CGExprConstant.cpp revision 4f318c080b5ea89e3f7407516fd8ed45b733b99d 
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.Target.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        const 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 += CharUnits::One();
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 += CharUnits::One();
278}
279
280void ConstStructBuilder::AppendPadding(CharUnits PadSize) {
281  if (PadSize.isZero())
282    return;
283
284  const 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      const 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  for (RecordDecl::field_iterator Field = RD->field_begin(),
348       FieldEnd = RD->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
349
350    // If this is a union, skip all the fields that aren't being initialized.
351    if (RD->isUnion() && ILE->getInitializedFieldInUnion() != *Field)
352      continue;
353
354    // Don't emit anonymous bitfields, they just affect layout.
355    if (Field->isBitField() && !Field->getIdentifier())
356      continue;
357
358    // Get the initializer.  A struct can include fields without initializers,
359    // we just use explicit null values for them.
360    llvm::Constant *EltInit;
361    if (ElementNo < ILE->getNumInits())
362      EltInit = CGM.EmitConstantExpr(ILE->getInit(ElementNo++),
363                                     Field->getType(), CGF);
364    else
365      EltInit = CGM.EmitNullConstant(Field->getType());
366
367    if (!EltInit)
368      return false;
369
370    if (!Field->isBitField()) {
371      // Handle non-bitfield members.
372      if (!AppendField(*Field, Layout.getFieldOffset(FieldNo), EltInit))
373        return false;
374    } else {
375      // Otherwise we have a bitfield.
376      AppendBitField(*Field, Layout.getFieldOffset(FieldNo),
377                     cast<llvm::ConstantInt>(EltInit));
378    }
379  }
380
381  CharUnits LayoutSizeInChars = Layout.getSize();
382
383  if (NextFieldOffsetInChars > LayoutSizeInChars) {
384    // If the struct is bigger than the size of the record type,
385    // we must have a flexible array member at the end.
386    assert(RD->hasFlexibleArrayMember() &&
387           "Must have flexible array member if struct is bigger than type!");
388
389    // No tail padding is necessary.
390    return true;
391  }
392
393  CharUnits LLVMSizeInChars =
394    NextFieldOffsetInChars.RoundUpToAlignment(LLVMStructAlignment);
395
396  // Check if we need to convert the struct to a packed struct.
397  if (NextFieldOffsetInChars <= LayoutSizeInChars &&
398      LLVMSizeInChars > LayoutSizeInChars) {
399    assert(!Packed && "Size mismatch!");
400
401    ConvertStructToPacked();
402    assert(NextFieldOffsetInChars <= LayoutSizeInChars &&
403           "Converting to packed did not help!");
404  }
405
406  // Append tail padding if necessary.
407  AppendTailPadding(LayoutSizeInChars);
408
409  assert(LayoutSizeInChars == NextFieldOffsetInChars &&
410         "Tail padding mismatch!");
411
412  return true;
413}
414
415llvm::Constant *ConstStructBuilder::
416  BuildStruct(CodeGenModule &CGM, CodeGenFunction *CGF, InitListExpr *ILE) {
417  ConstStructBuilder Builder(CGM, CGF);
418
419  if (!Builder.Build(ILE))
420    return 0;
421
422  llvm::Constant *Result =
423  llvm::ConstantStruct::get(CGM.getLLVMContext(),
424                            Builder.Elements, Builder.Packed);
425
426  assert(Builder.NextFieldOffsetInChars.RoundUpToAlignment(
427           Builder.getAlignment(Result)) ==
428         Builder.getSizeInChars(Result) && "Size mismatch!");
429
430  return Result;
431}
432
433
434//===----------------------------------------------------------------------===//
435//                             ConstExprEmitter
436//===----------------------------------------------------------------------===//
437
438class ConstExprEmitter :
439  public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
440  CodeGenModule &CGM;
441  CodeGenFunction *CGF;
442  llvm::LLVMContext &VMContext;
443public:
444  ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
445    : CGM(cgm), CGF(cgf), VMContext(cgm.getLLVMContext()) {
446  }
447
448  //===--------------------------------------------------------------------===//
449  //                            Visitor Methods
450  //===--------------------------------------------------------------------===//
451
452  llvm::Constant *VisitStmt(Stmt *S) {
453    return 0;
454  }
455
456  llvm::Constant *VisitParenExpr(ParenExpr *PE) {
457    return Visit(PE->getSubExpr());
458  }
459
460  llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
461    return Visit(E->getInitializer());
462  }
463
464  llvm::Constant *VisitUnaryAddrOf(UnaryOperator *E) {
465    if (E->getType()->isMemberPointerType())
466      return CGM.getMemberPointerConstant(E);
467
468    return 0;
469  }
470
471  llvm::Constant *VisitBinSub(BinaryOperator *E) {
472    // This must be a pointer/pointer subtraction.  This only happens for
473    // address of label.
