CGExprConstant.cpp revision 7ead5c7b6fd48cf549e55b4db499c26ecf88ae75 
1//===--- CGExprConstant.cpp - Emit LLVM Code from Constant Expressions ----===//
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 contains code to emit Constant Expr nodes as LLVM code.
11//
12//===----------------------------------------------------------------------===//
13
14#include "CodeGenFunction.h"
15#include "CodeGenModule.h"
16#include "CGCXXABI.h"
17#include "CGObjCRuntime.h"
18#include "CGRecordLayout.h"
19#include "clang/AST/APValue.h"
20#include "clang/AST/ASTContext.h"
21#include "clang/AST/RecordLayout.h"
22#include "clang/AST/StmtVisitor.h"
23#include "clang/Basic/Builtins.h"
24#include "llvm/Constants.h"
25#include "llvm/Function.h"
26#include "llvm/GlobalVariable.h"
27#include "llvm/Target/TargetData.h"
28using namespace clang;
29using namespace CodeGen;
30
31//===----------------------------------------------------------------------===//
32//                            ConstStructBuilder
33//===----------------------------------------------------------------------===//
34
35namespace {
36class ConstStructBuilder {
37  CodeGenModule &CGM;
38  CodeGenFunction *CGF;
39
40  bool Packed;
41  CharUnits NextFieldOffsetInChars;
42  CharUnits LLVMStructAlignment;
43  std::vector<llvm::Constant *> Elements;
44public:
45  static llvm::Constant *BuildStruct(CodeGenModule &CGM, CodeGenFunction *CGF,
46                                     InitListExpr *ILE);
47
48private:
49  ConstStructBuilder(CodeGenModule &CGM, CodeGenFunction *CGF)
50    : CGM(CGM), CGF(CGF), Packed(false),
51    NextFieldOffsetInChars(CharUnits::Zero()),
52    LLVMStructAlignment(CharUnits::One()) { }
53
54  bool AppendField(const FieldDecl *Field, uint64_t FieldOffset,
55                   llvm::Constant *InitExpr);
56
57  void AppendBitField(const FieldDecl *Field, uint64_t FieldOffset,
58                      llvm::ConstantInt *InitExpr);
59
60  void AppendPadding(CharUnits PadSize);
61
62  void AppendTailPadding(CharUnits RecordSize);
63
64  void ConvertStructToPacked();
65
66  bool Build(InitListExpr *ILE);
67
68  CharUnits getAlignment(const llvm::Constant *C) const {
69    if (Packed)  return CharUnits::One();
70    return CharUnits::fromQuantity(
71        CGM.getTargetData().getABITypeAlignment(C->getType()));
72  }
73
74  CharUnits getSizeInChars(const llvm::Constant *C) const {
75    return CharUnits::fromQuantity(
76        CGM.getTargetData().getTypeAllocSize(C->getType()));
77  }
78};
79
80bool ConstStructBuilder::
81AppendField(const FieldDecl *Field, uint64_t FieldOffset,
82            llvm::Constant *InitCst) {
83
84  const ASTContext &Context = CGM.getContext();
85
86  CharUnits FieldOffsetInChars = Context.toCharUnitsFromBits(FieldOffset);
87
88  assert(NextFieldOffsetInChars <= FieldOffsetInChars
89         && "Field offset mismatch!");
90
91  CharUnits FieldAlignment = getAlignment(InitCst);
92
93  // Round up the field offset to the alignment of the field type.
94  CharUnits AlignedNextFieldOffsetInChars =
95    NextFieldOffsetInChars.RoundUpToAlignment(FieldAlignment);
96
97  if (AlignedNextFieldOffsetInChars > FieldOffsetInChars) {
98    assert(!Packed && "Alignment is wrong even with a packed struct!");
99
100    // Convert the struct to a packed struct.
101    ConvertStructToPacked();
102
103    AlignedNextFieldOffsetInChars = NextFieldOffsetInChars;
104  }
105
106  if (AlignedNextFieldOffsetInChars < FieldOffsetInChars) {
107    // We need to append padding.
108    AppendPadding(
109        FieldOffsetInChars - NextFieldOffsetInChars);
110
111    assert(NextFieldOffsetInChars == FieldOffsetInChars &&
112           "Did not add enough padding!");
113
114    AlignedNextFieldOffsetInChars = NextFieldOffsetInChars;
115  }
116
117  // Add the field.
118  Elements.push_back(InitCst);
119  NextFieldOffsetInChars = AlignedNextFieldOffsetInChars +
120                           getSizeInChars(InitCst);
121
122  if (Packed)
123    assert(LLVMStructAlignment == CharUnits::One() &&
124           "Packed struct not byte-aligned!");
125  else
126    LLVMStructAlignment = std::max(LLVMStructAlignment, FieldAlignment);
127
128  return true;
129}
130
131void ConstStructBuilder::AppendBitField(const FieldDecl *Field,
132                                        uint64_t FieldOffset,
133                                        llvm::ConstantInt *CI) {
134  const ASTContext &Context = CGM.getContext();
135  const uint64_t CharWidth = Context.getCharWidth();
136  uint64_t NextFieldOffsetInBits = Context.toBits(NextFieldOffsetInChars);
137  if (FieldOffset > NextFieldOffsetInBits) {
138    // We need to add padding.
139    CharUnits PadSize = Context.toCharUnitsFromBits(
140      llvm::RoundUpToAlignment(FieldOffset - NextFieldOffsetInBits,
141                               Context.getTargetInfo().getCharAlign()));
142
143    AppendPadding(PadSize);
144  }
145
146  uint64_t FieldSize = Field->getBitWidthValue(Context);
147
148  llvm::APInt FieldValue = CI->getValue();
149
150  // Promote the size of FieldValue if necessary
151  // FIXME: This should never occur, but currently it can because initializer
152  // constants are cast to bool, and because clang is not enforcing bitfield
153  // width limits.
154  if (FieldSize > FieldValue.getBitWidth())
155    FieldValue = FieldValue.zext(FieldSize);
156
157  // Truncate the size of FieldValue to the bit field size.
158  if (FieldSize < FieldValue.getBitWidth())
159    FieldValue = FieldValue.trunc(FieldSize);
160
161  NextFieldOffsetInBits = Context.toBits(NextFieldOffsetInChars);
162  if (FieldOffset < NextFieldOffsetInBits) {
163    // Either part of the field or the entire field can go into the previous
164    // byte.
