CGExprConstant.cpp revision 1bf9a9e6a5bdc0de7939908855dcddf46b661800 
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 *VisitBinSub(BinaryOperator *E) {
504    // This must be a pointer/pointer subtraction.  This only happens for
505    // address of label.
506    if (!isa<AddrLabelExpr>(E->getLHS()->IgnoreParenNoopCasts(CGM.getContext())) ||
507       !isa<AddrLabelExpr>(E->getRHS()->IgnoreParenNoopCasts(CGM.getContext())))
508      return 0;
509
510    llvm::Constant *LHS = CGM.EmitConstantExpr(E->getLHS(),
511                                               E->getLHS()->getType(), CGF);
512    llvm::Constant *RHS = CGM.EmitConstantExpr(E->getRHS(),
513                                               E->getRHS()->getType(), CGF);
514
515    llvm::Type *ResultType = ConvertType(E->getType());
516    LHS = llvm::ConstantExpr::getPtrToInt(LHS, ResultType);
517    RHS = llvm::ConstantExpr::getPtrToInt(RHS, ResultType);
518
519    // No need to divide by element size, since addr of label is always void*,
520    // which has size 1 in GNUish.
521    return llvm::ConstantExpr::getSub(LHS, RHS);
522  }
523
524  llvm::Constant *VisitCastExpr(CastExpr* E) {
525    Expr *subExpr = E->getSubExpr();
526    llvm::Constant *C = CGM.EmitConstantExpr(subExpr, subExpr->getType(), CGF);
527    if (!C) return 0;
528
529    llvm::Type *destType = ConvertType(E->getType());
530
531    switch (E->getCastKind()) {
532    case CK_ToUnion: {
533      // GCC cast to union extension
534      assert(E->getType()->isUnionType() &&
535             "Destination type is not union type!");
536
537      // Build a struct with the union sub-element as the first member,
538      // and padded to the appropriate size
539      std::vector<llvm::Constant*> Elts;
540      std::vector<llvm::Type*> Types;
541      Elts.push_back(C);
542      Types.push_back(C->getType());
543      unsigned CurSize = CGM.getTargetData().getTypeAllocSize(C->getType());
544      unsigned TotalSize = CGM.getTargetData().getTypeAllocSize(destType);
545
546      assert(CurSize <= TotalSize && "Union size mismatch!");
547      if (unsigned NumPadBytes = TotalSize - CurSize) {
548        llvm::Type *Ty = llvm::Type::getInt8Ty(VMContext);
549        if (NumPadBytes > 1)
550          Ty = llvm::ArrayType::get(Ty, NumPadBytes);
551
552        Elts.push_back(llvm::UndefValue::get(Ty));
553        Types.push_back(Ty);
554      }
555
556      llvm::StructType* STy =
557        llvm::StructType::get(C->getType()->getContext(), Types, false);
558      return llvm::ConstantStruct::get(STy, Elts);
559    }
560    case CK_NullToMemberPointer: {
561      const MemberPointerType *MPT = E->getType()->getAs<MemberPointerType>();
562      return CGM.getCXXABI().EmitNullMemberPointer(MPT);
563    }
564
565    case CK_DerivedToBaseMemberPointer:
566    case CK_BaseToDerivedMemberPointer:
567      return CGM.getCXXABI().EmitMemberPointerConversion(C, E);
568
569    case CK_LValueToRValue:
570    case CK_NoOp:
571      return C;
572
573    case CK_CPointerToObjCPointerCast:
574    case CK_BlockPointerToObjCPointerCast:
575    case CK_AnyPointerToBlockPointerCast:
576    case CK_BitCast:
577      if (C->getType() == destType) return C;
578      return llvm::ConstantExpr::getBitCast(C, destType);
579
580    case CK_Dependent: llvm_unreachable("saw dependent cast!");
581
582    // These will never be supported.
583    case CK_ObjCObjectLValueCast:
584    case CK_ToVoid:
585    case CK_Dynamic:
586    case CK_ARCProduceObject:
587    case CK_ARCConsumeObject:
588    case CK_ARCReclaimReturnedObject:
589    case CK_ARCExtendBlockObject:
590    case CK_LValueBitCast:
591      return 0;
592
593    // These might need to be supported for constexpr.
594    case CK_UserDefinedConversion:
595    case CK_ConstructorConversion:
596      return 0;
597
598    // These should eventually be supported.