474    if (!isa<AddrLabelExpr>(E->getLHS()->IgnoreParenNoopCasts(CGM.getContext())) ||
475       !isa<AddrLabelExpr>(E->getRHS()->IgnoreParenNoopCasts(CGM.getContext())))
476      return 0;
477
478    llvm::Constant *LHS = CGM.EmitConstantExpr(E->getLHS(),
479                                               E->getLHS()->getType(), CGF);
480    llvm::Constant *RHS = CGM.EmitConstantExpr(E->getRHS(),
481                                               E->getRHS()->getType(), CGF);
482
483    const llvm::Type *ResultType = ConvertType(E->getType());
484    LHS = llvm::ConstantExpr::getPtrToInt(LHS, ResultType);
485    RHS = llvm::ConstantExpr::getPtrToInt(RHS, ResultType);
486
487    // No need to divide by element size, since addr of label is always void*,
488    // which has size 1 in GNUish.
489    return llvm::ConstantExpr::getSub(LHS, RHS);
490  }
491
492  llvm::Constant *VisitCastExpr(CastExpr* E) {
493    Expr *subExpr = E->getSubExpr();
494    llvm::Constant *C = CGM.EmitConstantExpr(subExpr, subExpr->getType(), CGF);
495    if (!C) return 0;
496
497    const llvm::Type *destType = ConvertType(E->getType());
498
499    switch (E->getCastKind()) {
500    case CK_ToUnion: {
501      // GCC cast to union extension
502      assert(E->getType()->isUnionType() &&
503             "Destination type is not union type!");
504
505      // Build a struct with the union sub-element as the first member,
506      // and padded to the appropriate size
507      std::vector<llvm::Constant*> Elts;
508      std::vector<const llvm::Type*> Types;
509      Elts.push_back(C);
510      Types.push_back(C->getType());
511      unsigned CurSize = CGM.getTargetData().getTypeAllocSize(C->getType());
512      unsigned TotalSize = CGM.getTargetData().getTypeAllocSize(destType);
513
514      assert(CurSize <= TotalSize && "Union size mismatch!");
515      if (unsigned NumPadBytes = TotalSize - CurSize) {
516        const llvm::Type *Ty = llvm::Type::getInt8Ty(VMContext);
517        if (NumPadBytes > 1)
518          Ty = llvm::ArrayType::get(Ty, NumPadBytes);
519
520        Elts.push_back(llvm::UndefValue::get(Ty));
521        Types.push_back(Ty);
522      }
523
524      llvm::StructType* STy =
525        llvm::StructType::get(C->getType()->getContext(), Types, false);
526      return llvm::ConstantStruct::get(STy, Elts);
527    }
528    case CK_NullToMemberPointer: {
529      const MemberPointerType *MPT = E->getType()->getAs<MemberPointerType>();
530      return CGM.getCXXABI().EmitNullMemberPointer(MPT);
531    }
532
533    case CK_DerivedToBaseMemberPointer:
534    case CK_BaseToDerivedMemberPointer:
535      return CGM.getCXXABI().EmitMemberPointerConversion(C, E);
536
537    case CK_LValueToRValue:
538    case CK_NoOp:
539      return C;
540
541    case CK_AnyPointerToObjCPointerCast:
542    case CK_AnyPointerToBlockPointerCast:
543    case CK_LValueBitCast:
544    case CK_BitCast:
545      if (C->getType() == destType) return C;
546      return llvm::ConstantExpr::getBitCast(C, destType);
547
548    case CK_Dependent: llvm_unreachable("saw dependent cast!");
549
550    // These will never be supported.
551    case CK_ObjCObjectLValueCast:
552    case CK_GetObjCProperty:
553    case CK_ToVoid:
554    case CK_Dynamic:
555      return 0;
556
557    // These might need to be supported for constexpr.
558    case CK_UserDefinedConversion:
559    case CK_ConstructorConversion:
560      return 0;
561
562    // These should eventually be supported.