165    assert(!Elements.empty() && "Elements can't be empty!");
166
167    unsigned BitsInPreviousByte = NextFieldOffsetInBits - FieldOffset;
168
169    bool FitsCompletelyInPreviousByte =
170      BitsInPreviousByte >= FieldValue.getBitWidth();
171
172    llvm::APInt Tmp = FieldValue;
173
174    if (!FitsCompletelyInPreviousByte) {
175      unsigned NewFieldWidth = FieldSize - BitsInPreviousByte;
176
177      if (CGM.getTargetData().isBigEndian()) {
178        Tmp = Tmp.lshr(NewFieldWidth);
179        Tmp = Tmp.trunc(BitsInPreviousByte);
180
181        // We want the remaining high bits.
182        FieldValue = FieldValue.trunc(NewFieldWidth);
183      } else {
184        Tmp = Tmp.trunc(BitsInPreviousByte);
185
186        // We want the remaining low bits.
187        FieldValue = FieldValue.lshr(BitsInPreviousByte);
188        FieldValue = FieldValue.trunc(NewFieldWidth);
189      }
190    }
191
192    Tmp = Tmp.zext(CharWidth);
193    if (CGM.getTargetData().isBigEndian()) {
194      if (FitsCompletelyInPreviousByte)
195        Tmp = Tmp.shl(BitsInPreviousByte - FieldValue.getBitWidth());
196    } else {
197      Tmp = Tmp.shl(CharWidth - BitsInPreviousByte);
198    }
199
200    // 'or' in the bits that go into the previous byte.
201    llvm::Value *LastElt = Elements.back();
202    if (llvm::ConstantInt *Val = dyn_cast<llvm::ConstantInt>(LastElt))
203      Tmp |= Val->getValue();
204    else {
205      assert(isa<llvm::UndefValue>(LastElt));
206      // If there is an undef field that we're adding to, it can either be a
207      // scalar undef (in which case, we just replace it with our field) or it
208      // is an array.  If it is an array, we have to pull one byte off the
209      // array so that the other undef bytes stay around.
210      if (!isa<llvm::IntegerType>(LastElt->getType())) {
211        // The undef padding will be a multibyte array, create a new smaller
212        // padding and then an hole for our i8 to get plopped into.
213        assert(isa<llvm::ArrayType>(LastElt->getType()) &&
214               "Expected array padding of undefs");
215        llvm::ArrayType *AT = cast<llvm::ArrayType>(LastElt->getType());
216        assert(AT->getElementType()->isIntegerTy(CharWidth) &&
217               AT->getNumElements() != 0 &&
218               "Expected non-empty array padding of undefs");
219
220        // Remove the padding array.
221        NextFieldOffsetInChars -= CharUnits::fromQuantity(AT->getNumElements());
222        Elements.pop_back();
223
224        // Add the padding back in two chunks.
225        AppendPadding(CharUnits::fromQuantity(AT->getNumElements()-1));
226        AppendPadding(CharUnits::One());
227        assert(isa<llvm::UndefValue>(Elements.back()) &&
228               Elements.back()->getType()->isIntegerTy(CharWidth) &&
229               "Padding addition didn't work right");
230      }
231    }
232
233    Elements.back() = llvm::ConstantInt::get(CGM.getLLVMContext(), Tmp);
234
235    if (FitsCompletelyInPreviousByte)
236      return;
237  }
238
239  while (FieldValue.getBitWidth() > CharWidth) {
240    llvm::APInt Tmp;
241
242    if (CGM.getTargetData().isBigEndian()) {
243      // We want the high bits.
244      Tmp =
245        FieldValue.lshr(FieldValue.getBitWidth() - CharWidth).trunc(CharWidth);
246    } else {
247      // We want the low bits.
248      Tmp = FieldValue.trunc(CharWidth);
249
250      FieldValue = FieldValue.lshr(CharWidth);
251    }
252
253    Elements.push_back(llvm::ConstantInt::get(CGM.getLLVMContext(), Tmp));
254    ++NextFieldOffsetInChars;
255
256    FieldValue = FieldValue.trunc(FieldValue.getBitWidth() - CharWidth);
257  }
258
259  assert(FieldValue.getBitWidth() > 0 &&
260         "Should have at least one bit left!");
261  assert(FieldValue.getBitWidth() <= CharWidth &&
262         "Should not have more than a byte left!");
263
264  if (FieldValue.getBitWidth() < CharWidth) {
265    if (CGM.getTargetData().isBigEndian()) {
266      unsigned BitWidth = FieldValue.getBitWidth();
267
268      FieldValue = FieldValue.zext(CharWidth) << (CharWidth - BitWidth);
269    } else
270      FieldValue = FieldValue.zext(CharWidth);
271  }
272
273  // Append the last element.
274  Elements.push_back(llvm::ConstantInt::get(CGM.getLLVMContext(),
275                                            FieldValue));
276  ++NextFieldOffsetInChars;
277}
278
279void ConstStructBuilder::AppendPadding(CharUnits PadSize) {
280  if (PadSize.isZero())
281    return;
282
283  llvm::Type *Ty = llvm::Type::getInt8Ty(CGM.getLLVMContext());
284  if (PadSize > CharUnits::One())
285    Ty = llvm::ArrayType::get(Ty, PadSize.getQuantity());
286
287  llvm::Constant *C = llvm::UndefValue::get(Ty);
288  Elements.push_back(C);
289  assert(getAlignment(C) == CharUnits::One() &&
290         "Padding must have 1 byte alignment!");
291
292  NextFieldOffsetInChars += getSizeInChars(C);
293}
294
295void ConstStructBuilder::AppendTailPadding(CharUnits RecordSize) {
296  assert(NextFieldOffsetInChars <= RecordSize &&
297         "Size mismatch!");
298
299  AppendPadding(RecordSize - NextFieldOffsetInChars);
300}
301
302void ConstStructBuilder::ConvertStructToPacked() {
303  std::vector<llvm::Constant *> PackedElements;
304  CharUnits ElementOffsetInChars = CharUnits::Zero();
305
306  for (unsigned i = 0, e = Elements.size(); i != e; ++i) {
307    llvm::Constant *C = Elements[i];
308
309    CharUnits ElementAlign = CharUnits::fromQuantity(
310      CGM.getTargetData().getABITypeAlignment(C->getType()));
311    CharUnits AlignedElementOffsetInChars =
312      ElementOffsetInChars.RoundUpToAlignment(ElementAlign);
313
314    if (AlignedElementOffsetInChars > ElementOffsetInChars) {
315      // We need some padding.