599    case CK_ArrayToPointerDecay:
600    case CK_FunctionToPointerDecay:
601    case CK_BaseToDerived:
602    case CK_DerivedToBase:
603    case CK_UncheckedDerivedToBase:
604    case CK_MemberPointerToBoolean:
605    case CK_VectorSplat:
606    case CK_FloatingRealToComplex:
607    case CK_FloatingComplexToReal:
608    case CK_FloatingComplexToBoolean:
609    case CK_FloatingComplexCast:
610    case CK_FloatingComplexToIntegralComplex:
611    case CK_IntegralRealToComplex:
612    case CK_IntegralComplexToReal:
613    case CK_IntegralComplexToBoolean:
614    case CK_IntegralComplexCast:
615    case CK_IntegralComplexToFloatingComplex:
616      return 0;
617
618    case CK_PointerToIntegral:
619      if (!E->getType()->isBooleanType())
620        return llvm::ConstantExpr::getPtrToInt(C, destType);
621      // fallthrough
622
623    case CK_PointerToBoolean:
624      return llvm::ConstantExpr::getICmp(llvm::CmpInst::ICMP_EQ, C,
625        llvm::ConstantPointerNull::get(cast<llvm::PointerType>(C->getType())));
626
627    case CK_NullToPointer:
628      return llvm::ConstantPointerNull::get(cast<llvm::PointerType>(destType));
629
630    case CK_IntegralCast: {
631      bool isSigned = subExpr->getType()->isSignedIntegerOrEnumerationType();
632      return llvm::ConstantExpr::getIntegerCast(C, destType, isSigned);
633    }
634
635    case CK_IntegralToPointer: {
636      bool isSigned = subExpr->getType()->isSignedIntegerOrEnumerationType();
637      C = llvm::ConstantExpr::getIntegerCast(C, CGM.IntPtrTy, isSigned);
638      return llvm::ConstantExpr::getIntToPtr(C, destType);
639    }
640
641    case CK_IntegralToBoolean:
642      return llvm::ConstantExpr::getICmp(llvm::CmpInst::ICMP_EQ, C,
643                             llvm::Constant::getNullValue(C->getType()));
644
645    case CK_IntegralToFloating:
646      if (subExpr->getType()->isSignedIntegerOrEnumerationType())
647        return llvm::ConstantExpr::getSIToFP(C, destType);
648      else
649        return llvm::ConstantExpr::getUIToFP(C, destType);
650
651    case CK_FloatingToIntegral:
652      if (E->getType()->isSignedIntegerOrEnumerationType())
653        return llvm::ConstantExpr::getFPToSI(C, destType);
654      else
655        return llvm::ConstantExpr::getFPToUI(C, destType);
656
657    case CK_FloatingToBoolean:
658      return llvm::ConstantExpr::getFCmp(llvm::CmpInst::FCMP_UNE, C,
659                             llvm::Constant::getNullValue(C->getType()));
660
661    case CK_FloatingCast:
662      return llvm::ConstantExpr::getFPCast(C, destType);
663    }
664    llvm_unreachable("Invalid CastKind");
665  }
666
667  llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
668    return Visit(DAE->getExpr());
669  }
670
671  llvm::Constant *VisitMaterializeTemporaryExpr(MaterializeTemporaryExpr *E) {
672    return Visit(E->GetTemporaryExpr());
673  }
674
675  llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
676    unsigned NumInitElements = ILE->getNumInits();
677    if (NumInitElements == 1 && ILE->getType() == ILE->getInit(0)->getType() &&
678        (isa<StringLiteral>(ILE->getInit(0)) ||
679         isa<ObjCEncodeExpr>(ILE->getInit(0))))
680      return Visit(ILE->getInit(0));
681
682    std::vector<llvm::Constant*> Elts;
683    llvm::ArrayType *AType =
684        cast<llvm::ArrayType>(ConvertType(ILE->getType()));
685    llvm::Type *ElemTy = AType->getElementType();
686    unsigned NumElements = AType->getNumElements();
687
688    // Initialising an array requires us to automatically
689    // initialise any elements that have not been initialised explicitly
690    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
691
692    // Copy initializer elements.
693    unsigned i = 0;
694    bool RewriteType = false;
695    for (; i < NumInitableElts; ++i) {
696      Expr *Init = ILE->getInit(i);
697      llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
698      if (!C)
699        return 0;
700      RewriteType |= (C->getType() != ElemTy);
701      Elts.push_back(C);
702    }
703
704    // Initialize remaining array elements.