563    case CK_ArrayToPointerDecay:
564    case CK_FunctionToPointerDecay:
565    case CK_BaseToDerived:
566    case CK_DerivedToBase:
567    case CK_UncheckedDerivedToBase:
568    case CK_MemberPointerToBoolean:
569    case CK_VectorSplat:
570    case CK_FloatingRealToComplex:
571    case CK_FloatingComplexToReal:
572    case CK_FloatingComplexToBoolean:
573    case CK_FloatingComplexCast:
574    case CK_FloatingComplexToIntegralComplex:
575    case CK_IntegralRealToComplex:
576    case CK_IntegralComplexToReal:
577    case CK_IntegralComplexToBoolean:
578    case CK_IntegralComplexCast:
579    case CK_IntegralComplexToFloatingComplex:
580      return 0;
581
582    case CK_PointerToIntegral:
583      if (!E->getType()->isBooleanType())
584        return llvm::ConstantExpr::getPtrToInt(C, destType);
585      // fallthrough
586
587    case CK_PointerToBoolean:
588      return llvm::ConstantExpr::getICmp(llvm::CmpInst::ICMP_EQ, C,
589        llvm::ConstantPointerNull::get(cast<llvm::PointerType>(C->getType())));
590
591    case CK_NullToPointer:
592      return llvm::ConstantPointerNull::get(cast<llvm::PointerType>(destType));
593
594    case CK_IntegralCast: {
595      bool isSigned = subExpr->getType()->isSignedIntegerType();
596      return llvm::ConstantExpr::getIntegerCast(C, destType, isSigned);
597    }
598
599    case CK_IntegralToPointer: {
600      bool isSigned = subExpr->getType()->isSignedIntegerType();
601      C = llvm::ConstantExpr::getIntegerCast(C, CGM.IntPtrTy, isSigned);
602      return llvm::ConstantExpr::getIntToPtr(C, destType);
603    }
604
605    case CK_IntegralToBoolean:
606      return llvm::ConstantExpr::getICmp(llvm::CmpInst::ICMP_EQ, C,
607                             llvm::Constant::getNullValue(C->getType()));
608
609    case CK_IntegralToFloating:
610      if (subExpr->getType()->isSignedIntegerType())
611        return llvm::ConstantExpr::getSIToFP(C, destType);
612      else
613        return llvm::ConstantExpr::getUIToFP(C, destType);
614
615    case CK_FloatingToIntegral:
616      if (E->getType()->isSignedIntegerType())
617        return llvm::ConstantExpr::getFPToSI(C, destType);
618      else
619        return llvm::ConstantExpr::getFPToUI(C, destType);
620
621    case CK_FloatingToBoolean:
622      return llvm::ConstantExpr::getFCmp(llvm::CmpInst::FCMP_UNE, C,
623                             llvm::Constant::getNullValue(C->getType()));
624
625    case CK_FloatingCast:
626      return llvm::ConstantExpr::getFPCast(C, destType);
627    }
628    llvm_unreachable("Invalid CastKind");
629  }
630
631  llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
632    return Visit(DAE->getExpr());
633  }
634
635  llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
636    unsigned NumInitElements = ILE->getNumInits();
637    if (NumInitElements == 1 && ILE->getType() == ILE->getInit(0)->getType() &&
638        (isa<StringLiteral>(ILE->getInit(0)) ||
639         isa<ObjCEncodeExpr>(ILE->getInit(0))))
640      return Visit(ILE->getInit(0));
641
642    std::vector<llvm::Constant*> Elts;
643    const llvm::ArrayType *AType =
644        cast<llvm::ArrayType>(ConvertType(ILE->getType()));
645    const llvm::Type *ElemTy = AType->getElementType();
646    unsigned NumElements = AType->getNumElements();
647
648    // Initialising an array requires us to automatically
649    // initialise any elements that have not been initialised explicitly
650    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
651
652    // Copy initializer elements.
653    unsigned i = 0;
654    bool RewriteType = false;
655    for (; i < NumInitableElts; ++i) {
656      Expr *Init = ILE->getInit(i);
657      llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
658      if (!C)
659        return 0;
660      RewriteType |= (C->getType() != ElemTy);
661      Elts.push_back(C);
662    }
663
664    // Initialize remaining array elements.
665    // FIXME: This doesn't handle member pointers correctly!
666    for (; i < NumElements; ++i)
667      Elts.push_back(llvm::Constant::getNullValue(ElemTy));
668
669    if (RewriteType) {
670      // FIXME: Try to avoid packing the array
671      std::vector<const llvm::Type*> Types;
672      for (unsigned i = 0; i < Elts.size(); ++i)
673        Types.push_back(Elts[i]->getType());
674      const llvm::StructType *SType = llvm::StructType::get(AType->getContext(),
675                                                            Types, true);
676      return llvm::ConstantStruct::get(SType, Elts);
677    }
678
679    return llvm::ConstantArray::get(AType, Elts);
680  }
681
682  llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
683    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
684  }
685
686  llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
687    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
688  }
689
690  llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
691    return CGM.EmitNullConstant(E->getType());
692  }
693
694  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
695    if (ILE->getType()->isScalarType()) {
696      // We have a scalar in braces. Just use the first element.