316      CharUnits NumChars =
317        AlignedElementOffsetInChars - ElementOffsetInChars;
318
319      llvm::Type *Ty = llvm::Type::getInt8Ty(CGM.getLLVMContext());
320      if (NumChars > CharUnits::One())
321        Ty = llvm::ArrayType::get(Ty, NumChars.getQuantity());
322
323      llvm::Constant *Padding = llvm::UndefValue::get(Ty);
324      PackedElements.push_back(Padding);
325      ElementOffsetInChars += getSizeInChars(Padding);
326    }
327
328    PackedElements.push_back(C);
329    ElementOffsetInChars += getSizeInChars(C);
330  }
331
332  assert(ElementOffsetInChars == NextFieldOffsetInChars &&
333         "Packing the struct changed its size!");
334
335  Elements = PackedElements;
336  LLVMStructAlignment = CharUnits::One();
337  Packed = true;
338}
339
340bool ConstStructBuilder::Build(InitListExpr *ILE) {
341  RecordDecl *RD = ILE->getType()->getAs<RecordType>()->getDecl();
342  const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
343
344  unsigned FieldNo = 0;
345  unsigned ElementNo = 0;
346  const FieldDecl *LastFD = 0;
347  bool IsMsStruct = RD->hasAttr<MsStructAttr>();
348
349  for (RecordDecl::field_iterator Field = RD->field_begin(),
350       FieldEnd = RD->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
351    if (IsMsStruct) {
352      // Zero-length bitfields following non-bitfield members are
353      // ignored:
354      if (CGM.getContext().ZeroBitfieldFollowsNonBitfield((*Field), LastFD)) {
355        --FieldNo;
356        continue;
357      }
358      LastFD = (*Field);
359    }
360
361    // If this is a union, skip all the fields that aren't being initialized.
362    if (RD->isUnion() && ILE->getInitializedFieldInUnion() != *Field)
363      continue;
364
365    // Don't emit anonymous bitfields, they just affect layout.
366    if (Field->isUnnamedBitfield()) {
367      LastFD = (*Field);
368      continue;
369    }
370
371    // Get the initializer.  A struct can include fields without initializers,
372    // we just use explicit null values for them.
373    llvm::Constant *EltInit;
374    if (ElementNo < ILE->getNumInits())
375      EltInit = CGM.EmitConstantExpr(ILE->getInit(ElementNo++),
376                                     Field->getType(), CGF);
377    else
378      EltInit = CGM.EmitNullConstant(Field->getType());
379
380    if (!EltInit)
381      return false;
382
383    if (!Field->isBitField()) {
384      // Handle non-bitfield members.
385      if (!AppendField(*Field, Layout.getFieldOffset(FieldNo), EltInit))
386        return false;
387    } else {
388      // Otherwise we have a bitfield.
389      AppendBitField(*Field, Layout.getFieldOffset(FieldNo),
390                     cast<llvm::ConstantInt>(EltInit));
391    }
392  }
393
394  CharUnits LayoutSizeInChars = Layout.getSize();
395
396  if (NextFieldOffsetInChars > LayoutSizeInChars) {
397    // If the struct is bigger than the size of the record type,
398    // we must have a flexible array member at the end.
399    assert(RD->hasFlexibleArrayMember() &&
400           "Must have flexible array member if struct is bigger than type!");
401
402    // No tail padding is necessary.
403    return true;
404  }
405
406  CharUnits LLVMSizeInChars =
407    NextFieldOffsetInChars.RoundUpToAlignment(LLVMStructAlignment);
408
409  // Check if we need to convert the struct to a packed struct.
410  if (NextFieldOffsetInChars <= LayoutSizeInChars &&
411      LLVMSizeInChars > LayoutSizeInChars) {
412    assert(!Packed && "Size mismatch!");
413
414    ConvertStructToPacked();
415    assert(NextFieldOffsetInChars <= LayoutSizeInChars &&
416           "Converting to packed did not help!");
417  }
418
419  // Append tail padding if necessary.
420  AppendTailPadding(LayoutSizeInChars);
421
422  assert(LayoutSizeInChars == NextFieldOffsetInChars &&
423         "Tail padding mismatch!");
424
425  return true;
426}
427
428llvm::Constant *ConstStructBuilder::
429  BuildStruct(CodeGenModule &CGM, CodeGenFunction *CGF, InitListExpr *ILE) {
430  ConstStructBuilder Builder(CGM, CGF);
431
432  if (!Builder.Build(ILE))
433    return 0;
434
435  // Pick the type to use.  If the type is layout identical to the ConvertType
436  // type then use it, otherwise use whatever the builder produced for us.
437  llvm::StructType *STy =
438      llvm::ConstantStruct::getTypeForElements(CGM.getLLVMContext(),
439                                               Builder.Elements,Builder.Packed);
440  llvm::Type *ILETy = CGM.getTypes().ConvertType(ILE->getType());
441  if (llvm::StructType *ILESTy = dyn_cast<llvm::StructType>(ILETy)) {
442    if (ILESTy->isLayoutIdentical(STy))
443      STy = ILESTy;
444  }
445
446  llvm::Constant *Result =
447    llvm::ConstantStruct::get(STy, Builder.Elements);
448
449  assert(Builder.NextFieldOffsetInChars.RoundUpToAlignment(
450           Builder.getAlignment(Result)) ==
451         Builder.getSizeInChars(Result) && "Size mismatch!");
452
453  return Result;
454}
455
456
457//===----------------------------------------------------------------------===//
458//                             ConstExprEmitter
459//===----------------------------------------------------------------------===//
460
461class ConstExprEmitter :
462  public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
463  CodeGenModule &CGM;
464  CodeGenFunction *CGF;
465  llvm::LLVMContext &VMContext;
466public:
467  ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
468    : CGM(cgm), CGF(cgf), VMContext(cgm.getLLVMContext()) {
469  }
470
471  //===--------------------------------------------------------------------===//
472  //                            Visitor Methods
473  //===--------------------------------------------------------------------===//
474
475  llvm::Constant *VisitStmt(Stmt *S) {
476    return 0;
477  }
478
479  llvm::Constant *VisitParenExpr(ParenExpr *PE) {
480    return Visit(PE->getSubExpr());
481  }