705    // FIXME: This doesn't handle member pointers correctly!
706    llvm::Constant *fillC;
707    if (Expr *filler = ILE->getArrayFiller())
708      fillC = CGM.EmitConstantExpr(filler, filler->getType(), CGF);
709    else
710      fillC = llvm::Constant::getNullValue(ElemTy);
711    if (!fillC)
712      return 0;
713    RewriteType |= (fillC->getType() != ElemTy);
714    for (; i < NumElements; ++i)
715      Elts.push_back(fillC);
716
717    if (RewriteType) {
718      // FIXME: Try to avoid packing the array
719      std::vector<llvm::Type*> Types;
720      for (unsigned i = 0; i < Elts.size(); ++i)
721        Types.push_back(Elts[i]->getType());
722      llvm::StructType *SType = llvm::StructType::get(AType->getContext(),
723                                                            Types, true);
724      return llvm::ConstantStruct::get(SType, Elts);
725    }
726
727    return llvm::ConstantArray::get(AType, Elts);
728  }
729
730  llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
731    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
732  }
733
734  llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
735    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
736  }
737
738  llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
739    return CGM.EmitNullConstant(E->getType());
740  }
741
742  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
743    if (ILE->getType()->isAnyComplexType() && ILE->getNumInits() == 2) {
744      // Complex type with element initializers
745      Expr *Real = ILE->getInit(0);
746      Expr *Imag = ILE->getInit(1);
747      llvm::Constant *Complex[2];
748      Complex[0] = CGM.EmitConstantExpr(Real, Real->getType(), CGF);
749      if (!Complex[0])
750        return 0;
751      Complex[1] = CGM.EmitConstantExpr(Imag, Imag->getType(), CGF);
752      if (!Complex[1])
753        return 0;
754      llvm::StructType *STy =
755          cast<llvm::StructType>(ConvertType(ILE->getType()));
756      return llvm::ConstantStruct::get(STy, Complex);
757    }
758
759    if (ILE->getType()->isScalarType()) {
760      // We have a scalar in braces. Just use the first element.
761      if (ILE->getNumInits() > 0) {
762        Expr *Init = ILE->getInit(0);
763        return CGM.EmitConstantExpr(Init, Init->getType(), CGF);
764      }
765      return CGM.EmitNullConstant(ILE->getType());
766    }
767
768    if (ILE->getType()->isArrayType())
769      return EmitArrayInitialization(ILE);
770
771    if (ILE->getType()->isRecordType())
772      return EmitStructInitialization(ILE);
773
774    if (ILE->getType()->isUnionType())
775      return EmitUnionInitialization(ILE);
776
777    // If ILE was a constant vector, we would have handled it already.
778    if (ILE->getType()->isVectorType())
779      return 0;
780
781    llvm_unreachable("Unable to handle InitListExpr");
782  }
783
784  llvm::Constant *VisitCXXConstructExpr(CXXConstructExpr *E) {
785    if (!E->getConstructor()->isTrivial())
786      return 0;
787
788    QualType Ty = E->getType();
789
790    // FIXME: We should not have to call getBaseElementType here.
791    const RecordType *RT =
792      CGM.getContext().getBaseElementType(Ty)->getAs<RecordType>();
793    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
794
795    // If the class doesn't have a trivial destructor, we can't emit it as a
796    // constant expr.
797    if (!RD->hasTrivialDestructor())
798      return 0;
799
800    // Only copy and default constructors can be trivial.
801
802
803    if (E->getNumArgs()) {
804      assert(E->getNumArgs() == 1 && "trivial ctor with > 1 argument");
805      assert(E->getConstructor()->isCopyOrMoveConstructor() &&
806             "trivial ctor has argument but isn't a copy/move ctor");
807
808      Expr *Arg = E->getArg(0);
809      assert(CGM.getContext().hasSameUnqualifiedType(Ty, Arg->getType()) &&
810             "argument to copy ctor is of wrong type");
811
812      return Visit(Arg);
813    }
814
815    return CGM.EmitNullConstant(Ty);
816  }
817
818  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
819    return CGM.GetConstantArrayFromStringLiteral(E);
820  }
821
822  llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
823    // This must be an @encode initializing an array in a static initializer.
824    // Don't emit it as the address of the string, emit the string data itself
825    // as an inline array.
