CGExprConstant.cpp revision eb2d1f1c88836bd5382e5d7aa8f6b85148a88b27 
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 =
147    Field->getBitWidth()->EvaluateAsInt(Context).getZExtValue();
148
149  llvm::APInt FieldValue = CI->getValue();
150
151  // Promote the size of FieldValue if necessary
152  // FIXME: This should never occur, but currently it can because initializer
153  // constants are cast to bool, and because clang is not enforcing bitfield
154  // width limits.
155  if (FieldSize > FieldValue.getBitWidth())
156    FieldValue = FieldValue.zext(FieldSize);
157
158  // Truncate the size of FieldValue to the bit field size.
159  if (FieldSize < FieldValue.getBitWidth())
160    FieldValue = FieldValue.trunc(FieldSize);
161
162  NextFieldOffsetInBits = Context.toBits(NextFieldOffsetInChars);
163  if (FieldOffset < NextFieldOffsetInBits) {
164    // Either part of the field or the entire field can go into the previous
165    // byte.
166    assert(!Elements.empty() && "Elements can't be empty!");
167
168    unsigned BitsInPreviousByte = NextFieldOffsetInBits - FieldOffset;
169
170    bool FitsCompletelyInPreviousByte =
171      BitsInPreviousByte >= FieldValue.getBitWidth();
172
173    llvm::APInt Tmp = FieldValue;
174
175    if (!FitsCompletelyInPreviousByte) {
176      unsigned NewFieldWidth = FieldSize - BitsInPreviousByte;
177
178      if (CGM.getTargetData().isBigEndian()) {
179        Tmp = Tmp.lshr(NewFieldWidth);
180        Tmp = Tmp.trunc(BitsInPreviousByte);
181
182        // We want the remaining high bits.
183        FieldValue = FieldValue.trunc(NewFieldWidth);
184      } else {
185        Tmp = Tmp.trunc(BitsInPreviousByte);
186
187        // We want the remaining low bits.
188        FieldValue = FieldValue.lshr(BitsInPreviousByte);
189        FieldValue = FieldValue.trunc(NewFieldWidth);
190      }
191    }
192
193    Tmp = Tmp.zext(CharWidth);
194    if (CGM.getTargetData().isBigEndian()) {
195      if (FitsCompletelyInPreviousByte)
196        Tmp = Tmp.shl(BitsInPreviousByte - FieldValue.getBitWidth());
197    } else {
198      Tmp = Tmp.shl(CharWidth - BitsInPreviousByte);
199    }
200
201    // 'or' in the bits that go into the previous byte.
202    llvm::Value *LastElt = Elements.back();
203    if (llvm::ConstantInt *Val = dyn_cast<llvm::ConstantInt>(LastElt))
204      Tmp |= Val->getValue();
205    else {
206      assert(isa<llvm::UndefValue>(LastElt));
207      // If there is an undef field that we're adding to, it can either be a
208      // scalar undef (in which case, we just replace it with our field) or it
209      // is an array.  If it is an array, we have to pull one byte off the
210      // array so that the other undef bytes stay around.
211      if (!isa<llvm::IntegerType>(LastElt->getType())) {
212        // The undef padding will be a multibyte array, create a new smaller
213        // padding and then an hole for our i8 to get plopped into.
214        assert(isa<llvm::ArrayType>(LastElt->getType()) &&
215               "Expected array padding of undefs");
216        llvm::ArrayType *AT = cast<llvm::ArrayType>(LastElt->getType());
217        assert(AT->getElementType()->isIntegerTy(CharWidth) &&
218               AT->getNumElements() != 0 &&
219               "Expected non-empty array padding of undefs");
220
221        // Remove the padding array.
222        NextFieldOffsetInChars -= CharUnits::fromQuantity(AT->getNumElements());
223        Elements.pop_back();
224
225        // Add the padding back in two chunks.
226        AppendPadding(CharUnits::fromQuantity(AT->getNumElements()-1));
227        AppendPadding(CharUnits::One());
228        assert(isa<llvm::UndefValue>(Elements.back()) &&
229               Elements.back()->getType()->isIntegerTy(CharWidth) &&
230               "Padding addition didn't work right");
231      }
232    }
233
234    Elements.back() = llvm::ConstantInt::get(CGM.getLLVMContext(), Tmp);
235
236    if (FitsCompletelyInPreviousByte)
237      return;
238  }
239
240  while (FieldValue.getBitWidth() > CharWidth) {
241    llvm::APInt Tmp;
242
243    if (CGM.getTargetData().isBigEndian()) {
244      // We want the high bits.
245      Tmp =
246        FieldValue.lshr(FieldValue.getBitWidth() - CharWidth).trunc(CharWidth);
247    } else {
248      // We want the low bits.
249      Tmp = FieldValue.trunc(CharWidth);
250
251      FieldValue = FieldValue.lshr(CharWidth);
252    }
253
254    Elements.push_back(llvm::ConstantInt::get(CGM.getLLVMContext(), Tmp));
255    ++NextFieldOffsetInChars;
256
257    FieldValue = FieldValue.trunc(FieldValue.getBitWidth() - CharWidth);
258  }
259
260  assert(FieldValue.getBitWidth() > 0 &&
261         "Should have at least one bit left!");
262  assert(FieldValue.getBitWidth() <= CharWidth &&
263         "Should not have more than a byte left!");
264
265  if (FieldValue.getBitWidth() < CharWidth) {
266    if (CGM.getTargetData().isBigEndian()) {
267      unsigned BitWidth = FieldValue.getBitWidth();
268
269      FieldValue = FieldValue.zext(CharWidth) << (CharWidth - BitWidth);
270    } else
271      FieldValue = FieldValue.zext(CharWidth);
272  }
273
274  // Append the last element.