482
483  llvm::Constant *
484  VisitSubstNonTypeTemplateParmExpr(SubstNonTypeTemplateParmExpr *PE) {
485    return Visit(PE->getReplacement());
486  }
487
488  llvm::Constant *VisitGenericSelectionExpr(GenericSelectionExpr *GE) {
489    return Visit(GE->getResultExpr());
490  }
491
492  llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
493    return Visit(E->getInitializer());
494  }
495
496  llvm::Constant *VisitUnaryAddrOf(UnaryOperator *E) {
497    if (E->getType()->isMemberPointerType())
498      return CGM.getMemberPointerConstant(E);
499
500    return 0;
501  }
502
503  llvm::Constant *VisitCastExpr(CastExpr* E) {
504    Expr *subExpr = E->getSubExpr();
505    llvm::Constant *C = CGM.EmitConstantExpr(subExpr, subExpr->getType(), CGF);
506    if (!C) return 0;
507
508    llvm::Type *destType = ConvertType(E->getType());
509
510    switch (E->getCastKind()) {
511    case CK_ToUnion: {
512      // GCC cast to union extension
513      assert(E->getType()->isUnionType() &&
514             "Destination type is not union type!");
515
516      // Build a struct with the union sub-element as the first member,
517      // and padded to the appropriate size
518      std::vector<llvm::Constant*> Elts;
519      std::vector<llvm::Type*> Types;
520      Elts.push_back(C);
521      Types.push_back(C->getType());
522      unsigned CurSize = CGM.getTargetData().getTypeAllocSize(C->getType());
523      unsigned TotalSize = CGM.getTargetData().getTypeAllocSize(destType);
524
525      assert(CurSize <= TotalSize && "Union size mismatch!");
526      if (unsigned NumPadBytes = TotalSize - CurSize) {
527        llvm::Type *Ty = llvm::Type::getInt8Ty(VMContext);
528        if (NumPadBytes > 1)
529          Ty = llvm::ArrayType::get(Ty, NumPadBytes);
530
531        Elts.push_back(llvm::UndefValue::get(Ty));
532        Types.push_back(Ty);
533      }
534
535      llvm::StructType* STy =
536        llvm::StructType::get(C->getType()->getContext(), Types, false);
537      return llvm::ConstantStruct::get(STy, Elts);
538    }
539    case CK_NullToMemberPointer: {
540      const MemberPointerType *MPT = E->getType()->getAs<MemberPointerType>();
541      return CGM.getCXXABI().EmitNullMemberPointer(MPT);
542    }
543
544    case CK_DerivedToBaseMemberPointer:
545    case CK_BaseToDerivedMemberPointer:
546      return CGM.getCXXABI().EmitMemberPointerConversion(C, E);
547
548    case CK_LValueToRValue:
549    case CK_NoOp:
550      return C;
551
552    case CK_Dependent: llvm_unreachable("saw dependent cast!");
553
554    // These will never be supported.
555    case CK_ObjCObjectLValueCast:
556    case CK_ToVoid:
557    case CK_Dynamic:
558    case CK_ARCProduceObject:
559    case CK_ARCConsumeObject:
560    case CK_ARCReclaimReturnedObject:
561    case CK_ARCExtendBlockObject:
562    case CK_LValueBitCast:
563      return 0;
564
565    // These might need to be supported for constexpr.
566    case CK_UserDefinedConversion:
567    case CK_ConstructorConversion:
568      return 0;
569
570    // These don't need to be handled here because Evaluate knows how to
571    // evaluate all scalar expressions which can be constant-evaluated.
572    case CK_CPointerToObjCPointerCast:
573    case CK_BlockPointerToObjCPointerCast:
574    case CK_AnyPointerToBlockPointerCast:
575    case CK_BitCast:
576    case CK_ArrayToPointerDecay:
577    case CK_FunctionToPointerDecay:
578    case CK_BaseToDerived:
579    case CK_DerivedToBase:
580    case CK_UncheckedDerivedToBase:
581    case CK_MemberPointerToBoolean:
582    case CK_VectorSplat:
583    case CK_FloatingRealToComplex:
584    case CK_FloatingComplexToReal:
585    case CK_FloatingComplexToBoolean:
586    case CK_FloatingComplexCast:
587    case CK_FloatingComplexToIntegralComplex:
588    case CK_IntegralRealToComplex:
589    case CK_IntegralComplexToReal:
590    case CK_IntegralComplexToBoolean:
591    case CK_IntegralComplexCast:
592    case CK_IntegralComplexToFloatingComplex:
593    case CK_PointerToIntegral:
594    case CK_PointerToBoolean:
595    case CK_NullToPointer:
596    case CK_IntegralCast:
597    case CK_IntegralToPointer:
598    case CK_IntegralToBoolean:
599    case CK_IntegralToFloating:
600    case CK_FloatingToIntegral:
601    case CK_FloatingToBoolean:
602    case CK_FloatingCast:
603      return 0;
604    }
605    llvm_unreachable("Invalid CastKind");
606  }
607
608  llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
609    return Visit(DAE->getExpr());
610  }
611
612  llvm::Constant *VisitMaterializeTemporaryExpr(MaterializeTemporaryExpr *E) {
613    return Visit(E->GetTemporaryExpr());
614  }
615
616  llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
617    unsigned NumInitElements = ILE->getNumInits();
618    if (NumInitElements == 1 && ILE->getType() == ILE->getInit(0)->getType() &&
619        (isa<StringLiteral>(ILE->getInit(0)) ||
620         isa<ObjCEncodeExpr>(ILE->getInit(0))))
621      return Visit(ILE->getInit(0));
622
623    std::vector<llvm::Constant*> Elts;
624    llvm::ArrayType *AType =
625        cast<llvm::ArrayType>(ConvertType(ILE->getType()));
626    llvm::Type *ElemTy = AType->getElementType();
627    unsigned NumElements = AType->getNumElements();
628
629    // Initialising an array requires us to automatically
630    // initialise any elements that have not been initialised explicitly
631    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
632
633    // Copy initializer elements.
634    unsigned i = 0;
635    bool RewriteType = false;
636    for (; i < NumInitableElts; ++i) {
637      Expr *Init = ILE->getInit(i);
638      llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
639      if (!C)
640        return 0;
641      RewriteType |= (C->getType() != ElemTy);
642      Elts.push_back(C);
643    }
644
645    // Initialize remaining array elements.
646    // FIXME: This doesn't handle member pointers correctly!