826    std::string Str;
827    CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
828    const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
829
830    // Resize the string to the right size, adding zeros at the end, or
831    // truncating as needed.
832    Str.resize(CAT->getSize().getZExtValue(), '\0');
833    return llvm::ConstantArray::get(VMContext, Str, false);
834  }
835
836  llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
837    return Visit(E->getSubExpr());
838  }
839
840  // Utility methods
841  llvm::Type *ConvertType(QualType T) {
842    return CGM.getTypes().ConvertType(T);
843  }
844
845public:
846  llvm::Constant *EmitLValue(APValue::LValueBase LVBase) {
847    if (const ValueDecl *Decl = LVBase.dyn_cast<const ValueDecl*>()) {
848      if (Decl->hasAttr<WeakRefAttr>())
849        return CGM.GetWeakRefReference(Decl);
850      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
851        return CGM.GetAddrOfFunction(FD);
852      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
853        // We can never refer to a variable with local storage.
854        if (!VD->hasLocalStorage()) {
855          if (VD->isFileVarDecl() || VD->hasExternalStorage())
856            return CGM.GetAddrOfGlobalVar(VD);
857          else if (VD->isLocalVarDecl()) {
858            assert(CGF && "Can't access static local vars without CGF");
859            return CGF->GetAddrOfStaticLocalVar(VD);
860          }
861        }
862      }
863      return 0;
864    }
865
866    Expr *E = const_cast<Expr*>(LVBase.get<const Expr*>());
867    switch (E->getStmtClass()) {
868    default: break;
869    case Expr::CompoundLiteralExprClass: {
870      // Note that due to the nature of compound literals, this is guaranteed
871      // to be the only use of the variable, so we just generate it here.
872      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
873      llvm::Constant* C = Visit(CLE->getInitializer());
874      // FIXME: "Leaked" on failure.
875      if (C)
876        C = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
877                                     E->getType().isConstant(CGM.getContext()),
878                                     llvm::GlobalValue::InternalLinkage,
879                                     C, ".compoundliteral", 0, false,
880                          CGM.getContext().getTargetAddressSpace(E->getType()));
881      return C;
882    }
883    case Expr::StringLiteralClass:
884      return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
885    case Expr::ObjCEncodeExprClass:
886      return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
887    case Expr::ObjCStringLiteralClass: {
888      ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
889      llvm::Constant *C =
890          CGM.getObjCRuntime().GenerateConstantString(SL->getString());
891      return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
892    }
893    case Expr::PredefinedExprClass: {
894      unsigned Type = cast<PredefinedExpr>(E)->getIdentType();
895      if (CGF) {
896        LValue Res = CGF->EmitPredefinedLValue(cast<PredefinedExpr>(E));
897        return cast<llvm::Constant>(Res.getAddress());
898      } else if (Type == PredefinedExpr::PrettyFunction) {
899        return CGM.GetAddrOfConstantCString("top level", ".tmp");
900      }
901
902      return CGM.GetAddrOfConstantCString("", ".tmp");
903    }
904    case Expr::AddrLabelExprClass: {
905      assert(CGF && "Invalid address of label expression outside function.");
906      llvm::Constant *Ptr =
907        CGF->GetAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
908      return llvm::ConstantExpr::getBitCast(Ptr, ConvertType(E->getType()));
909    }
910    case Expr::CallExprClass: {
911      CallExpr* CE = cast<CallExpr>(E);
912      unsigned builtin = CE->isBuiltinCall();
913      if (builtin !=
914            Builtin::BI__builtin___CFStringMakeConstantString &&
915          builtin !=
916            Builtin::BI__builtin___NSStringMakeConstantString)
917        break;
918      const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
919      const StringLiteral *Literal = cast<StringLiteral>(Arg);
920      if (builtin ==
921            Builtin::BI__builtin___NSStringMakeConstantString) {
922        return CGM.getObjCRuntime().GenerateConstantString(Literal);
923      }
924      // FIXME: need to deal with UCN conversion issues.
925      return CGM.GetAddrOfConstantCFString(Literal);
926    }
927    case Expr::BlockExprClass: {
928      std::string FunctionName;
929      if (CGF)
930        FunctionName = CGF->CurFn->getName();
931      else
932        FunctionName = "global";
933
934      return CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
935    }
936    }
937
938    return 0;
939  }
940};
941
942}  // end anonymous namespace.