697      if (ILE->getNumInits() > 0) {
698        Expr *Init = ILE->getInit(0);
699        return CGM.EmitConstantExpr(Init, Init->getType(), CGF);
700      }
701      return CGM.EmitNullConstant(ILE->getType());
702    }
703
704    if (ILE->getType()->isArrayType())
705      return EmitArrayInitialization(ILE);
706
707    if (ILE->getType()->isRecordType())
708      return EmitStructInitialization(ILE);
709
710    if (ILE->getType()->isUnionType())
711      return EmitUnionInitialization(ILE);
712
713    // If ILE was a constant vector, we would have handled it already.
714    if (ILE->getType()->isVectorType())
715      return 0;
716
717    assert(0 && "Unable to handle InitListExpr");
718    // Get rid of control reaches end of void function warning.
719    // Not reached.
720    return 0;
721  }
722
723  llvm::Constant *VisitCXXConstructExpr(CXXConstructExpr *E) {
724    if (!E->getConstructor()->isTrivial())
725      return 0;
726
727    QualType Ty = E->getType();
728
729    // FIXME: We should not have to call getBaseElementType here.
730    const RecordType *RT =
731      CGM.getContext().getBaseElementType(Ty)->getAs<RecordType>();
732    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
733
734    // If the class doesn't have a trivial destructor, we can't emit it as a
735    // constant expr.
736    if (!RD->hasTrivialDestructor())
737      return 0;
738
739    // Only copy and default constructors can be trivial.
740
741
742    if (E->getNumArgs()) {
743      assert(E->getNumArgs() == 1 && "trivial ctor with > 1 argument");
744      assert(E->getConstructor()->isCopyConstructor() &&
745             "trivial ctor has argument but isn't a copy ctor");
746
747      Expr *Arg = E->getArg(0);
748      assert(CGM.getContext().hasSameUnqualifiedType(Ty, Arg->getType()) &&
749             "argument to copy ctor is of wrong type");
750
751      return Visit(Arg);
752    }
753
754    return CGM.EmitNullConstant(Ty);
755  }
756
757  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
758    assert(!E->getType()->isPointerType() && "Strings are always arrays");
759
760    // This must be a string initializing an array in a static initializer.
761    // Don't emit it as the address of the string, emit the string data itself
762    // as an inline array.
763    return llvm::ConstantArray::get(VMContext,
764                                    CGM.GetStringForStringLiteral(E), false);
765  }
766
767  llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
768    // This must be an @encode initializing an array in a static initializer.
769    // Don't emit it as the address of the string, emit the string data itself
770    // as an inline array.
771    std::string Str;
772    CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
773    const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
774
775    // Resize the string to the right size, adding zeros at the end, or
776    // truncating as needed.
777    Str.resize(CAT->getSize().getZExtValue(), '\0');
778    return llvm::ConstantArray::get(VMContext, Str, false);
779  }
780
781  llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
782    return Visit(E->getSubExpr());
783  }
784
785  // Utility methods
786  const llvm::Type *ConvertType(QualType T) {
787    return CGM.getTypes().ConvertType(T);
788  }
789
790public:
791  llvm::Constant *EmitLValue(Expr *E) {
792    switch (E->getStmtClass()) {
793    default: break;
794    case Expr::CompoundLiteralExprClass: {
795      // Note that due to the nature of compound literals, this is guaranteed
796      // to be the only use of the variable, so we just generate it here.
797      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
798      llvm::Constant* C = Visit(CLE->getInitializer());
799      // FIXME: "Leaked" on failure.
800      if (C)
801        C = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
802                                     E->getType().isConstant(CGM.getContext()),
803                                     llvm::GlobalValue::InternalLinkage,
804                                     C, ".compoundliteral", 0, false,
805                          CGM.getContext().getTargetAddressSpace(E->getType()));
806      return C;
807    }
808    case Expr::DeclRefExprClass: {
809      ValueDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
810      if (Decl->hasAttr<WeakRefAttr>())
811        return CGM.GetWeakRefReference(Decl);
812      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
813        return CGM.GetAddrOfFunction(FD);
814      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
815        // We can never refer to a variable with local storage.