275  Elements.push_back(llvm::ConstantInt::get(CGM.getLLVMContext(),
276                                            FieldValue));
277  ++NextFieldOffsetInChars;
278}
279
280void ConstStructBuilder::AppendPadding(CharUnits PadSize) {
281  if (PadSize.isZero())
282    return;
283
284  llvm::Type *Ty = llvm::Type::getInt8Ty(CGM.getLLVMContext());
285  if (PadSize > CharUnits::One())
286    Ty = llvm::ArrayType::get(Ty, PadSize.getQuantity());
287
288  llvm::Constant *C = llvm::UndefValue::get(Ty);
289  Elements.push_back(C);
290  assert(getAlignment(C) == CharUnits::One() &&
291         "Padding must have 1 byte alignment!");
292
293  NextFieldOffsetInChars += getSizeInChars(C);
294}
295
296void ConstStructBuilder::AppendTailPadding(CharUnits RecordSize) {
297  assert(NextFieldOffsetInChars <= RecordSize &&
298         "Size mismatch!");
299
300  AppendPadding(RecordSize - NextFieldOffsetInChars);
301}
302
303void ConstStructBuilder::ConvertStructToPacked() {
304  std::vector<llvm::Constant *> PackedElements;
305  CharUnits ElementOffsetInChars = CharUnits::Zero();
306
307  for (unsigned i = 0, e = Elements.size(); i != e; ++i) {
308    llvm::Constant *C = Elements[i];
309
310    CharUnits ElementAlign = CharUnits::fromQuantity(
311      CGM.getTargetData().getABITypeAlignment(C->getType()));
312    CharUnits AlignedElementOffsetInChars =
313      ElementOffsetInChars.RoundUpToAlignment(ElementAlign);
314
315    if (AlignedElementOffsetInChars > ElementOffsetInChars) {
316      // We need some padding.
317      CharUnits NumChars =
318        AlignedElementOffsetInChars - ElementOffsetInChars;
319
320      llvm::Type *Ty = llvm::Type::getInt8Ty(CGM.getLLVMContext());
321      if (NumChars > CharUnits::One())
322        Ty = llvm::ArrayType::get(Ty, NumChars.getQuantity());
323
324      llvm::Constant *Padding = llvm::UndefValue::get(Ty);
325      PackedElements.push_back(Padding);
326      ElementOffsetInChars += getSizeInChars(Padding);
327    }
328
329    PackedElements.push_back(C);
330    ElementOffsetInChars += getSizeInChars(C);
331  }
332
333  assert(ElementOffsetInChars == NextFieldOffsetInChars &&
334         "Packing the struct changed its size!");
335
336  Elements = PackedElements;
337  LLVMStructAlignment = CharUnits::One();
338  Packed = true;
339}
340
341bool ConstStructBuilder::Build(InitListExpr *ILE) {
342  RecordDecl *RD = ILE->getType()->getAs<RecordType>()->getDecl();
343  const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
344
345  unsigned FieldNo = 0;
346  unsigned ElementNo = 0;
347  const FieldDecl *LastFD = 0;
348  bool IsMsStruct = RD->hasAttr<MsStructAttr>();
349
350  for (RecordDecl::field_iterator Field = RD->field_begin(),
351       FieldEnd = RD->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
352    if (IsMsStruct) {
353      // Zero-length bitfields following non-bitfield members are
354      // ignored:
355      if (CGM.getContext().ZeroBitfieldFollowsNonBitfield((*Field), LastFD)) {
356        --FieldNo;
357        continue;
358      }
359      LastFD = (*Field);
360    }
361
362    // If this is a union, skip all the fields that aren't being initialized.
363    if (RD->isUnion() && ILE->getInitializedFieldInUnion() != *Field)
364      continue;
365
366    // Don't emit anonymous bitfields, they just affect layout.
367    if (Field->isUnnamedBitfield()) {
368      LastFD = (*Field);
369      continue;
370    }
371
372    // Get the initializer.  A struct can include fields without initializers,
373    // we just use explicit null values for them.
374    llvm::Constant *EltInit;
375    if (ElementNo < ILE->getNumInits())
376      EltInit = CGM.EmitConstantExpr(ILE->getInit(ElementNo++),
377                                     Field->getType(), CGF);
378    else
379      EltInit = CGM.EmitNullConstant(Field->getType());
380
381    if (!EltInit)
382      return false;
383
384    if (!Field->isBitField()) {
385      // Handle non-bitfield members.
386      if (!AppendField(*Field, Layout.getFieldOffset(FieldNo), EltInit))
387        return false;
388    } else {
389      // Otherwise we have a bitfield.
390      AppendBitField(*Field, Layout.getFieldOffset(FieldNo),
391                     cast<llvm::ConstantInt>(EltInit));
392    }
393  }
394
395  CharUnits LayoutSizeInChars = Layout.getSize();
396
397  if (NextFieldOffsetInChars > LayoutSizeInChars) {
398    // If the struct is bigger than the size of the record type,
399    // we must have a flexible array member at the end.
400    assert(RD->hasFlexibleArrayMember() &&
401           "Must have flexible array member if struct is bigger than type!");
402
403    // No tail padding is necessary.
404    return true;
405  }
406
407  CharUnits LLVMSizeInChars =
408    NextFieldOffsetInChars.RoundUpToAlignment(LLVMStructAlignment);
409
410  // Check if we need to convert the struct to a packed struct.
411  if (NextFieldOffsetInChars <= LayoutSizeInChars &&
412      LLVMSizeInChars > LayoutSizeInChars) {
413    assert(!Packed && "Size mismatch!");
414
415    ConvertStructToPacked();
416    assert(NextFieldOffsetInChars <= LayoutSizeInChars &&
417           "Converting to packed did not help!");
418  }
419
420  // Append tail padding if necessary.
421  AppendTailPadding(LayoutSizeInChars);
422
423  assert(LayoutSizeInChars == NextFieldOffsetInChars &&
424         "Tail padding mismatch!");
425
426  return true;
427}
428
429llvm::Constant *ConstStructBuilder::
430  BuildStruct(CodeGenModule &CGM, CodeGenFunction *CGF, InitListExpr *ILE) {
431  ConstStructBuilder Builder(CGM, CGF);
432
433  if (!Builder.Build(ILE))
434    return 0;
435
436  // Pick the type to use.  If the type is layout identical to the ConvertType
437  // type then use it, otherwise use whatever the builder produced for us.