943
944llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
945                                                QualType DestType,
946                                                CodeGenFunction *CGF) {
947  Expr::EvalResult Result;
948
949  bool Success = false;
950
951  if (DestType->isReferenceType())
952    Success = E->EvaluateAsLValue(Result, Context);
953  else
954    Success = E->EvaluateAsRValue(Result, Context);
955
956  if (Success && !Result.HasSideEffects) {
957    switch (Result.Val.getKind()) {
958    case APValue::Uninitialized:
959      llvm_unreachable("Constant expressions should be initialized.");
960    case APValue::LValue: {
961      llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
962      llvm::Constant *Offset =
963        llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext),
964                               Result.Val.getLValueOffset().getQuantity());
965
966      llvm::Constant *C;
967      if (APValue::LValueBase LVBase = Result.Val.getLValueBase()) {
968        C = ConstExprEmitter(*this, CGF).EmitLValue(LVBase);
969
970        // Apply offset if necessary.
971        if (!Offset->isNullValue()) {
972          llvm::Type *Type = llvm::Type::getInt8PtrTy(VMContext);
973          llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
974          Casted = llvm::ConstantExpr::getGetElementPtr(Casted, Offset);
975          C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
976        }
977
978        // Convert to the appropriate type; this could be an lvalue for
979        // an integer.
980        if (isa<llvm::PointerType>(DestTy))
981          return llvm::ConstantExpr::getBitCast(C, DestTy);
982
983        return llvm::ConstantExpr::getPtrToInt(C, DestTy);
984      } else {
985        C = Offset;
986
987        // Convert to the appropriate type; this could be an lvalue for
988        // an integer.
989        if (isa<llvm::PointerType>(DestTy))
990          return llvm::ConstantExpr::getIntToPtr(C, DestTy);
991
992        // If the types don't match this should only be a truncate.
993        if (C->getType() != DestTy)
994          return llvm::ConstantExpr::getTrunc(C, DestTy);
995
996        return C;
997      }
998    }
999    case APValue::Int: {
1000      llvm::Constant *C = llvm::ConstantInt::get(VMContext,
1001                                                 Result.Val.getInt());
1002
1003      if (C->getType()->isIntegerTy(1)) {
1004        llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
1005        C = llvm::ConstantExpr::getZExt(C, BoolTy);
1006      }
1007      return C;
1008    }
1009    case APValue::ComplexInt: {
1010      llvm::Constant *Complex[2];
1011
1012      Complex[0] = llvm::ConstantInt::get(VMContext,
1013                                          Result.Val.getComplexIntReal());
1014      Complex[1] = llvm::ConstantInt::get(VMContext,
1015                                          Result.Val.getComplexIntImag());
1016
1017      // FIXME: the target may want to specify that this is packed.
1018      llvm::StructType *STy = llvm::StructType::get(Complex[0]->getType(),
1019                                                    Complex[1]->getType(),
1020                                                    NULL);
1021      return llvm::ConstantStruct::get(STy, Complex);
1022    }
1023    case APValue::Float: {
1024      const llvm::APFloat &Init = Result.Val.getFloat();
1025      if (&Init.getSemantics() == &llvm::APFloat::IEEEhalf)
1026        return llvm::ConstantInt::get(VMContext, Init.bitcastToAPInt());
1027      else
1028        return llvm::ConstantFP::get(VMContext, Init);
1029    }
1030    case APValue::ComplexFloat: {
1031      llvm::Constant *Complex[2];
1032
1033      Complex[0] = llvm::ConstantFP::get(VMContext,
1034                                         Result.Val.getComplexFloatReal());
1035      Complex[1] = llvm::ConstantFP::get(VMContext,
1036                                         Result.Val.getComplexFloatImag());
1037
1038      // FIXME: the target may want to specify that this is packed.