647    llvm::Constant *fillC;
648    if (Expr *filler = ILE->getArrayFiller())
649      fillC = CGM.EmitConstantExpr(filler, filler->getType(), CGF);
650    else
651      fillC = llvm::Constant::getNullValue(ElemTy);
652    if (!fillC)
653      return 0;
654    RewriteType |= (fillC->getType() != ElemTy);
655    for (; i < NumElements; ++i)
656      Elts.push_back(fillC);
657
658    if (RewriteType) {
659      // FIXME: Try to avoid packing the array
660      std::vector<llvm::Type*> Types;
661      for (unsigned i = 0; i < Elts.size(); ++i)
662        Types.push_back(Elts[i]->getType());
663      llvm::StructType *SType = llvm::StructType::get(AType->getContext(),
664                                                            Types, true);
665      return llvm::ConstantStruct::get(SType, Elts);
666    }
667
668    return llvm::ConstantArray::get(AType, Elts);
669  }
670
671  llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
672    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
673  }
674
675  llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
676    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
677  }
678
679  llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
680    return CGM.EmitNullConstant(E->getType());
681  }
682
683  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
684    if (ILE->getType()->isArrayType())
685      return EmitArrayInitialization(ILE);
686
687    if (ILE->getType()->isRecordType())
688      return EmitStructInitialization(ILE);
689
690    if (ILE->getType()->isUnionType())
691      return EmitUnionInitialization(ILE);
692
693    return 0;
694  }
695
696  llvm::Constant *VisitCXXConstructExpr(CXXConstructExpr *E) {
697    if (!E->getConstructor()->isTrivial())
698      return 0;
699
700    QualType Ty = E->getType();
701
702    // FIXME: We should not have to call getBaseElementType here.
703    const RecordType *RT =
704      CGM.getContext().getBaseElementType(Ty)->getAs<RecordType>();
705    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
706
707    // If the class doesn't have a trivial destructor, we can't emit it as a
708    // constant expr.
709    if (!RD->hasTrivialDestructor())
710      return 0;
711
712    // Only copy and default constructors can be trivial.
713
714
715    if (E->getNumArgs()) {
716      assert(E->getNumArgs() == 1 && "trivial ctor with > 1 argument");
717      assert(E->getConstructor()->isCopyOrMoveConstructor() &&
718             "trivial ctor has argument but isn't a copy/move ctor");
719
720      Expr *Arg = E->getArg(0);
721      assert(CGM.getContext().hasSameUnqualifiedType(Ty, Arg->getType()) &&
722             "argument to copy ctor is of wrong type");
723
724      return Visit(Arg);
725    }
726
727    return CGM.EmitNullConstant(Ty);
728  }
729
730  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
731    return CGM.GetConstantArrayFromStringLiteral(E);
732  }
733
734  llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
735    // This must be an @encode initializing an array in a static initializer.
736    // Don't emit it as the address of the string, emit the string data itself
737    // as an inline array.
738    std::string Str;
739    CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
740    const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
741
742    // Resize the string to the right size, adding zeros at the end, or
743    // truncating as needed.
744    Str.resize(CAT->getSize().getZExtValue(), '\0');
745    return llvm::ConstantArray::get(VMContext, Str, false);
746  }
747
748  llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
749    return Visit(E->getSubExpr());
750  }
751
752  // Utility methods
753  llvm::Type *ConvertType(QualType T) {
754    return CGM.getTypes().ConvertType(T);
755  }
756
757public:
758  llvm::Constant *EmitLValue(APValue::LValueBase LVBase) {
759    if (const ValueDecl *Decl = LVBase.dyn_cast<const ValueDecl*>()) {
760      if (Decl->hasAttr<WeakRefAttr>())
761        return CGM.GetWeakRefReference(Decl);
762      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
763        return CGM.GetAddrOfFunction(FD);
764      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
765        // We can never refer to a variable with local storage.
766        if (!VD->hasLocalStorage()) {
767          if (VD->isFileVarDecl() || VD->hasExternalStorage())
768            return CGM.GetAddrOfGlobalVar(VD);
769          else if (VD->isLocalVarDecl()) {
770            assert(CGF && "Can't access static local vars without CGF");
771            return CGF->GetAddrOfStaticLocalVar(VD);
772          }
773        }
774      }
775      return 0;
776    }
777
778    Expr *E = const_cast<Expr*>(LVBase.get<const Expr*>());
779    switch (E->getStmtClass()) {
780    default: break;
781    case Expr::CompoundLiteralExprClass: {
782      // Note that due to the nature of compound literals, this is guaranteed
783      // to be the only use of the variable, so we just generate it here.
784      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
785      llvm::Constant* C = CGM.EmitConstantExpr(CLE->getInitializer(),
786                                               CLE->getType(), CGF);
787      // FIXME: "Leaked" on failure.
788      if (C)
789        C = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
790                                     E->getType().isConstant(CGM.getContext()),
791                                     llvm::GlobalValue::InternalLinkage,
792                                     C, ".compoundliteral", 0, false,
793                          CGM.getContext().getTargetAddressSpace(E->getType()));
794      return C;
795    }
796    case Expr::StringLiteralClass:
797      return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
798    case Expr::ObjCEncodeExprClass:
799      return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
800    case Expr::ObjCStringLiteralClass: {
801      ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
802      llvm::Constant *C =
803          CGM.getObjCRuntime().GenerateConstantString(SL->getString());
804      return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
805    }
806    case Expr::PredefinedExprClass: {
807      unsigned Type = cast<PredefinedExpr>(E)->getIdentType();
808      if (CGF) {
809        LValue Res = CGF->EmitPredefinedLValue(cast<PredefinedExpr>(E));
810        return cast<llvm::Constant>(Res.getAddress());
811      } else if (Type == PredefinedExpr::PrettyFunction) {
812        return CGM.GetAddrOfConstantCString("top level", ".tmp");
813      }
814
815      return CGM.GetAddrOfConstantCString("", ".tmp");
816    }
817    case Expr::AddrLabelExprClass: {
818      assert(CGF && "Invalid address of label expression outside function.");
819      llvm::Constant *Ptr =
820        CGF->GetAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
821      return llvm::ConstantExpr::getBitCast(Ptr, ConvertType(E->getType()));
822    }
823    case Expr::CallExprClass: {
824      CallExpr* CE = cast<CallExpr>(E);
825      unsigned builtin = CE->isBuiltinCall();
826      if (builtin !=
827            Builtin::BI__builtin___CFStringMakeConstantString &&
828          builtin !=
829            Builtin::BI__builtin___NSStringMakeConstantString)
830        break;
831      const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
832      const StringLiteral *Literal = cast<StringLiteral>(Arg);
833      if (builtin ==
834            Builtin::BI__builtin___NSStringMakeConstantString) {
835        return CGM.getObjCRuntime().GenerateConstantString(Literal);
836      }
837      // FIXME: need to deal with UCN conversion issues.
