Once this works well enough, enable it.
304  return 0;
305
306  // FIXME: Use a VMContext.
307  const llvm::Type *Ty = llvm::StructType::get(Builder.FieldTypes,
308                                               Builder.Packed);
309
310  // Add all the field numbers.
311  for (unsigned i = 0, e = Builder.LLVMFields.size(); i != e; ++i) {
312    const FieldDecl *FD = Builder.LLVMFields[i].first;
313    unsigned FieldNo = Builder.LLVMFields[i].second;
314
315    Types.addFieldInfo(FD, FieldNo);
316  }
317
318  // Add bitfield info.
319  for (unsigned i = 0, e = Builder.LLVMBitFields.size(); i != e; ++i) {
320    const LLVMBitFieldInfo &Info = Builder.LLVMBitFields[i];
321
322    Types.addBitFieldInfo(Info.FD, Info.FieldNo, Info.Start, Info.Size);
323  }
324
325  return new CGRecordLayout(Ty, llvm::SmallSet<unsigned, 8>());
326}
327