CGRecordLayoutBuilder.cpp revision 21fd7d7347358994ee6d944c22a51e82d22409d9 
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  Alignment = Types.getContext().getASTRecordLayout(D).getAlignment() / 8;
31  Packed = D->hasAttr<PackedAttr>();
32
33  if (D->isUnion()) {
34    LayoutUnion(D);
35    return;
36  }
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  NextFieldOffsetInBytes = 0;
45  FieldTypes.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 = NextFieldOffsetInBytes * 8;
61  unsigned NumBytesToAppend;
62
63  if (FieldOffset < NextFieldOffset) {
64    assert(BitsAvailableInLastField && "Bitfield size mismatch!");
65    assert(NextFieldOffsetInBytes && "Must have laid out at least one byte!");
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  BitsAvailableInLastField =
92    NextFieldOffsetInBytes * 8 - (FieldOffset + FieldSize);
93}
94
95bool CGRecordLayoutBuilder::LayoutField(const FieldDecl *D,
96                                        uint64_t FieldOffset) {
97  // If the field is packed, then we need a packed struct.
98  if (!Packed && D->hasAttr<PackedAttr>())
99    return false;
100
101  if (D->isBitField()) {
102    // We must use packed structs for unnamed bit fields since they
103    // don't affect the struct alignment.
104    if (!Packed && !D->getDeclName())
105      return false;
106
107    LayoutBitField(D, FieldOffset);
108    return true;
109  }
110
111  assert(FieldOffset % 8 == 0 && "FieldOffset is not on a byte boundary!");
112  uint64_t FieldOffsetInBytes = FieldOffset / 8;
113
114  const llvm::Type *Ty = Types.ConvertTypeForMemRecursive(D->getType());
115  unsigned TypeAlignment = getTypeAlignment(Ty);
116
117  // If the type alignment is larger then the struct alignment, we must use
118  // a packed struct.
119  if (TypeAlignment > Alignment) {
120    assert(!Packed && "Alignment is wrong even with packed struct!");
121    return false;
122  }
123
124  if (const RecordType *RT = D->getType()->getAs<RecordType>()) {
125    const RecordDecl *RD = cast<RecordDecl>(RT->getDecl());
126    if (const PragmaPackAttr *PPA = RD->getAttr<PragmaPackAttr>()) {
127      if (PPA->getAlignment() != TypeAlignment * 8 && !Packed)
128        return false;
129    }
130  }
131
132  // Round up the field offset to the alignment of the field type.
133  uint64_t AlignedNextFieldOffsetInBytes =
134    llvm::RoundUpToAlignment(NextFieldOffsetInBytes, TypeAlignment);
135
136  if (FieldOffsetInBytes < AlignedNextFieldOffsetInBytes) {
137    assert(!Packed && "Could not place field even with packed struct!");
138    return false;
139  }
140
141  if (AlignedNextFieldOffsetInBytes < FieldOffsetInBytes) {
142    // Even with alignment, the field offset is not at the right place,
143    // insert padding.
144    uint64_t PaddingInBytes = FieldOffsetInBytes - NextFieldOffsetInBytes;
145
146    AppendBytes(PaddingInBytes);
147  }
148
149  // Now append the field.
150  LLVMFields.push_back(LLVMFieldInfo(D, FieldTypes.size()));
151  AppendField(FieldOffsetInBytes, Ty);
152
153  return true;
154}
155
156void CGRecordLayoutBuilder::LayoutUnion(const RecordDecl *D) {
157  assert(D->isUnion() && "Can't call LayoutUnion on a non-union record!");
158
159  const ASTRecordLayout &Layout = Types.getContext().getASTRecordLayout(D);
160
161  const llvm::Type *Ty = 0;
162  uint64_t Size = 0;
163  unsigned Align = 0;
164
165  bool HasOnlyZeroSizedBitFields = true;
166
167  unsigned FieldNo = 0;
168  for (RecordDecl::field_iterator Field = D->field_begin(),
169       FieldEnd = D->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
170    assert(Layout.getFieldOffset(FieldNo) == 0 &&
171          "Union field offset did not start at the beginning of record!");
172
173    if (Field->isBitField()) {
174      uint64_t FieldSize =
175        Field->getBitWidth()->EvaluateAsInt(Types.getContext()).getZExtValue();
176
177      // Ignore zero sized bit fields.