438  llvm::StructType *STy =
439      llvm::ConstantStruct::getTypeForElements(CGM.getLLVMContext(),
440                                               Builder.Elements,Builder.Packed);
441  llvm::Type *ILETy = CGM.getTypes().ConvertType(ILE->getType());
442  if (llvm::StructType *ILESTy = dyn_cast<llvm::StructType>(ILETy)) {
443    if (ILESTy->isLayoutIdentical(STy))
444      STy = ILESTy;
445  }
446
447  llvm::Constant *Result =
448    llvm::ConstantStruct::get(STy, Builder.Elements);
449
450  assert(Builder.NextFieldOffsetInChars.RoundUpToAlignment(
451           Builder.getAlignment(Result)) ==
452         Builder.getSizeInChars(Result) && "Size mismatch!");
453
454  return Result;
455}
456
457
458//===----------------------------------------------------------------------===//
459//                             ConstExprEmitter
460//===----------------------------------------------------------------------===//
461
462class ConstExprEmitter :
463  public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
464  CodeGenModule &CGM;
465  CodeGenFunction *CGF;
466  llvm::LLVMContext &VMContext;
467public:
468  ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
469    : CGM(cgm), CGF(cgf), VMContext(cgm.getLLVMContext()) {
470  }
471
472  //===--------------------------------------------------------------------===//
473  //                            Visitor Methods
474  //===--------------------------------------------------------------------===//
475
476  llvm::Constant *VisitStmt(Stmt *S) {
477    return 0;
478  }
479
480  llvm::Constant *VisitParenExpr(ParenExpr *PE) {
481    return Visit(PE->getSubExpr());
482  }
483
484  llvm::Constant *
485  VisitSubstNonTypeTemplateParmExpr(SubstNonTypeTemplateParmExpr *PE) {
486    return Visit(PE->getReplacement());
487  }
488
489  llvm::Constant *VisitGenericSelectionExpr(GenericSelectionExpr *GE) {
490    return Visit(GE->getResultExpr());
491  }
492
493  llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
494    return Visit(E->getInitializer());
495  }
496
497  llvm::Constant *VisitUnaryAddrOf(UnaryOperator *E) {
498    if (E->getType()->isMemberPointerType())
499      return CGM.getMemberPointerConstant(E);
500
501    return 0;
502  }
503
504  llvm::Constant *VisitBinSub(BinaryOperator *E) {
505    // This must be a pointer/pointer subtraction.  This only happens for
506    // address of label.
507    if (!isa<AddrLabelExpr>(E->getLHS()->IgnoreParenNoopCasts(CGM.getContext())) ||
508       !isa<AddrLabelExpr>(E->getRHS()->IgnoreParenNoopCasts(CGM.getContext())))
509      return 0;
510
511    llvm::Constant *LHS = CGM.EmitConstantExpr(E->getLHS(),
512                                               E->getLHS()->getType(), CGF);
513    llvm::Constant *RHS = CGM.EmitConstantExpr(E->getRHS(),
514                                               E->getRHS()->getType(), CGF);
515
516    llvm::Type *ResultType = ConvertType(E->getType());
517    LHS = llvm::ConstantExpr::getPtrToInt(LHS, ResultType);
518    RHS = llvm::ConstantExpr::getPtrToInt(RHS, ResultType);
519
520    // No need to divide by element size, since addr of label is always void*,
521    // which has size 1 in GNUish.
522    return llvm::ConstantExpr::getSub(LHS, RHS);
523  }
524
525  llvm::Constant *VisitCastExpr(CastExpr* E) {
526    Expr *subExpr = E->getSubExpr();
527    llvm::Constant *C = CGM.EmitConstantExpr(subExpr, subExpr->getType(), CGF);
528    if (!C) return 0;
529
530    llvm::Type *destType = ConvertType(E->getType());
531
532    switch (E->getCastKind()) {
533    case CK_ToUnion: {
534      // GCC cast to union extension
535      assert(E->getType()->isUnionType() &&
536             "Destination type is not union type!");
537
538      // Build a struct with the union sub-element as the first member,
539      // and padded to the appropriate size
540      std::vector<llvm::Constant*> Elts;
541      std::vector<llvm::Type*> Types;
542      Elts.push_back(C);
543      Types.push_back(C->getType());
544      unsigned CurSize = CGM.getTargetData().getTypeAllocSize(C->getType());
545      unsigned TotalSize = CGM.getTargetData().getTypeAllocSize(destType);
546
547      assert(CurSize <= TotalSize && "Union size mismatch!");
548      if (unsigned NumPadBytes = TotalSize - CurSize) {
549        llvm::Type *Ty = llvm::Type::getInt8Ty(VMContext);
550        if (NumPadBytes > 1)
551          Ty = llvm::ArrayType::get(Ty, NumPadBytes);
552
553        Elts.push_back(llvm::UndefValue::get(Ty));
554        Types.push_back(Ty);
555      }
556
557      llvm::StructType* STy =
558        llvm::StructType::get(C->getType()->getContext(), Types, false);
559      return llvm::ConstantStruct::get(STy, Elts);
560    }
561    case CK_NullToMemberPointer: {
562      const MemberPointerType *MPT = E->getType()->getAs<MemberPointerType>();
563      return CGM.getCXXABI().EmitNullMemberPointer(MPT);
564    }
565
566    case CK_DerivedToBaseMemberPointer:
567    case CK_BaseToDerivedMemberPointer:
568      return CGM.getCXXABI().EmitMemberPointerConversion(C, E);
569
570    case CK_LValueToRValue:
571    case CK_NoOp:
572      return C;
573
574    case CK_CPointerToObjCPointerCast:
575    case CK_BlockPointerToObjCPointerCast:
576    case CK_AnyPointerToBlockPointerCast:
577    case CK_LValueBitCast:
578    case CK_BitCast:
579      if (C->getType() == destType) return C;
580      return llvm::ConstantExpr::getBitCast(C, destType);
581
582    case CK_Dependent: llvm_unreachable("saw dependent cast!");
583
584    // These will never be supported.