838      return CGM.GetAddrOfConstantCFString(Literal);
839    }
840    case Expr::BlockExprClass: {
841      std::string FunctionName;
842      if (CGF)
843        FunctionName = CGF->CurFn->getName();
844      else
845        FunctionName = "global";
846
847      return CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
848    }
849    case Expr::CXXTypeidExprClass: {
850      CXXTypeidExpr *Typeid = cast<CXXTypeidExpr>(E);
851      QualType T;
852      if (Typeid->isTypeOperand())
853        T = Typeid->getTypeOperand();
854      else
855        T = Typeid->getExprOperand()->getType();
856      return CGM.GetAddrOfRTTIDescriptor(T);
857    }
858    }
859
860    return 0;
861  }
862};
863
864}  // end anonymous namespace.
865
866llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
867                                                QualType DestType,
868                                                CodeGenFunction *CGF) {
869  Expr::EvalResult Result;
870
871  bool Success = false;
872
873  if (DestType->isReferenceType())
874    Success = E->EvaluateAsLValue(Result, Context);
875  else
876    Success = E->EvaluateAsRValue(Result, Context);
877
878  if (Success && !Result.HasSideEffects) {
879    switch (Result.Val.getKind()) {
880    case APValue::Uninitialized:
881      llvm_unreachable("Constant expressions should be initialized.");
882    case APValue::LValue: {
883      llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
884      llvm::Constant *Offset =
885        llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext),
886                               Result.Val.getLValueOffset().getQuantity());
887
888      llvm::Constant *C;
889      if (APValue::LValueBase LVBase = Result.Val.getLValueBase()) {
890        C = ConstExprEmitter(*this, CGF).EmitLValue(LVBase);
891
892        // Apply offset if necessary.
893        if (!Offset->isNullValue()) {
894          llvm::Type *Type = llvm::Type::getInt8PtrTy(VMContext);
895          llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
896          Casted = llvm::ConstantExpr::getGetElementPtr(Casted, Offset);
897          C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
898        }
899
900        // Convert to the appropriate type; this could be an lvalue for
901        // an integer.
902        if (isa<llvm::PointerType>(DestTy))
903          return llvm::ConstantExpr::getBitCast(C, DestTy);
904
905        return llvm::ConstantExpr::getPtrToInt(C, DestTy);
906      } else {
907        C = Offset;
908
909        // Convert to the appropriate type; this could be an lvalue for
910        // an integer.
911        if (isa<llvm::PointerType>(DestTy))
912          return llvm::ConstantExpr::getIntToPtr(C, DestTy);
913
914        // If the types don't match this should only be a truncate.
915        if (C->getType() != DestTy)
916          return llvm::ConstantExpr::getTrunc(C, DestTy);
917
918        return C;
919      }
920    }
921    case APValue::Int: {
922      llvm::Constant *C = llvm::ConstantInt::get(VMContext,
923                                                 Result.Val.getInt());
924
925      if (C->getType()->isIntegerTy(1)) {
926        llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
927        C = llvm::ConstantExpr::getZExt(C, BoolTy);
928      }
929      return C;
930    }
931    case APValue::ComplexInt: {
932      llvm::Constant *Complex[2];
933
934      Complex[0] = llvm::ConstantInt::get(VMContext,
935                                          Result.Val.getComplexIntReal());
936      Complex[1] = llvm::ConstantInt::get(VMContext,
937                                          Result.Val.getComplexIntImag());
938
939      // FIXME: the target may want to specify that this is packed.
940      llvm::StructType *STy = llvm::StructType::get(Complex[0]->getType(),
941                                                    Complex[1]->getType(),
942                                                    NULL);
943      return llvm::ConstantStruct::get(STy, Complex);
944    }
945    case APValue::Float: {
946      const llvm::APFloat &Init = Result.Val.getFloat();
947      if (&Init.getSemantics() == &llvm::APFloat::IEEEhalf)
948        return llvm::ConstantInt::get(VMContext, Init.bitcastToAPInt());
949      else
950        return llvm::ConstantFP::get(VMContext, Init);
951    }
952    case APValue::ComplexFloat: {
953      llvm::Constant *Complex[2];
954
955      Complex[0] = llvm::ConstantFP::get(VMContext,
956                                         Result.Val.getComplexFloatReal());
957      Complex[1] = llvm::ConstantFP::get(VMContext,
958                                         Result.Val.getComplexFloatImag());
959
960      // FIXME: the target may want to specify that this is packed.
961      llvm::StructType *STy = llvm::StructType::get(Complex[0]->getType(),
962                                                    Complex[1]->getType(),
963                                                    NULL);
964      return llvm::ConstantStruct::get(STy, Complex);
965    }
966    case APValue::Vector: {
967      SmallVector<llvm::Constant *, 4> Inits;
968      unsigned NumElts = Result.Val.getVectorLength();
969
970      if (Context.getLangOptions().AltiVec &&
971          isa<CastExpr>(E) &&
972          cast<CastExpr>(E)->getCastKind() == CK_VectorSplat) {
973        // AltiVec vector initialization with a single literal
974        APValue &Elt = Result.Val.getVectorElt(0);
975
976        llvm::Constant* InitValue = Elt.isInt()
977          ? cast<llvm::Constant>
978              (llvm::ConstantInt::get(VMContext, Elt.getInt()))
979          : cast<llvm::Constant>
980              (llvm::ConstantFP::get(VMContext, Elt.getFloat()));
981
982        for (unsigned i = 0; i != NumElts; ++i)
983          Inits.push_back(InitValue);
984
985      } else {
986        for (unsigned i = 0; i != NumElts; ++i) {
987          APValue &Elt = Result.Val.getVectorElt(i);
988          if (Elt.isInt())
989            Inits.push_back(llvm::ConstantInt::get(VMContext, Elt.getInt()));
990          else
991            Inits.push_back(llvm::ConstantFP::get(VMContext, Elt.getFloat()));
992        }
993      }
994      return llvm::ConstantVector::get(Inits);
995    }
996    case APValue::AddrLabelDiff: {
997      const AddrLabelExpr *LHSExpr = Result.Val.getAddrLabelDiffLHS();
998      const AddrLabelExpr *RHSExpr = Result.Val.getAddrLabelDiffRHS();
999      llvm::Constant *LHS = EmitConstantExpr(LHSExpr, LHSExpr->getType(), CGF);
1000      llvm::Constant *RHS = EmitConstantExpr(RHSExpr, RHSExpr->getType(), CGF);
1001
1002      // Compute difference
1003      llvm::Type *ResultType = getTypes().ConvertType(E->getType());
1004      LHS = llvm::ConstantExpr::getPtrToInt(LHS, IntPtrTy);
1005      RHS = llvm::ConstantExpr::getPtrToInt(RHS, IntPtrTy);
1006      llvm::Constant *AddrLabelDiff = llvm::ConstantExpr::getSub(LHS, RHS);
1007
1008      // LLVM is a bit sensitive about the exact format of the
1009      // address-of-label difference; make sure to truncate after
1010      // the subtraction.