178      if (FieldSize == 0)
179        continue;
180
181      // Add the bit field info.
182      Types.addBitFieldInfo(*Field, 0, 0, FieldSize);
183    } else
184      Types.addFieldInfo(*Field, 0);
185
186    HasOnlyZeroSizedBitFields = false;
187
188    const llvm::Type *FieldTy =
189      Types.ConvertTypeForMemRecursive(Field->getType());
190    unsigned FieldAlign = Types.getTargetData().getABITypeAlignment(FieldTy);
191    uint64_t FieldSize = Types.getTargetData().getTypeAllocSize(FieldTy);
192
193    if (FieldAlign < Align)
194      continue;
195
196    if (FieldAlign > Align || FieldSize > Size) {
197      Ty = FieldTy;
198      Align = FieldAlign;
199      Size = FieldSize;
200    }
201  }
202
203  // Now add our field.
204  if (Ty) {
205    AppendField(0, Ty);
206
207    if (getTypeAlignment(Ty) > Layout.getAlignment() / 8) {
208      // We need a packed struct.
209      Packed = true;
210      Align = 1;
211    }
212  }
213  if (!Align) {
214    assert(HasOnlyZeroSizedBitFields &&
215           "0-align record did not have all zero-sized bit-fields!");
216    Align = 1;
217  }
218
219  // Append tail padding.
220  if (Layout.getSize() / 8 > Size)
221    AppendPadding(Layout.getSize() / 8, Align);
222}
223
224void CGRecordLayoutBuilder::LayoutBases(const CXXRecordDecl *RD,
225                                        const ASTRecordLayout &Layout) {
226  // Check if we need to add a vtable pointer.
227  if (RD->isDynamicClass() && !Layout.getPrimaryBase()) {
228    const llvm::Type *Int8PtrTy =
229      llvm::Type::getInt8PtrTy(Types.getLLVMContext());
230
231    assert(NextFieldOffsetInBytes == 0 &&
232           "Vtable pointer must come first!");
233    AppendField(NextFieldOffsetInBytes, Int8PtrTy->getPointerTo());
234  }
235}
236
237bool CGRecordLayoutBuilder::LayoutFields(const RecordDecl *D) {
238  assert(!D->isUnion() && "Can't call LayoutFields on a union!");
239  assert(Alignment && "Did not set alignment!");
240
241  const ASTRecordLayout &Layout = Types.getContext().getASTRecordLayout(D);
242
243  if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D))
244    LayoutBases(RD, Layout);
245
246  unsigned FieldNo = 0;
247
248  for (RecordDecl::field_iterator Field = D->field_begin(),
249       FieldEnd = D->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
250    if (!LayoutField(*Field, Layout.getFieldOffset(FieldNo))) {
251      assert(!Packed &&
252             "Could not layout fields even with a packed LLVM struct!");
253      return false;
254    }
255  }
256
257  // Append tail padding if necessary.
258  AppendTailPadding(Layout.getSize());
259
260  return true;
261}
262
263void CGRecordLayoutBuilder::AppendTailPadding(uint64_t RecordSize) {
264  assert(RecordSize % 8 == 0 && "Invalid record size!");
265
266  uint64_t RecordSizeInBytes = RecordSize / 8;
267  assert(NextFieldOffsetInBytes <= RecordSizeInBytes && "Size mismatch!");
268
269  uint64_t AlignedNextFieldOffset =
270    llvm::RoundUpToAlignment(NextFieldOffsetInBytes, AlignmentAsLLVMStruct);
271
272  if (AlignedNextFieldOffset == RecordSizeInBytes) {
273    // We don't need any padding.