585    case CK_ObjCObjectLValueCast:
586    case CK_GetObjCProperty:
587    case CK_ToVoid:
588    case CK_Dynamic:
589    case CK_ARCProduceObject:
590    case CK_ARCConsumeObject:
591    case CK_ARCReclaimReturnedObject:
592    case CK_ARCExtendBlockObject:
593      return 0;
594
595    // These might need to be supported for constexpr.
596    case CK_UserDefinedConversion:
597    case CK_ConstructorConversion:
598      return 0;
599
600    // These should eventually be supported.
601    case CK_ArrayToPointerDecay:
602    case CK_FunctionToPointerDecay:
603    case CK_BaseToDerived:
604    case CK_DerivedToBase:
605    case CK_UncheckedDerivedToBase:
606    case CK_MemberPointerToBoolean:
607    case CK_VectorSplat:
608    case CK_FloatingRealToComplex:
609    case CK_FloatingComplexToReal:
610    case CK_FloatingComplexToBoolean:
611    case CK_FloatingComplexCast:
612    case CK_FloatingComplexToIntegralComplex:
613    case CK_IntegralRealToComplex:
614    case CK_IntegralComplexToReal:
615    case CK_IntegralComplexToBoolean:
616    case CK_IntegralComplexCast:
617    case CK_IntegralComplexToFloatingComplex:
618      return 0;
619
620    case CK_PointerToIntegral:
621      if (!E->getType()->isBooleanType())
622        return llvm::ConstantExpr::getPtrToInt(C, destType);
623      // fallthrough
624
625    case CK_PointerToBoolean:
626      return llvm::ConstantExpr::getICmp(llvm::CmpInst::ICMP_EQ, C,
627        llvm::ConstantPointerNull::get(cast<llvm::PointerType>(C->getType())));
628
629    case CK_NullToPointer:
630      return llvm::ConstantPointerNull::get(cast<llvm::PointerType>(destType));
631
632    case CK_IntegralCast: {
633      bool isSigned = subExpr->getType()->isSignedIntegerOrEnumerationType();
634      return llvm::ConstantExpr::getIntegerCast(C, destType, isSigned);
635    }
636
637    case CK_IntegralToPointer: {
638      bool isSigned = subExpr->getType()->isSignedIntegerOrEnumerationType();
639      C = llvm::ConstantExpr::getIntegerCast(C, CGM.IntPtrTy, isSigned);
640      return llvm::ConstantExpr::getIntToPtr(C, destType);
641    }
642
643    case CK_IntegralToBoolean:
644      return llvm::ConstantExpr::getICmp(llvm::CmpInst::ICMP_EQ, C,
645                             llvm::Constant::getNullValue(C->getType()));
646
647    case CK_IntegralToFloating:
648      if (subExpr->getType()->isSignedIntegerOrEnumerationType())
649        return llvm::ConstantExpr::getSIToFP(C, destType);
650      else
651        return llvm::ConstantExpr::getUIToFP(C, destType);
652
653    case CK_FloatingToIntegral:
654      if (E->getType()->isSignedIntegerOrEnumerationType())
655        return llvm::ConstantExpr::getFPToSI(C, destType);
656      else
657        return llvm::ConstantExpr::getFPToUI(C, destType);
658
659    case CK_FloatingToBoolean:
660      return llvm::ConstantExpr::getFCmp(llvm::CmpInst::FCMP_UNE, C,
661                             llvm::Constant::getNullValue(C->getType()));
662
663    case CK_FloatingCast:
664      return llvm::ConstantExpr::getFPCast(C, destType);
665    }
666    llvm_unreachable("Invalid CastKind");
667  }
668
669  llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
670    return Visit(DAE->getExpr());
671  }
672
673  llvm::Constant *VisitMaterializeTemporaryExpr(MaterializeTemporaryExpr *E) {
674    return Visit(E->GetTemporaryExpr());
675  }
676
677  llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
678    unsigned NumInitElements = ILE->getNumInits();
679    if (NumInitElements == 1 && ILE->getType() == ILE->getInit(0)->getType() &&
680        (isa<StringLiteral>(ILE->getInit(0)) ||
681         isa<ObjCEncodeExpr>(ILE->getInit(0))))
682      return Visit(ILE->getInit(0));
683
684    std::vector<llvm::Constant*> Elts;
685    llvm::ArrayType *AType =
686        cast<llvm::ArrayType>(ConvertType(ILE->getType()));
687    llvm::Type *ElemTy = AType->getElementType();
688    unsigned NumElements = AType->getNumElements();
689
690    // Initialising an array requires us to automatically
691    // initialise any elements that have not been initialised explicitly
692    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
693
694    // Copy initializer elements.
695    unsigned i = 0;
696    bool RewriteType = false;
697    for (; i < NumInitableElts; ++i) {
698      Expr *Init = ILE->getInit(i);
699      llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
700      if (!C)
701        return 0;
702      RewriteType |= (C->getType() != ElemTy);
703      Elts.push_back(C);
704    }
705
706    // Initialize remaining array elements.
707    // FIXME: This doesn't handle member pointers correctly!
708    llvm::Constant *fillC;
709    if (Expr *filler = ILE->getArrayFiller())
710      fillC = CGM.EmitConstantExpr(filler, filler->getType(), CGF);
711    else
712      fillC = llvm::Constant::getNullValue(ElemTy);
713    if (!fillC)
714      return 0;
715    RewriteType |= (fillC->getType() != ElemTy);
716    for (; i < NumElements; ++i)
717      Elts.push_back(fillC);
718
719    if (RewriteType) {
720      // FIXME: Try to avoid packing the array
721      std::vector<llvm::Type*> Types;
722      for (unsigned i = 0; i < Elts.size(); ++i)
723        Types.push_back(Elts[i]->getType());
724      llvm::StructType *SType = llvm::StructType::get(AType->getContext(),
725                                                            Types, true);
726      return llvm::ConstantStruct::get(SType, Elts);
727    }
728
729    return llvm::ConstantArray::get(AType, Elts);
730  }
731
732  llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
733    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
734  }
735
736  llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
737    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
738  }
739
740  llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
741    return CGM.EmitNullConstant(E->getType());
742  }
743
744  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
745    if (ILE->getType()->isAnyComplexType() && ILE->getNumInits() == 2) {
746      // Complex type with element initializers
747      Expr *Real = ILE->getInit(0);
748      Expr *Imag = ILE->getInit(1);
749      llvm::Constant *Complex[2];
750      Complex[0] = CGM.EmitConstantExpr(Real, Real->getType(), CGF);
751      if (!Complex[0])
752        return 0;
753      Complex[1] = CGM.EmitConstantExpr(Imag, Imag->getType(), CGF);
754      if (!Complex[1])
755        return 0;
756      llvm::StructType *STy =
757          cast<llvm::StructType>(ConvertType(ILE->getType()));
758      return llvm::ConstantStruct::get(STy, Complex);
759    }
760
761    if (ILE->getType()->isScalarType()) {
762      // We have a scalar in braces. Just use the first element.