1011      return llvm::ConstantExpr::getTruncOrBitCast(AddrLabelDiff, ResultType);
1012    }
1013    case APValue::Array:
1014    case APValue::Struct:
1015    case APValue::Union:
1016    case APValue::MemberPointer:
1017      break;
1018    }
1019  }
1020
1021  llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
1022  if (C && C->getType()->isIntegerTy(1)) {
1023    llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
1024    C = llvm::ConstantExpr::getZExt(C, BoolTy);
1025  }
1026  return C;
1027}
1028
1029llvm::Constant *
1030CodeGenModule::GetAddrOfConstantCompoundLiteral(const CompoundLiteralExpr *E) {
1031  assert(E->isFileScope() && "not a file-scope compound literal expr");
1032  return ConstExprEmitter(*this, 0).EmitLValue(E);
1033}
1034
1035static uint64_t getFieldOffset(ASTContext &C, const FieldDecl *field) {
1036  const ASTRecordLayout &layout = C.getASTRecordLayout(field->getParent());
1037  return layout.getFieldOffset(field->getFieldIndex());
1038}
1039
1040llvm::Constant *
1041CodeGenModule::getMemberPointerConstant(const UnaryOperator *uo) {
1042  // Member pointer constants always have a very particular form.
1043  const MemberPointerType *type = cast<MemberPointerType>(uo->getType());
1044  const ValueDecl *decl = cast<DeclRefExpr>(uo->getSubExpr())->getDecl();
1045
1046  // A member function pointer.
1047  if (const CXXMethodDecl *method = dyn_cast<CXXMethodDecl>(decl))
1048    return getCXXABI().EmitMemberPointer(method);
1049
1050  // Otherwise, a member data pointer.
1051  uint64_t fieldOffset;
1052  if (const FieldDecl *field = dyn_cast<FieldDecl>(decl))
1053    fieldOffset = getFieldOffset(getContext(), field);
1054  else {
1055    const IndirectFieldDecl *ifield = cast<IndirectFieldDecl>(decl);
1056
1057    fieldOffset = 0;
1058    for (IndirectFieldDecl::chain_iterator ci = ifield->chain_begin(),
1059           ce = ifield->chain_end(); ci != ce; ++ci)
1060      fieldOffset += getFieldOffset(getContext(), cast<FieldDecl>(*ci));
1061  }
1062
1063  CharUnits chars = getContext().toCharUnitsFromBits((int64_t) fieldOffset);
1064  return getCXXABI().EmitMemberDataPointer(type, chars);
1065}
1066
1067static void
1068FillInNullDataMemberPointers(CodeGenModule &CGM, QualType T,
1069                             std::vector<llvm::Constant *> &Elements,
1070                             uint64_t StartOffset) {
1071  assert(StartOffset % CGM.getContext().getCharWidth() == 0 &&
1072         "StartOffset not byte aligned!");
1073
1074  if (CGM.getTypes().isZeroInitializable(T))
1075    return;
1076
1077  if (const ConstantArrayType *CAT =
1078        CGM.getContext().getAsConstantArrayType(T)) {
1079    QualType ElementTy = CAT->getElementType();
1080    uint64_t ElementSize = CGM.getContext().getTypeSize(ElementTy);
1081
1082    for (uint64_t I = 0, E = CAT->getSize().getZExtValue(); I != E; ++I) {
1083      FillInNullDataMemberPointers(CGM, ElementTy, Elements,
1084                                   StartOffset + I * ElementSize);
1085    }
1086  } else if (const RecordType *RT = T->getAs<RecordType>()) {
1087    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
1088    const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
1089
1090    // Go through all bases and fill in any null pointer to data members.
1091    for (CXXRecordDecl::base_class_const_iterator I = RD->bases_begin(),
1092         E = RD->bases_end(); I != E; ++I) {
1093      if (I->isVirtual()) {
1094        // Ignore virtual bases.
1095        continue;
1096      }
1097
1098      const CXXRecordDecl *BaseDecl =
1099      cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());
1100
1101      // Ignore empty bases.
1102      if (BaseDecl->isEmpty())
1103        continue;
1104
1105      // Ignore bases that don't have any pointer to data members.
1106      if (CGM.getTypes().isZeroInitializable(BaseDecl))
1107        continue;
1108
1109      uint64_t BaseOffset = Layout.getBaseClassOffsetInBits(BaseDecl);
1110      FillInNullDataMemberPointers(CGM, I->getType(),
1111                                   Elements, StartOffset + BaseOffset);
1112    }
1113
1114    // Visit all fields.
1115    unsigned FieldNo = 0;
1116    for (RecordDecl::field_iterator I = RD->field_begin(),
1117         E = RD->field_end(); I != E; ++I, ++FieldNo) {
1118      QualType FieldType = I->getType();
1119
1120      if (CGM.getTypes().isZeroInitializable(FieldType))
1121        continue;
1122
1123      uint64_t FieldOffset = StartOffset + Layout.getFieldOffset(FieldNo);
1124      FillInNullDataMemberPointers(CGM, FieldType, Elements, FieldOffset);
1125    }
1126  } else {
1127    assert(T->isMemberPointerType() && "Should only see member pointers here!");
1128    assert(!T->getAs<MemberPointerType>()->getPointeeType()->isFunctionType() &&
1129           "Should only see pointers to data members here!");
1130
1131    CharUnits StartIndex = CGM.getContext().toCharUnitsFromBits(StartOffset);
1132    CharUnits EndIndex = StartIndex + CGM.getContext().getTypeSizeInChars(T);
1133
1134    // FIXME: hardcodes Itanium member pointer representation!
1135    llvm::Constant *NegativeOne =
1136      llvm::ConstantInt::get(llvm::Type::getInt8Ty(CGM.getLLVMContext()),
1137                             -1ULL, /*isSigned*/true);
1138
1139    // Fill in the null data member pointer.