1039      llvm::StructType *STy = llvm::StructType::get(Complex[0]->getType(),
1040                                                    Complex[1]->getType(),
1041                                                    NULL);
1042      return llvm::ConstantStruct::get(STy, Complex);
1043    }
1044    case APValue::Vector: {
1045      SmallVector<llvm::Constant *, 4> Inits;
1046      unsigned NumElts = Result.Val.getVectorLength();
1047
1048      if (Context.getLangOptions().AltiVec &&
1049          isa<CastExpr>(E) &&
1050          cast<CastExpr>(E)->getCastKind() == CK_VectorSplat) {
1051        // AltiVec vector initialization with a single literal
1052        APValue &Elt = Result.Val.getVectorElt(0);
1053
1054        llvm::Constant* InitValue = Elt.isInt()
1055          ? cast<llvm::Constant>
1056              (llvm::ConstantInt::get(VMContext, Elt.getInt()))
1057          : cast<llvm::Constant>
1058              (llvm::ConstantFP::get(VMContext, Elt.getFloat()));
1059
1060        for (unsigned i = 0; i != NumElts; ++i)
1061          Inits.push_back(InitValue);
1062
1063      } else {
1064        for (unsigned i = 0; i != NumElts; ++i) {
1065          APValue &Elt = Result.Val.getVectorElt(i);
1066          if (Elt.isInt())
1067            Inits.push_back(llvm::ConstantInt::get(VMContext, Elt.getInt()));
1068          else
1069            Inits.push_back(llvm::ConstantFP::get(VMContext, Elt.getFloat()));
1070        }
1071      }
1072      return llvm::ConstantVector::get(Inits);
1073    }
1074    case APValue::Array:
1075    case APValue::Struct:
1076    case APValue::Union:
1077      break;
1078    }
1079  }
1080
1081  llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
1082  if (C && C->getType()->isIntegerTy(1)) {
1083    llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
1084    C = llvm::ConstantExpr::getZExt(C, BoolTy);
1085  }
1086  return C;
1087}
1088
1089static uint64_t getFieldOffset(ASTContext &C, const FieldDecl *field) {
1090  const ASTRecordLayout &layout = C.getASTRecordLayout(field->getParent());
1091  return layout.getFieldOffset(field->getFieldIndex());
1092}
1093
1094llvm::Constant *
1095CodeGenModule::getMemberPointerConstant(const UnaryOperator *uo) {
1096  // Member pointer constants always have a very particular form.
1097  const MemberPointerType *type = cast<MemberPointerType>(uo->getType());
1098  const ValueDecl *decl = cast<DeclRefExpr>(uo->getSubExpr())->getDecl();
1099
1100  // A member function pointer.
1101  if (const CXXMethodDecl *method = dyn_cast<CXXMethodDecl>(decl))
1102    return getCXXABI().EmitMemberPointer(method);
1103
1104  // Otherwise, a member data pointer.
1105  uint64_t fieldOffset;
1106  if (const FieldDecl *field = dyn_cast<FieldDecl>(decl))
1107    fieldOffset = getFieldOffset(getContext(), field);
1108  else {
1109    const IndirectFieldDecl *ifield = cast<IndirectFieldDecl>(decl);
1110
1111    fieldOffset = 0;
1112    for (IndirectFieldDecl::chain_iterator ci = ifield->chain_begin(),
1113           ce = ifield->chain_end(); ci != ce; ++ci)
1114      fieldOffset += getFieldOffset(getContext(), cast<FieldDecl>(*ci));
1115  }
1116
1117  CharUnits chars = getContext().toCharUnitsFromBits((int64_t) fieldOffset);
1118  return getCXXABI().EmitMemberDataPointer(type, chars);
1119}
1120
1121static void
1122FillInNullDataMemberPointers(CodeGenModule &CGM, QualType T,
1123                             std::vector<llvm::Constant *> &Elements,
1124                             uint64_t StartOffset) {
1125  assert(StartOffset % CGM.getContext().getCharWidth() == 0 &&
1126         "StartOffset not byte aligned!");
1127
1128  if (CGM.getTypes().isZeroInitializable(T))
1129    return;
1130
1131  if (const ConstantArrayType *CAT =
1132        CGM.getContext().getAsConstantArrayType(T)) {
1133    QualType ElementTy = CAT->getElementType();
1134    uint64_t ElementSize = CGM.getContext().getTypeSize(ElementTy);
1135
1136    for (uint64_t I = 0, E = CAT->getSize().getZExtValue(); I != E; ++I) {
1137      FillInNullDataMemberPointers(CGM, ElementTy, Elements,
1138                                   StartOffset + I * ElementSize);
1139    }
1140  } else if (const RecordType *RT = T->getAs<RecordType>()) {
1141    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
1142    const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
1143
1144    // Go through all bases and fill in any null pointer to data members.
1145    for (CXXRecordDecl::base_class_const_iterator I = RD->bases_begin(),
1146         E = RD->bases_end(); I != E; ++I) {
1147      if (I->isVirtual()) {
1148        // Ignore virtual bases.