816        if (!VD->hasLocalStorage()) {
817          if (VD->isFileVarDecl() || VD->hasExternalStorage())
818            return CGM.GetAddrOfGlobalVar(VD);
819          else if (VD->isLocalVarDecl()) {
820            assert(CGF && "Can't access static local vars without CGF");
821            return CGF->GetAddrOfStaticLocalVar(VD);
822          }
823        }
824      }
825      break;
826    }
827    case Expr::StringLiteralClass:
828      return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
829    case Expr::ObjCEncodeExprClass:
830      return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
831    case Expr::ObjCStringLiteralClass: {
832      ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
833      llvm::Constant *C =
834          CGM.getObjCRuntime().GenerateConstantString(SL->getString());
835      return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
836    }
837    case Expr::PredefinedExprClass: {
838      unsigned Type = cast<PredefinedExpr>(E)->getIdentType();
839      if (CGF) {
840        LValue Res = CGF->EmitPredefinedLValue(cast<PredefinedExpr>(E));
841        return cast<llvm::Constant>(Res.getAddress());
842      } else if (Type == PredefinedExpr::PrettyFunction) {
843        return CGM.GetAddrOfConstantCString("top level", ".tmp");
844      }
845
846      return CGM.GetAddrOfConstantCString("", ".tmp");
847    }
848    case Expr::AddrLabelExprClass: {
849      assert(CGF && "Invalid address of label expression outside function.");
850      llvm::Constant *Ptr =
851        CGF->GetAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
852      return llvm::ConstantExpr::getBitCast(Ptr, ConvertType(E->getType()));
853    }
854    case Expr::CallExprClass: {
855      CallExpr* CE = cast<CallExpr>(E);
856      unsigned builtin = CE->isBuiltinCall(CGM.getContext());
857      if (builtin !=
858            Builtin::BI__builtin___CFStringMakeConstantString &&
859          builtin !=
860            Builtin::BI__builtin___NSStringMakeConstantString)
861        break;
862      const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
863      const StringLiteral *Literal = cast<StringLiteral>(Arg);
864      if (builtin ==
865            Builtin::BI__builtin___NSStringMakeConstantString) {
866        return CGM.getObjCRuntime().GenerateConstantString(Literal);
867      }
868      // FIXME: need to deal with UCN conversion issues.
869      return CGM.GetAddrOfConstantCFString(Literal);
870    }
871    case Expr::BlockExprClass: {
872      std::string FunctionName;
873      if (CGF)
874        FunctionName = CGF->CurFn->getName();
875      else
876        FunctionName = "global";
877
878      return CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
879    }
880    }
881
882    return 0;
883  }
884};
885
886}  // end anonymous namespace.
887
888llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
889                                                QualType DestType,
890                                                CodeGenFunction *CGF) {
891  Expr::EvalResult Result;
892
893  bool Success = false;
894
895  if (DestType->isReferenceType())
896    Success = E->EvaluateAsLValue(Result, Context);
897  else
898    Success = E->Evaluate(Result, Context);
899
900  if (Success && !Result.HasSideEffects) {
901    switch (Result.Val.getKind()) {
902    case APValue::Uninitialized:
903      assert(0 && "Constant expressions should be initialized.");
904      return 0;
905    case APValue::LValue: {
906      const llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
907      llvm::Constant *Offset =
908        llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext),
909                               Result.Val.getLValueOffset().getQuantity());
910
911      llvm::Constant *C;
912      if (const Expr *LVBase = Result.Val.getLValueBase()) {
913        C = ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
914
915        // Apply offset if necessary.
916        if (!Offset->isNullValue()) {
917          const llvm::Type *Type = llvm::Type::getInt8PtrTy(VMContext);
918          llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
919          Casted = llvm::ConstantExpr::getGetElementPtr(Casted, &Offset, 1);
920          C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
921        }
922
923        // Convert to the appropriate type; this could be an lvalue for
924        // an integer.
925        if (isa<llvm::PointerType>(DestTy))
926          return llvm::ConstantExpr::getBitCast(C, DestTy);
927
928        return llvm::ConstantExpr::getPtrToInt(C, DestTy);
929      } else {
930        C = Offset;
931
932        // Convert to the appropriate type; this could be an lvalue for
933        // an integer.
934        if (isa<llvm::PointerType>(DestTy))
935          return llvm::ConstantExpr::getIntToPtr(C, DestTy);
936
937        // If the types don't match this should only be a truncate.