1140    for (CharUnits I = StartIndex; I != EndIndex; ++I)
1141      Elements[I.getQuantity()] = NegativeOne;
1142  }
1143}
1144
1145static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
1146                                               llvm::Type *baseType,
1147                                               const CXXRecordDecl *base);
1148
1149static llvm::Constant *EmitNullConstant(CodeGenModule &CGM,
1150                                        const CXXRecordDecl *record,
1151                                        bool asCompleteObject) {
1152  const CGRecordLayout &layout = CGM.getTypes().getCGRecordLayout(record);
1153  llvm::StructType *structure =
1154    (asCompleteObject ? layout.getLLVMType()
1155                      : layout.getBaseSubobjectLLVMType());
1156
1157  unsigned numElements = structure->getNumElements();
1158  std::vector<llvm::Constant *> elements(numElements);
1159
1160  // Fill in all the bases.
1161  for (CXXRecordDecl::base_class_const_iterator
1162         I = record->bases_begin(), E = record->bases_end(); I != E; ++I) {
1163    if (I->isVirtual()) {
1164      // Ignore virtual bases; if we're laying out for a complete
1165      // object, we'll lay these out later.
1166      continue;
1167    }
1168
1169    const CXXRecordDecl *base =
1170      cast<CXXRecordDecl>(I->getType()->castAs<RecordType>()->getDecl());
1171
1172    // Ignore empty bases.
1173    if (base->isEmpty())
1174      continue;
1175
1176    unsigned fieldIndex = layout.getNonVirtualBaseLLVMFieldNo(base);
1177    llvm::Type *baseType = structure->getElementType(fieldIndex);
1178    elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
1179  }
1180
1181  // Fill in all the fields.
1182  for (RecordDecl::field_iterator I = record->field_begin(),
1183         E = record->field_end(); I != E; ++I) {
1184    const FieldDecl *field = *I;
1185
1186    // Fill in non-bitfields. (Bitfields always use a zero pattern, which we
1187    // will fill in later.)
1188    if (!field->isBitField()) {
1189      unsigned fieldIndex = layout.getLLVMFieldNo(field);
1190      elements[fieldIndex] = CGM.EmitNullConstant(field->getType());
1191    }
1192
1193    // For unions, stop after the first named field.
1194    if (record->isUnion() && field->getDeclName())
1195      break;
1196  }
1197
1198  // Fill in the virtual bases, if we're working with the complete object.
1199  if (asCompleteObject) {
1200    for (CXXRecordDecl::base_class_const_iterator
1201           I = record->vbases_begin(), E = record->vbases_end(); I != E; ++I) {
1202      const CXXRecordDecl *base =
1203        cast<CXXRecordDecl>(I->getType()->castAs<RecordType>()->getDecl());
1204
1205      // Ignore empty bases.
1206      if (base->isEmpty())
1207        continue;
1208
1209      unsigned fieldIndex = layout.getVirtualBaseIndex(base);
1210
1211      // We might have already laid this field out.
1212      if (elements[fieldIndex]) continue;
1213
1214      llvm::Type *baseType = structure->getElementType(fieldIndex);
1215      elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
1216    }
1217  }
1218
1219  // Now go through all other fields and zero them out.
1220  for (unsigned i = 0; i != numElements; ++i) {
1221    if (!elements[i])
1222      elements[i] = llvm::Constant::getNullValue(structure->getElementType(i));
1223  }
1224
1225  return llvm::ConstantStruct::get(structure, elements);
1226}
1227
1228/// Emit the null constant for a base subobject.
1229static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
1230                                               llvm::Type *baseType,
1231                                               const CXXRecordDecl *base) {
1232  const CGRecordLayout &baseLayout = CGM.getTypes().getCGRecordLayout(base);
1233
1234  // Just zero out bases that don't have any pointer to data members.
1235  if (baseLayout.isZeroInitializableAsBase())
1236    return llvm::Constant::getNullValue(baseType);
1237
1238  // If the base type is a struct, we can just use its null constant.
1239  if (isa<llvm::StructType>(baseType)) {
1240    return EmitNullConstant(CGM, base, /*complete*/ false);
1241  }
1242
1243  // Otherwise, some bases are represented as arrays of i8 if the size
1244  // of the base is smaller than its corresponding LLVM type.  Figure
1245  // out how many elements this base array has.
1246  llvm::ArrayType *baseArrayType = cast<llvm::ArrayType>(baseType);
1247  unsigned numBaseElements = baseArrayType->getNumElements();
1248
1249  // Fill in null data member pointers.
1250  std::vector<llvm::Constant *> baseElements(numBaseElements);
1251  FillInNullDataMemberPointers(CGM, CGM.getContext().getTypeDeclType(base),
1252                               baseElements, 0);
1253
1254  // Now go through all other elements and zero them out.
1255  if (numBaseElements) {
1256    llvm::Type *i8 = llvm::Type::getInt8Ty(CGM.getLLVMContext());
1257    llvm::Constant *i8_zero = llvm::Constant::getNullValue(i8);
1258    for (unsigned i = 0; i != numBaseElements; ++i) {
1259      if (!baseElements[i])
1260        baseElements[i] = i8_zero;
1261    }
1262  }
1263
1264  return llvm::ConstantArray::get(baseArrayType, baseElements);
1265}
1266
1267llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
1268  if (getTypes().isZeroInitializable(T))
1269    return llvm::Constant::getNullValue(getTypes().ConvertTypeForMem(T));
1270
1271  if (const ConstantArrayType *CAT = Context.getAsConstantArrayType(T)) {
1272
1273    QualType ElementTy = CAT->getElementType();
1274
1275    llvm::Constant *Element = EmitNullConstant(ElementTy);
1276    unsigned NumElements = CAT->getSize().getZExtValue();
1277    std::vector<llvm::Constant *> Array(NumElements);
1278    for (unsigned i = 0; i != NumElements; ++i)
1279      Array[i] = Element;
1280
1281    llvm::ArrayType *ATy =
1282      cast<llvm::ArrayType>(getTypes().ConvertTypeForMem(T));
1283    return llvm::ConstantArray::get(ATy, Array);
1284  }
1285
1286  if (const RecordType *RT = T->getAs<RecordType>()) {
1287    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
1288    return ::EmitNullConstant(*this, RD, /*complete object*/ true);
1289  }
1290
1291  assert(T->isMemberPointerType() && "Should only see member pointers here!");
1292  assert(!T->getAs<MemberPointerType>()->getPointeeType()->isFunctionType() &&
1293         "Should only see pointers to data members here!");
1294
1295  // Itanium C++ ABI 2.3:
1296  //   A NULL pointer is represented as -1.
1297  return getCXXABI().EmitNullMemberPointer(T->castAs<MemberPointerType>());
1298}
1299
1300llvm::Constant *
1301CodeGenModule::EmitNullConstantForBase(const CXXRecordDecl *Record) {
1302  return ::EmitNullConstant(*this, Record, false);
1303}
1304