1149        continue;
1150      }
1151
1152      const CXXRecordDecl *BaseDecl =
1153      cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());
1154
1155      // Ignore empty bases.
1156      if (BaseDecl->isEmpty())
1157        continue;
1158
1159      // Ignore bases that don't have any pointer to data members.
1160      if (CGM.getTypes().isZeroInitializable(BaseDecl))
1161        continue;
1162
1163      uint64_t BaseOffset = Layout.getBaseClassOffsetInBits(BaseDecl);
1164      FillInNullDataMemberPointers(CGM, I->getType(),
1165                                   Elements, StartOffset + BaseOffset);
1166    }
1167
1168    // Visit all fields.
1169    unsigned FieldNo = 0;
1170    for (RecordDecl::field_iterator I = RD->field_begin(),
1171         E = RD->field_end(); I != E; ++I, ++FieldNo) {
1172      QualType FieldType = I->getType();
1173
1174      if (CGM.getTypes().isZeroInitializable(FieldType))
1175        continue;
1176
1177      uint64_t FieldOffset = StartOffset + Layout.getFieldOffset(FieldNo);
1178      FillInNullDataMemberPointers(CGM, FieldType, Elements, FieldOffset);
1179    }
1180  } else {
1181    assert(T->isMemberPointerType() && "Should only see member pointers here!");
1182    assert(!T->getAs<MemberPointerType>()->getPointeeType()->isFunctionType() &&
1183           "Should only see pointers to data members here!");
1184
1185    CharUnits StartIndex = CGM.getContext().toCharUnitsFromBits(StartOffset);
1186    CharUnits EndIndex = StartIndex + CGM.getContext().getTypeSizeInChars(T);
1187
1188    // FIXME: hardcodes Itanium member pointer representation!
1189    llvm::Constant *NegativeOne =
1190      llvm::ConstantInt::get(llvm::Type::getInt8Ty(CGM.getLLVMContext()),
1191                             -1ULL, /*isSigned*/true);
1192
1193    // Fill in the null data member pointer.
1194    for (CharUnits I = StartIndex; I != EndIndex; ++I)
1195      Elements[I.getQuantity()] = NegativeOne;
1196  }
1197}
1198
1199static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
1200                                               llvm::Type *baseType,
1201                                               const CXXRecordDecl *base);
1202
1203static llvm::Constant *EmitNullConstant(CodeGenModule &CGM,
1204                                        const CXXRecordDecl *record,
1205                                        bool asCompleteObject) {
1206  const CGRecordLayout &layout = CGM.getTypes().getCGRecordLayout(record);
1207  llvm::StructType *structure =
1208    (asCompleteObject ? layout.getLLVMType()
1209                      : layout.getBaseSubobjectLLVMType());
1210
1211  unsigned numElements = structure->getNumElements();
1212  std::vector<llvm::Constant *> elements(numElements);
1213
1214  // Fill in all the bases.
1215  for (CXXRecordDecl::base_class_const_iterator
1216         I = record->bases_begin(), E = record->bases_end(); I != E; ++I) {
1217    if (I->isVirtual()) {
1218      // Ignore virtual bases; if we're laying out for a complete
1219      // object, we'll lay these out later.
1220      continue;
1221    }
1222
1223    const CXXRecordDecl *base =
1224      cast<CXXRecordDecl>(I->getType()->castAs<RecordType>()->getDecl());
1225
1226    // Ignore empty bases.
1227    if (base->isEmpty())
1228      continue;
1229
1230    unsigned fieldIndex = layout.getNonVirtualBaseLLVMFieldNo(base);
1231    llvm::Type *baseType = structure->getElementType(fieldIndex);
1232    elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
1233  }
1234
1235  // Fill in all the fields.
1236  for (RecordDecl::field_iterator I = record->field_begin(),
1237         E = record->field_end(); I != E; ++I) {
1238    const FieldDecl *field = *I;
1239
1240    // Ignore bit fields.
1241    if (field->isBitField())
1242      continue;
1243
1244    unsigned fieldIndex = layout.getLLVMFieldNo(field);
1245    elements[fieldIndex] = CGM.EmitNullConstant(field->getType());
1246  }
1247
1248  // Fill in the virtual bases, if we're working with the complete object.
1249  if (asCompleteObject) {
1250    for (CXXRecordDecl::base_class_const_iterator
1251           I = record->vbases_begin(), E = record->vbases_end(); I != E; ++I) {
1252      const CXXRecordDecl *base =
1253        cast<CXXRecordDecl>(I->getType()->castAs<RecordType>()->getDecl());
1254
1255      // Ignore empty bases.