938        if (C->getType() != DestTy)
939          return llvm::ConstantExpr::getTrunc(C, DestTy);
940
941        return C;
942      }
943    }
944    case APValue::Int: {
945      llvm::Constant *C = llvm::ConstantInt::get(VMContext,
946                                                 Result.Val.getInt());
947
948      if (C->getType()->isIntegerTy(1)) {
949        const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
950        C = llvm::ConstantExpr::getZExt(C, BoolTy);
951      }
952      return C;
953    }
954    case APValue::ComplexInt: {
955      llvm::Constant *Complex[2];
956
957      Complex[0] = llvm::ConstantInt::get(VMContext,
958                                          Result.Val.getComplexIntReal());
959      Complex[1] = llvm::ConstantInt::get(VMContext,
960                                          Result.Val.getComplexIntImag());
961
962      // FIXME: the target may want to specify that this is packed.
963      return llvm::ConstantStruct::get(VMContext, Complex, 2, false);
964    }
965    case APValue::Float:
966      return llvm::ConstantFP::get(VMContext, Result.Val.getFloat());
967    case APValue::ComplexFloat: {
968      llvm::Constant *Complex[2];
969
970      Complex[0] = llvm::ConstantFP::get(VMContext,
971                                         Result.Val.getComplexFloatReal());
972      Complex[1] = llvm::ConstantFP::get(VMContext,
973                                         Result.Val.getComplexFloatImag());
974
975      // FIXME: the target may want to specify that this is packed.
976      return llvm::ConstantStruct::get(VMContext, Complex, 2, false);
977    }
978    case APValue::Vector: {
979      llvm::SmallVector<llvm::Constant *, 4> Inits;
980      unsigned NumElts = Result.Val.getVectorLength();
981
982      for (unsigned i = 0; i != NumElts; ++i) {
983        APValue &Elt = Result.Val.getVectorElt(i);
984        if (Elt.isInt())
985          Inits.push_back(llvm::ConstantInt::get(VMContext, Elt.getInt()));
986        else
987          Inits.push_back(llvm::ConstantFP::get(VMContext, Elt.getFloat()));
988      }
989      return llvm::ConstantVector::get(Inits);
990    }
991    }
992  }
993
994  llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
995  if (C && C->getType()->isIntegerTy(1)) {
996    const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
997    C = llvm::ConstantExpr::getZExt(C, BoolTy);
998  }
999  return C;
1000}
1001
1002static uint64_t getFieldOffset(ASTContext &C, const FieldDecl *field) {
1003  const ASTRecordLayout &layout = C.getASTRecordLayout(field->getParent());
1004  return layout.getFieldOffset(field->getFieldIndex());
1005}
1006
1007llvm::Constant *
1008CodeGenModule::getMemberPointerConstant(const UnaryOperator *uo) {
1009  // Member pointer constants always have a very particular form.
1010  const MemberPointerType *type = cast<MemberPointerType>(uo->getType());
1011  const ValueDecl *decl = cast<DeclRefExpr>(uo->getSubExpr())->getDecl();
1012
1013  // A member function pointer.
1014  if (const CXXMethodDecl *method = dyn_cast<CXXMethodDecl>(decl))
1015    return getCXXABI().EmitMemberPointer(method);
1016
1017  // Otherwise, a member data pointer.
1018  uint64_t fieldOffset;
1019  if (const FieldDecl *field = dyn_cast<FieldDecl>(decl))
1020    fieldOffset = getFieldOffset(getContext(), field);
1021  else {
1022    const IndirectFieldDecl *ifield = cast<IndirectFieldDecl>(decl);
1023
1024    fieldOffset = 0;
1025    for (IndirectFieldDecl::chain_iterator ci = ifield->chain_begin(),
1026           ce = ifield->chain_end(); ci != ce; ++ci)
1027      fieldOffset += getFieldOffset(getContext(), cast<FieldDecl>(*ci));
1028  }
1029
1030  CharUnits chars = getContext().toCharUnitsFromBits((int64_t) fieldOffset);
1031  return getCXXABI().EmitMemberDataPointer(type, chars);
1032}
1033
1034static void
1035FillInNullDataMemberPointers(CodeGenModule &CGM, QualType T,
1036                             std::vector<llvm::Constant *> &Elements,
1037                             uint64_t StartOffset) {
1038  assert(StartOffset % 8 == 0 && "StartOffset not byte aligned!");
1039
1040  if (CGM.getTypes().isZeroInitializable(T))
1041    return;
1042
1043  if (const ConstantArrayType *CAT =
1044        CGM.getContext().getAsConstantArrayType(T)) {
1045    QualType ElementTy = CAT->getElementType();
1046    uint64_t ElementSize = CGM.getContext().getTypeSize(ElementTy);
1047
1048    for (uint64_t I = 0, E = CAT->getSize().getZExtValue(); I != E; ++I) {
1049      FillInNullDataMemberPointers(CGM, ElementTy, Elements,
1050                                   StartOffset + I * ElementSize);
1051    }
1052  } else if (const RecordType *RT = T->getAs<RecordType>()) {
1053    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
1054    const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
1055
1056    // Go through all bases and fill in any null pointer to data members.