274    return;
275  }
276
277  unsigned NumPadBytes = RecordSizeInBytes - NextFieldOffsetInBytes;
278  AppendBytes(NumPadBytes);
279}
280
281void CGRecordLayoutBuilder::AppendField(uint64_t FieldOffsetInBytes,
282                                        const llvm::Type *FieldTy) {
283  AlignmentAsLLVMStruct = std::max(AlignmentAsLLVMStruct,
284                                   getTypeAlignment(FieldTy));
285
286  uint64_t FieldSizeInBytes = getTypeSizeInBytes(FieldTy);
287
288  FieldTypes.push_back(FieldTy);
289
290  NextFieldOffsetInBytes = FieldOffsetInBytes + FieldSizeInBytes;
291  BitsAvailableInLastField = 0;
292}
293
294void
295CGRecordLayoutBuilder::AppendPadding(uint64_t FieldOffsetInBytes,
296                                     const llvm::Type *FieldTy) {
297  AppendPadding(FieldOffsetInBytes, getTypeAlignment(FieldTy));
298}
299
300void CGRecordLayoutBuilder::AppendPadding(uint64_t FieldOffsetInBytes,
301                                          unsigned FieldAlignment) {
302  assert(NextFieldOffsetInBytes <= FieldOffsetInBytes &&
303         "Incorrect field layout!");
304
305  // Round up the field offset to the alignment of the field type.
306  uint64_t AlignedNextFieldOffsetInBytes =
307    llvm::RoundUpToAlignment(NextFieldOffsetInBytes, FieldAlignment);
308
309  if (AlignedNextFieldOffsetInBytes < FieldOffsetInBytes) {
310    // Even with alignment, the field offset is not at the right place,
311    // insert padding.
312    uint64_t PaddingInBytes = FieldOffsetInBytes - NextFieldOffsetInBytes;
313
314    AppendBytes(PaddingInBytes);
315  }
316}
317
318void CGRecordLayoutBuilder::AppendBytes(uint64_t NumBytes) {
319  if (NumBytes == 0)
320    return;
321
322  const llvm::Type *Ty = llvm::Type::getInt8Ty(Types.getLLVMContext());
323  if (NumBytes > 1)
324    Ty = llvm::ArrayType::get(Ty, NumBytes);
325
326  // Append the padding field
327  AppendField(NextFieldOffsetInBytes, Ty);
328}
329
330unsigned CGRecordLayoutBuilder::getTypeAlignment(const llvm::Type *Ty) const {
331  if (Packed)
332    return 1;
333
334  return Types.getTargetData().getABITypeAlignment(Ty);
335}
336
337uint64_t CGRecordLayoutBuilder::getTypeSizeInBytes(const llvm::Type *Ty) const {
338  return Types.getTargetData().getTypeAllocSize(Ty);
339}
340
341void CGRecordLayoutBuilder::CheckForMemberPointer(const FieldDecl *FD) {
342  // This record already contains a member pointer.
343  if (ContainsMemberPointer)
344    return;
345
346  // Can only have member pointers if we're compiling C++.
347  if (!Types.getContext().getLangOptions().CPlusPlus)
348    return;
349
350  QualType Ty = FD->getType();
351
352  if (Ty->isMemberPointerType()) {
353    // We have a member pointer!
354    ContainsMemberPointer = true;
355    return;
356  }
357
358}
359
360CGRecordLayout *
361CGRecordLayoutBuilder::ComputeLayout(CodeGenTypes &Types,
362                                     const RecordDecl *D) {
363  CGRecordLayoutBuilder Builder(Types);
364
365  Builder.Layout(D);
366
367  const llvm::Type *Ty = llvm::StructType::get(Types.getLLVMContext(),
368                                               Builder.FieldTypes,
369                                               Builder.Packed);
370  assert(Types.getContext().getASTRecordLayout(D).getSize() / 8 ==
371         Types.getTargetData().getTypeAllocSize(Ty) &&
372         "Type size mismatch!");
373
374  // Add all the field numbers.
375  for (unsigned i = 0, e = Builder.LLVMFields.size(); i != e; ++i) {
376    const FieldDecl *FD = Builder.LLVMFields[i].first;
377    unsigned FieldNo = Builder.LLVMFields[i].second;
378
379    Types.addFieldInfo(FD, FieldNo);
380  }
381
382  // Add bitfield info.
383  for (unsigned i = 0, e = Builder.LLVMBitFields.size(); i != e; ++i) {
384    const LLVMBitFieldInfo &Info = Builder.LLVMBitFields[i];
385
386    Types.addBitFieldInfo(Info.FD, Info.FieldNo, Info.Start, Info.Size);
387  }
388
389  return new CGRecordLayout(Ty, Builder.ContainsMemberPointer);
390}
391