1256      if (base->isEmpty())
1257        continue;
1258
1259      unsigned fieldIndex = layout.getVirtualBaseIndex(base);
1260
1261      // We might have already laid this field out.
1262      if (elements[fieldIndex]) continue;
1263
1264      llvm::Type *baseType = structure->getElementType(fieldIndex);
1265      elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
1266    }
1267  }
1268
1269  // Now go through all other fields and zero them out.
1270  for (unsigned i = 0; i != numElements; ++i) {
1271    if (!elements[i])
1272      elements[i] = llvm::Constant::getNullValue(structure->getElementType(i));
1273  }
1274
1275  return llvm::ConstantStruct::get(structure, elements);
1276}
1277
1278/// Emit the null constant for a base subobject.
1279static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
1280                                               llvm::Type *baseType,
1281                                               const CXXRecordDecl *base) {
1282  const CGRecordLayout &baseLayout = CGM.getTypes().getCGRecordLayout(base);
1283
1284  // Just zero out bases that don't have any pointer to data members.
1285  if (baseLayout.isZeroInitializableAsBase())
1286    return llvm::Constant::getNullValue(baseType);
1287
1288  // If the base type is a struct, we can just use its null constant.
1289  if (isa<llvm::StructType>(baseType)) {
1290    return EmitNullConstant(CGM, base, /*complete*/ false);
1291  }
1292
1293  // Otherwise, some bases are represented as arrays of i8 if the size
1294  // of the base is smaller than its corresponding LLVM type.  Figure
1295  // out how many elements this base array has.
1296  llvm::ArrayType *baseArrayType = cast<llvm::ArrayType>(baseType);
1297  unsigned numBaseElements = baseArrayType->getNumElements();
1298
1299  // Fill in null data member pointers.
1300  std::vector<llvm::Constant *> baseElements(numBaseElements);
1301  FillInNullDataMemberPointers(CGM, CGM.getContext().getTypeDeclType(base),
1302                               baseElements, 0);
1303
1304  // Now go through all other elements and zero them out.
1305  if (numBaseElements) {
1306    llvm::Type *i8 = llvm::Type::getInt8Ty(CGM.getLLVMContext());
1307    llvm::Constant *i8_zero = llvm::Constant::getNullValue(i8);
1308    for (unsigned i = 0; i != numBaseElements; ++i) {
1309      if (!baseElements[i])
1310        baseElements[i] = i8_zero;
1311    }
1312  }
1313
1314  return llvm::ConstantArray::get(baseArrayType, baseElements);
1315}
1316
1317llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
1318  if (getTypes().isZeroInitializable(T))
1319    return llvm::Constant::getNullValue(getTypes().ConvertTypeForMem(T));
1320
1321  if (const ConstantArrayType *CAT = Context.getAsConstantArrayType(T)) {
1322
1323    QualType ElementTy = CAT->getElementType();
1324
1325    llvm::Constant *Element = EmitNullConstant(ElementTy);
1326    unsigned NumElements = CAT->getSize().getZExtValue();
1327    std::vector<llvm::Constant *> Array(NumElements);
1328    for (unsigned i = 0; i != NumElements; ++i)
1329      Array[i] = Element;
1330
1331    llvm::ArrayType *ATy =
1332      cast<llvm::ArrayType>(getTypes().ConvertTypeForMem(T));
1333    return llvm::ConstantArray::get(ATy, Array);
1334  }
1335
1336  if (const RecordType *RT = T->getAs<RecordType>()) {
1337    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
1338    return ::EmitNullConstant(*this, RD, /*complete object*/ true);
1339  }
1340
1341  assert(T->isMemberPointerType() && "Should only see member pointers here!");
1342  assert(!T->getAs<MemberPointerType>()->getPointeeType()->isFunctionType() &&
1343         "Should only see pointers to data members here!");
1344
1345  // Itanium C++ ABI 2.3:
1346  //   A NULL pointer is represented as -1.
1347  return getCXXABI().EmitNullMemberPointer(T->castAs<MemberPointerType>());
1348}
1349
1350llvm::Constant *
1351CodeGenModule::EmitNullConstantForBase(const CXXRecordDecl *Record) {
1352  return ::EmitNullConstant(*this, Record, false);
1353}
1354