1057    for (CXXRecordDecl::base_class_const_iterator I = RD->bases_begin(),
1058         E = RD->bases_end(); I != E; ++I) {
1059      if (I->isVirtual()) {
1060        // Ignore virtual bases.
1061        continue;
1062      }
1063
1064      const CXXRecordDecl *BaseDecl =
1065      cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());
1066
1067      // Ignore empty bases.
1068      if (BaseDecl->isEmpty())
1069        continue;
1070
1071      // Ignore bases that don't have any pointer to data members.
1072      if (CGM.getTypes().isZeroInitializable(BaseDecl))
1073        continue;
1074
1075      uint64_t BaseOffset = Layout.getBaseClassOffsetInBits(BaseDecl);
1076      FillInNullDataMemberPointers(CGM, I->getType(),
1077                                   Elements, StartOffset + BaseOffset);
1078    }
1079
1080    // Visit all fields.
1081    unsigned FieldNo = 0;
1082    for (RecordDecl::field_iterator I = RD->field_begin(),
1083         E = RD->field_end(); I != E; ++I, ++FieldNo) {
1084      QualType FieldType = I->getType();
1085
1086      if (CGM.getTypes().isZeroInitializable(FieldType))
1087        continue;
1088
1089      uint64_t FieldOffset = StartOffset + Layout.getFieldOffset(FieldNo);
1090      FillInNullDataMemberPointers(CGM, FieldType, Elements, FieldOffset);
1091    }
1092  } else {
1093    assert(T->isMemberPointerType() && "Should only see member pointers here!");
1094    assert(!T->getAs<MemberPointerType>()->getPointeeType()->isFunctionType() &&
1095           "Should only see pointers to data members here!");
1096
1097    uint64_t StartIndex = StartOffset / 8;
1098    uint64_t EndIndex = StartIndex + CGM.getContext().getTypeSize(T) / 8;
1099
1100    // FIXME: hardcodes Itanium member pointer representation!
1101    llvm::Constant *NegativeOne =
1102      llvm::ConstantInt::get(llvm::Type::getInt8Ty(CGM.getLLVMContext()),
1103                             -1ULL, /*isSigned*/true);
1104
1105    // Fill in the null data member pointer.
1106    for (uint64_t I = StartIndex; I != EndIndex; ++I)
1107      Elements[I] = NegativeOne;
1108  }
1109}
1110
1111static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
1112                                               const llvm::Type *baseType,
1113                                               const CXXRecordDecl *base);
1114
1115static llvm::Constant *EmitNullConstant(CodeGenModule &CGM,
1116                                        const CXXRecordDecl *record,
1117                                        bool asCompleteObject) {
1118  const CGRecordLayout &layout = CGM.getTypes().getCGRecordLayout(record);
1119  const llvm::StructType *structure =
1120    (asCompleteObject ? layout.getLLVMType()
1121                      : layout.getBaseSubobjectLLVMType());
1122
1123  unsigned numElements = structure->getNumElements();
1124  std::vector<llvm::Constant *> elements(numElements);
1125
1126  // Fill in all the bases.
1127  for (CXXRecordDecl::base_class_const_iterator
1128         I = record->bases_begin(), E = record->bases_end(); I != E; ++I) {
1129    if (I->isVirtual()) {
1130      // Ignore virtual bases; if we're laying out for a complete
1131      // object, we'll lay these out later.
1132      continue;
1133    }
1134
1135    const CXXRecordDecl *base =
1136      cast<CXXRecordDecl>(I->getType()->castAs<RecordType>()->getDecl());
1137
1138    // Ignore empty bases.
1139    if (base->isEmpty())
1140      continue;
1141
1142    unsigned fieldIndex = layout.getNonVirtualBaseLLVMFieldNo(base);
1143    const llvm::Type *baseType = structure->getElementType(fieldIndex);
1144    elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
1145  }
1146
1147  // Fill in all the fields.
1148  for (RecordDecl::field_iterator I = record->field_begin(),
1149         E = record->field_end(); I != E; ++I) {
1150    const FieldDecl *field = *I;
1151
1152    // Ignore bit fields.