763      if (ILE->getNumInits() > 0) {
764        Expr *Init = ILE->getInit(0);
765        return CGM.EmitConstantExpr(Init, Init->getType(), CGF);
766      }
767      return CGM.EmitNullConstant(ILE->getType());
768    }
769
770    if (ILE->getType()->isArrayType())
771      return EmitArrayInitialization(ILE);
772
773    if (ILE->getType()->isRecordType())
774      return EmitStructInitialization(ILE);
775
776    if (ILE->getType()->isUnionType())
777      return EmitUnionInitialization(ILE);
778
779    // If ILE was a constant vector, we would have handled it already.
780    if (ILE->getType()->isVectorType())
781      return 0;
782
783    llvm_unreachable("Unable to handle InitListExpr");
784  }
785
786  llvm::Constant *VisitCXXConstructExpr(CXXConstructExpr *E) {
787    if (!E->getConstructor()->isTrivial())
788      return 0;
789
790    QualType Ty = E->getType();
791
792    // FIXME: We should not have to call getBaseElementType here.
793    const RecordType *RT =
794      CGM.getContext().getBaseElementType(Ty)->getAs<RecordType>();
795    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
796
797    // If the class doesn't have a trivial destructor, we can't emit it as a
798    // constant expr.
799    if (!RD->hasTrivialDestructor())
800      return 0;
801
802    // Only copy and default constructors can be trivial.
803
804
805    if (E->getNumArgs()) {
806      assert(E->getNumArgs() == 1 && "trivial ctor with > 1 argument");
807      assert(E->getConstructor()->isCopyOrMoveConstructor() &&
808             "trivial ctor has argument but isn't a copy/move ctor");
809
810      Expr *Arg = E->getArg(0);
811      assert(CGM.getContext().hasSameUnqualifiedType(Ty, Arg->getType()) &&
812             "argument to copy ctor is of wrong type");
813
814      return Visit(Arg);
815    }
816
817    return CGM.EmitNullConstant(Ty);
818  }
819
820  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
821    assert(!E->getType()->isPointerType() && "Strings are always arrays");
822
823    // This must be a string 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    return llvm::ConstantArray::get(VMContext,
827                                    CGM.GetStringForStringLiteral(E), false);
828  }
829
830  llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
831    // This must be an @encode initializing an array in a static initializer.
832    // Don't emit it as the address of the string, emit the string data itself
833    // as an inline array.
834    std::string Str;
835    CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
836    const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
837
838    // Resize the string to the right size, adding zeros at the end, or
839    // truncating as needed.
840    Str.resize(CAT->getSize().getZExtValue(), '\0');
841    return llvm::ConstantArray::get(VMContext, Str, false);
842  }
843
844  llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
845    return Visit(E->getSubExpr());
846  }
847
848  // Utility methods
849  llvm::Type *ConvertType(QualType T) {
850    return CGM.getTypes().ConvertType(T);
851  }
852
853public:
854  llvm::Constant *EmitLValue(Expr *E) {
855    switch (E->getStmtClass()) {
856    default: break;
857    case Expr::CompoundLiteralExprClass: {
858      // Note that due to the nature of compound literals, this is guaranteed
859      // to be the only use of the variable, so we just generate it here.
860      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
861      llvm::Constant* C = Visit(CLE->getInitializer());
862      // FIXME: "Leaked" on failure.
863      if (C)
864        C = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
865                                     E->getType().isConstant(CGM.getContext()),
866                                     llvm::GlobalValue::InternalLinkage,
867                                     C, ".compoundliteral", 0, false,
868                          CGM.getContext().getTargetAddressSpace(E->getType()));
869      return C;
870    }
871    case Expr::DeclRefExprClass: {
872      ValueDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
873      if (Decl->hasAttr<WeakRefAttr>())
874        return CGM.GetWeakRefReference(Decl);
875      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
876        return CGM.GetAddrOfFunction(FD);
877      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
878        // We can never refer to a variable with local storage.
879        if (!VD->hasLocalStorage()) {
880          if (VD->isFileVarDecl() || VD->hasExternalStorage())
881            return CGM.GetAddrOfGlobalVar(VD);
882          else if (VD->isLocalVarDecl()) {
883            assert(CGF && "Can't access static local vars without CGF");
884            return CGF->GetAddrOfStaticLocalVar(VD);
885          }
886        }
887      }
888      break;
889    }
890    case Expr::StringLiteralClass:
891      return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
892    case Expr::ObjCEncodeExprClass:
893      return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
894    case Expr::ObjCStringLiteralClass: {
895      ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
896      llvm::Constant *C =
897          CGM.getObjCRuntime().GenerateConstantString(SL->getString());
898      return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
899    }
900    case Expr::PredefinedExprClass: {
901      unsigned Type = cast<PredefinedExpr>(E)->getIdentType();
902      if (CGF) {
903        LValue Res = CGF->EmitPredefinedLValue(cast<PredefinedExpr>(E));
904        return cast<llvm::Constant>(Res.getAddress());
905      } else if (Type == PredefinedExpr::PrettyFunction) {
906        return CGM.GetAddrOfConstantCString("top level", ".tmp");
907      }
908
909      return CGM.GetAddrOfConstantCString("", ".tmp");
910    }
911    case Expr::AddrLabelExprClass: {
912      assert(CGF && "Invalid address of label expression outside function.");
913      llvm::Constant *Ptr =
914        CGF->GetAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
915      return llvm::ConstantExpr::getBitCast(Ptr, ConvertType(E->getType()));
916    }
917    case Expr::CallExprClass: {
918      CallExpr* CE = cast<CallExpr>(E);
919      unsigned builtin = CE->isBuiltinCall(CGM.getContext());
920      if (builtin !=
921            Builtin::BI__builtin___CFStringMakeConstantString &&
922          builtin !=
923            Builtin::BI__builtin___NSStringMakeConstantString)
924        break;
925      const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
926      const StringLiteral *Literal = cast<StringLiteral>(Arg);
927      if (builtin ==
928            Builtin::BI__builtin___NSStringMakeConstantString) {
929        return CGM.getObjCRuntime().GenerateConstantString(Literal);
930      }
931      // FIXME: need to deal with UCN conversion issues.