1153    if (field->isBitField())
1154      continue;
1155
1156    unsigned fieldIndex = layout.getLLVMFieldNo(field);
1157    elements[fieldIndex] = CGM.EmitNullConstant(field->getType());
1158  }
1159
1160  // Fill in the virtual bases, if we're working with the complete object.
1161  if (asCompleteObject) {
1162    for (CXXRecordDecl::base_class_const_iterator
1163           I = record->vbases_begin(), E = record->vbases_end(); I != E; ++I) {
1164      const CXXRecordDecl *base =
1165        cast<CXXRecordDecl>(I->getType()->castAs<RecordType>()->getDecl());
1166
1167      // Ignore empty bases.
1168      if (base->isEmpty())
1169        continue;
1170
1171      unsigned fieldIndex = layout.getVirtualBaseIndex(base);
1172
1173      // We might have already laid this field out.
1174      if (elements[fieldIndex]) continue;
1175
1176      const llvm::Type *baseType = structure->getElementType(fieldIndex);
1177      elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
1178    }
1179  }
1180
1181  // Now go through all other fields and zero them out.
1182  for (unsigned i = 0; i != numElements; ++i) {
1183    if (!elements[i])
1184      elements[i] = llvm::Constant::getNullValue(structure->getElementType(i));
1185  }
1186
1187  return llvm::ConstantStruct::get(structure, elements);
1188}
1189
1190/// Emit the null constant for a base subobject.
1191static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
1192                                               const llvm::Type *baseType,
1193                                               const CXXRecordDecl *base) {
1194  const CGRecordLayout &baseLayout = CGM.getTypes().getCGRecordLayout(base);
1195
1196  // Just zero out bases that don't have any pointer to data members.
1197  if (baseLayout.isZeroInitializableAsBase())
1198    return llvm::Constant::getNullValue(baseType);
1199
1200  // If the base type is a struct, we can just use its null constant.
1201  if (isa<llvm::StructType>(baseType)) {
1202    return EmitNullConstant(CGM, base, /*complete*/ false);
1203  }
1204
1205  // Otherwise, some bases are represented as arrays of i8 if the size
1206  // of the base is smaller than its corresponding LLVM type.  Figure
1207  // out how many elements this base array has.
1208  const llvm::ArrayType *baseArrayType = cast<llvm::ArrayType>(baseType);
1209  unsigned numBaseElements = baseArrayType->getNumElements();
1210
1211  // Fill in null data member pointers.
1212  std::vector<llvm::Constant *> baseElements(numBaseElements);
1213  FillInNullDataMemberPointers(CGM, CGM.getContext().getTypeDeclType(base),
1214                               baseElements, 0);
1215
1216  // Now go through all other elements and zero them out.
1217  if (numBaseElements) {
1218    const llvm::Type *i8 = llvm::Type::getInt8Ty(CGM.getLLVMContext());
1219    llvm::Constant *i8_zero = llvm::Constant::getNullValue(i8);
1220    for (unsigned i = 0; i != numBaseElements; ++i) {
1221      if (!baseElements[i])
1222        baseElements[i] = i8_zero;
1223    }
1224  }
1225
1226  return llvm::ConstantArray::get(baseArrayType, baseElements);
1227}
1228
1229llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
1230  if (getTypes().isZeroInitializable(T))
1231    return llvm::Constant::getNullValue(getTypes().ConvertTypeForMem(T));
1232
1233  if (const ConstantArrayType *CAT = Context.getAsConstantArrayType(T)) {
1234
1235    QualType ElementTy = CAT->getElementType();
1236
1237    llvm::Constant *Element = EmitNullConstant(ElementTy);
1238    unsigned NumElements = CAT->getSize().getZExtValue();
1239    std::vector<llvm::Constant *> Array(NumElements);
1240    for (unsigned i = 0; i != NumElements; ++i)
1241      Array[i] = Element;
1242
1243    const llvm::ArrayType *ATy =
1244      cast<llvm::ArrayType>(getTypes().ConvertTypeForMem(T));
1245    return llvm::ConstantArray::get(ATy, Array);
1246  }
1247
1248  if (const RecordType *RT = T->getAs<RecordType>()) {
1249    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
1250    return ::EmitNullConstant(*this, RD, /*complete object*/ true);
1251  }
1252
1253  assert(T->isMemberPointerType() && "Should only see member pointers here!");
1254  assert(!T->getAs<MemberPointerType>()->getPointeeType()->isFunctionType() &&
1255         "Should only see pointers to data members here!");
1256
1257  // Itanium C++ ABI 2.3:
1258  //   A NULL pointer is represented as -1.
1259  return getCXXABI().EmitNullMemberPointer(T->castAs<MemberPointerType>());
1260}
1261