932      return CGM.GetAddrOfConstantCFString(Literal);
933    }
934    case Expr::BlockExprClass: {
935      std::string FunctionName;
936      if (CGF)
937        FunctionName = CGF->CurFn->getName();
938      else
939        FunctionName = "global";
940
941      return CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
942    }
943    }
944
945    return 0;
946  }
947};
948
949}  // end anonymous namespace.
950
951llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
952                                                QualType DestType,
953                                                CodeGenFunction *CGF) {
954  Expr::EvalResult Result;
955
956  bool Success = false;
957
958  if (DestType->isReferenceType())
959    Success = E->EvaluateAsLValue(Result, Context);
960  else
961    Success = E->Evaluate(Result, Context);
962
963  if (Success && !Result.HasSideEffects) {
964    switch (Result.Val.getKind()) {
965    case APValue::Uninitialized:
966      llvm_unreachable("Constant expressions should be initialized.");
967    case APValue::LValue: {
968      llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
969      llvm::Constant *Offset =
970        llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext),
971                               Result.Val.getLValueOffset().getQuantity());
972
973      llvm::Constant *C;
974      if (const Expr *LVBase = Result.Val.getLValueBase()) {
975        C = ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
976
977        // Apply offset if necessary.
978        if (!Offset->isNullValue()) {
979          llvm::Type *Type = llvm::Type::getInt8PtrTy(VMContext);
980          llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
981          Casted = llvm::ConstantExpr::getGetElementPtr(Casted, Offset);
982          C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
983        }
984
985        // Convert to the appropriate type; this could be an lvalue for
986        // an integer.
987        if (isa<llvm::PointerType>(DestTy))
988          return llvm::ConstantExpr::getBitCast(C, DestTy);
989
990        return llvm::ConstantExpr::getPtrToInt(C, DestTy);
991      } else {
992        C = Offset;
993
994        // Convert to the appropriate type; this could be an lvalue for
995        // an integer.
996        if (isa<llvm::PointerType>(DestTy))
997          return llvm::ConstantExpr::getIntToPtr(C, DestTy);
998
999        // If the types don't match this should only be a truncate.
1000        if (C->getType() != DestTy)
1001          return llvm::ConstantExpr::getTrunc(C, DestTy);
1002
1003        return C;
1004      }
1005    }
1006    case APValue::Int: {
1007      llvm::Constant *C = llvm::ConstantInt::get(VMContext,
1008                                                 Result.Val.getInt());
1009
1010      if (C->getType()->isIntegerTy(1)) {
1011        llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
1012        C = llvm::ConstantExpr::getZExt(C, BoolTy);
1013      }
1014      return C;
1015    }
1016    case APValue::ComplexInt: {
1017      llvm::Constant *Complex[2];
1018
1019      Complex[0] = llvm::ConstantInt::get(VMContext,
1020                                          Result.Val.getComplexIntReal());
1021      Complex[1] = llvm::ConstantInt::get(VMContext,
1022                                          Result.Val.getComplexIntImag());
1023
1024      // FIXME: the target may want to specify that this is packed.
1025      llvm::StructType *STy = llvm::StructType::get(Complex[0]->getType(),
1026                                                    Complex[1]->getType(),
1027                                                    NULL);
1028      return llvm::ConstantStruct::get(STy, Complex);
1029    }
1030    case APValue::Float:
1031      return llvm::ConstantFP::get(VMContext, Result.Val.getFloat());
1032    case APValue::ComplexFloat: {
1033      llvm::Constant *Complex[2];
1034
1035      Complex[0] = llvm::ConstantFP::get(VMContext,
1036                                         Result.Val.getComplexFloatReal());
1037      Complex[1] = llvm::ConstantFP::get(VMContext,
1038                                         Result.Val.getComplexFloatImag());
1039
1040      // FIXME: the target may want to specify that this is packed.
1041      llvm::StructType *STy = llvm::StructType::get(Complex[0]->getType(),
1042                                                    Complex[1]->getType(),
1043                                                    NULL);
1044      return llvm::ConstantStruct::get(STy, Complex);
1045    }
1046    case APValue::Vector: {
1047      SmallVector<llvm::Constant *, 4> Inits;
1048      unsigned NumElts = Result.Val.getVectorLength();
1049
1050      if (Context.getLangOptions().AltiVec &&
1051          isa<CastExpr>(E) &&
1052          cast<CastExpr>(E)->getCastKind() == CK_VectorSplat) {
1053        // AltiVec vector initialization with a single literal
1054        APValue &Elt = Result.Val.getVectorElt(0);
1055
1056        llvm::Constant* InitValue = Elt.isInt()
1057          ? cast<llvm::Constant>
1058              (llvm::ConstantInt::get(VMContext, Elt.getInt()))
1059          : cast<llvm::Constant>
1060              (llvm::ConstantFP::get(VMContext, Elt.getFloat()));
1061
1062        for (unsigned i = 0; i != NumElts; ++i)
1063          Inits.push_back(InitValue);
1064
1065      } else {
1066        for (unsigned i = 0; i != NumElts; ++i) {
1067          APValue &Elt = Result.Val.getVectorElt(i);
1068          if (Elt.isInt())
1069            Inits.push_back(llvm::ConstantInt::get(VMContext, Elt.getInt()));
1070          else
1071            Inits.push_back(llvm::ConstantFP::get(VMContext, Elt.getFloat()));
1072        }
1073      }
1074      return llvm::ConstantVector::get(Inits);
1075    }
1076    }
1077  }
1078
1079  llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
1080  if (C && C->getType()->isIntegerTy(1)) {
1081    llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
1082    C = llvm::ConstantExpr::getZExt(C, BoolTy);
1083  }
1084  return C;
1085}
1086
1087static uint64_t getFieldOffset(ASTContext &C, const FieldDecl *field) {
1088  const ASTRecordLayout &layout = C.getASTRecordLayout(field->getParent());
1089  return layout.getFieldOffset(field->getFieldIndex());
1090}
1091
1092llvm::Constant *
1093CodeGenModule::getMemberPointerConstant(const UnaryOperator *uo) {
1094  // Member pointer constants always have a very particular form.
1095  const MemberPointerType *type = cast<MemberPointerType>(uo->getType());
1096  const ValueDecl *decl = cast<DeclRefExpr>(uo->getSubExpr())->getDecl();
1097
1098  // A member function pointer.
1099  if (const CXXMethodDecl *method = dyn_cast<CXXMethodDecl>(decl))
1100    return getCXXABI().EmitMemberPointer(method);
1101
1102  // Otherwise, a member data pointer.
1103  uint64_t fieldOffset;
1104  if (const FieldDecl *field = dyn_cast<FieldDecl>(decl))
1105    fieldOffset = getFieldOffset(getContext(), field);
1106  else {
1107    const IndirectFieldDecl *ifield = cast<IndirectFieldDecl>(decl);
1108
1109    fieldOffset = 0;
1110    for (IndirectFieldDecl::chain_iterator ci = ifield->chain_begin(),
1111           ce = ifield->chain_end(); ci != ce; ++ci)
1112      fieldOffset += getFieldOffset(getContext(), cast<FieldDecl>(*ci));
1113  }
1114
1115  CharUnits chars = getContext().toCharUnitsFromBits((int64_t) fieldOffset);
1116  return getCXXABI().EmitMemberDataPointer(type, chars);
1117}
1118
1119static void
1120FillInNullDataMemberPointers(CodeGenModule &CGM, QualType T,
1121                             std::vector<llvm::Constant *> &Elements,
1122                             uint64_t StartOffset) {
1123  assert(StartOffset % CGM.getContext().getCharWidth() == 0 &&
1124         "StartOffset not byte aligned!");
1125
1126  if (CGM.getTypes().isZeroInitializable(T))
1127    return;
1128
1129  if (const ConstantArrayType *CAT =
1130        CGM.getContext().getAsConstantArrayType(T)) {
1131    QualType ElementTy = CAT->getElementType();
1132    uint64_t ElementSize = CGM.getContext().getTypeSize(ElementTy);
1133
1134    for (uint64_t I = 0, E = CAT->getSize().getZExtValue(); I != E; ++I) {
1135      FillInNullDataMemberPointers(CGM, ElementTy, Elements,
1136                                   StartOffset + I * ElementSize);
1137    }
1138  } else if (const RecordType *RT = T->getAs<RecordType>()) {
1139    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
1140    const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
1141
1142    // Go through all bases and fill in any null pointer to data members.
1143    for (CXXRecordDecl::base_class_const_iterator I = RD->bases_begin(),
1144         E = RD->bases_end(); I != E; ++I) {
1145      if (I->isVirtual()) {
1146        // Ignore virtual bases.
1147        continue;
1148      }
1149
1150      const CXXRecordDecl *BaseDecl =
1151      cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());
1152
1153      // Ignore empty bases.
1154      if (BaseDecl->isEmpty())
1155        continue;
1156
1157      // Ignore bases that don't have any pointer to data members.
1158      if (CGM.getTypes().isZeroInitializable(BaseDecl))
1159        continue;
1160
1161      uint64_t BaseOffset = Layout.getBaseClassOffsetInBits(BaseDecl);
1162      FillInNullDataMemberPointers(CGM, I->getType(),
1163                                   Elements, StartOffset + BaseOffset);
1164    }
1165
1166    // Visit all fields.
1167    unsigned FieldNo = 0;
1168    for (RecordDecl::field_iterator I = RD->field_begin(),
1169         E = RD->field_end(); I != E; ++I, ++FieldNo) {
1170      QualType FieldType = I->getType();
1171
1172      if (CGM.getTypes().isZeroInitializable(FieldType))
1173        continue;
1174
1175      uint64_t FieldOffset = StartOffset + Layout.getFieldOffset(FieldNo);
1176      FillInNullDataMemberPointers(CGM, FieldType, Elements, FieldOffset);
1177    }
1178  } else {
1179    assert(T->isMemberPointerType() && "Should only see member pointers here!");
1180    assert(!T->getAs<MemberPointerType>()->getPointeeType()->isFunctionType() &&
1181           "Should only see pointers to data members here!");
1182
1183    CharUnits StartIndex = CGM.getContext().toCharUnitsFromBits(StartOffset);
1184    CharUnits EndIndex = StartIndex + CGM.getContext().getTypeSizeInChars(T);
1185
1186    // FIXME: hardcodes Itanium member pointer representation!
1187    llvm::Constant *NegativeOne =
1188      llvm::ConstantInt::get(llvm::Type::getInt8Ty(CGM.getLLVMContext()),
1189                             -1ULL, /*isSigned*/true);
1190
1191    // Fill in the null data member pointer.
1192    for (CharUnits I = StartIndex; I != EndIndex; ++I)
1193      Elements[I.getQuantity()] = NegativeOne;
1194  }
1195}
1196
1197static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
1198                                               llvm::Type *baseType,
1199                                               const CXXRecordDecl *base);
1200
1201static llvm::Constant *EmitNullConstant(CodeGenModule &CGM,
1202                                        const CXXRecordDecl *record,
1203                                        bool asCompleteObject) {
1204  const CGRecordLayout &layout = CGM.getTypes().getCGRecordLayout(record);
1205  llvm::StructType *structure =
1206    (asCompleteObject ? layout.getLLVMType()
1207                      : layout.getBaseSubobjectLLVMType());
1208
1209  unsigned numElements = structure->getNumElements();
1210  std::vector<llvm::Constant *> elements(numElements);
1211
1212  // Fill in all the bases.
1213  for (CXXRecordDecl::base_class_const_iterator
1214         I = record->bases_begin(), E = record->bases_end(); I != E; ++I) {
1215    if (I->isVirtual()) {
1216      // Ignore virtual bases; if we're laying out for a complete
1217      // object, we'll lay these out later.
1218      continue;
1219    }
1220
1221    const CXXRecordDecl *base =
1222      cast<CXXRecordDecl>(I->getType()->castAs<RecordType>()->getDecl());
1223
1224    // Ignore empty bases.
1225    if (base->isEmpty())
1226      continue;
1227
1228    unsigned fieldIndex = layout.getNonVirtualBaseLLVMFieldNo(base);
1229    llvm::Type *baseType = structure->getElementType(fieldIndex);
1230    elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
1231  }
1232
1233  // Fill in all the fields.
1234  for (RecordDecl::field_iterator I = record->field_begin(),
1235         E = record->field_end(); I != E; ++I) {
1236    const FieldDecl *field = *I;
1237
1238    // Ignore bit fields.
1239    if (field->isBitField())
1240      continue;
1241
1242    unsigned fieldIndex = layout.getLLVMFieldNo(field);
1243    elements[fieldIndex] = CGM.EmitNullConstant(field->getType());
1244  }
1245
1246  // Fill in the virtual bases, if we're working with the complete object.
1247  if (asCompleteObject) {
1248    for (CXXRecordDecl::base_class_const_iterator
1249           I = record->vbases_begin(), E = record->vbases_end(); I != E; ++I) {
1250      const CXXRecordDecl *base =
1251        cast<CXXRecordDecl>(I->getType()->castAs<RecordType>()->getDecl());
1252
1253      // Ignore empty bases.
1254      if (base->isEmpty())
1255        continue;
1256
1257      unsigned fieldIndex = layout.getVirtualBaseIndex(base);
1258
1259      // We might have already laid this field out.
1260      if (elements[fieldIndex]) continue;
1261
1262      llvm::Type *baseType = structure->getElementType(fieldIndex);
1263      elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
1264    }
1265  }
1266
1267  // Now go through all other fields and zero them out.
1268  for (unsigned i = 0; i != numElements; ++i) {
1269    if (!elements[i])
1270      elements[i] = llvm::Constant::getNullValue(structure->getElementType(i));
1271  }
1272
1273  return llvm::ConstantStruct::get(structure, elements);
1274}
1275
1276/// Emit the null constant for a base subobject.
1277static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
1278                                               llvm::Type *baseType,
1279                                               const CXXRecordDecl *base) {
1280  const CGRecordLayout &baseLayout = CGM.getTypes().getCGRecordLayout(base);
1281
1282  // Just zero out bases that don't have any pointer to data members.
1283  if (baseLayout.isZeroInitializableAsBase())
1284    return llvm::Constant::getNullValue(baseType);
1285
1286  // If the base type is a struct, we can just use its null constant.
1287  if (isa<llvm::StructType>(baseType)) {
1288    return EmitNullConstant(CGM, base, /*complete*/ false);
1289  }
1290
1291  // Otherwise, some bases are represented as arrays of i8 if the size
1292  // of the base is smaller than its corresponding LLVM type.  Figure
1293  // out how many elements this base array has.
1294  llvm::ArrayType *baseArrayType = cast<llvm::ArrayType>(baseType);
1295  unsigned numBaseElements = baseArrayType->getNumElements();
1296
1297  // Fill in null data member pointers.
1298  std::vector<llvm::Constant *> baseElements(numBaseElements);
1299  FillInNullDataMemberPointers(CGM, CGM.getContext().getTypeDeclType(base),
1300                               baseElements, 0);
1301
1302  // Now go through all other elements and zero them out.
1303  if (numBaseElements) {
1304    llvm::Type *i8 = llvm::Type::getInt8Ty(CGM.getLLVMContext());
1305    llvm::Constant *i8_zero = llvm::Constant::getNullValue(i8);
1306    for (unsigned i = 0; i != numBaseElements; ++i) {
1307      if (!baseElements[i])
1308        baseElements[i] = i8_zero;
1309    }
1310  }
1311
1312  return llvm::ConstantArray::get(baseArrayType, baseElements);
1313}
1314
1315llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
1316  if (getTypes().isZeroInitializable(T))
1317    return llvm::Constant::getNullValue(getTypes().ConvertTypeForMem(T));
1318
1319  if (const ConstantArrayType *CAT = Context.getAsConstantArrayType(T)) {
1320
1321    QualType ElementTy = CAT->getElementType();
1322
1323    llvm::Constant *Element = EmitNullConstant(ElementTy);
1324    unsigned NumElements = CAT->getSize().getZExtValue();
1325    std::vector<llvm::Constant *> Array(NumElements);
1326    for (unsigned i = 0; i != NumElements; ++i)
1327      Array[i] = Element;
1328
1329    llvm::ArrayType *ATy =
1330      cast<llvm::ArrayType>(getTypes().ConvertTypeForMem(T));
1331    return llvm::ConstantArray::get(ATy, Array);
1332  }
1333
1334  if (const RecordType *RT = T->getAs<RecordType>()) {
1335    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
1336    return ::EmitNullConstant(*this, RD, /*complete object*/ true);
1337  }
1338
1339  assert(T->isMemberPointerType() && "Should only see member pointers here!");
1340  assert(!T->getAs<MemberPointerType>()->getPointeeType()->isFunctionType() &&
1341         "Should only see pointers to data members here!");
1342
1343  // Itanium C++ ABI 2.3:
1344  //   A NULL pointer is represented as -1.
1345  return getCXXABI().EmitNullMemberPointer(T->castAs<MemberPointerType>());
1346}
1347