CGExprConstant.cpp revision 35f18a5e8b5a434894a4886ed98f3dbaa3b895c0 
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  SmallVector<llvm::Constant *, 16> Elements;
44public:
45  static llvm::Constant *BuildStruct(CodeGenModule &CGM, CodeGenFunction *CGF,
46                                     InitListExpr *ILE);
47  static llvm::Constant *BuildStruct(CodeGenModule &CGM, CodeGenFunction *CGF,
48                                     const APValue &Value, QualType ValTy);
49
50private:
51  ConstStructBuilder(CodeGenModule &CGM, CodeGenFunction *CGF)
52    : CGM(CGM), CGF(CGF), Packed(false),
53    NextFieldOffsetInChars(CharUnits::Zero()),
54    LLVMStructAlignment(CharUnits::One()) { }
55
56  void AppendField(const FieldDecl *Field, uint64_t FieldOffset,
57                   llvm::Constant *InitExpr);
58
59  void AppendBitField(const FieldDecl *Field, uint64_t FieldOffset,
60                      llvm::ConstantInt *InitExpr);
61
62  void AppendPadding(CharUnits PadSize);
63
64  void AppendTailPadding(CharUnits RecordSize);
65
66  void ConvertStructToPacked();
67
68  bool Build(InitListExpr *ILE);
69  void Build(const APValue &Val, QualType ValTy);
70  llvm::Constant *Finalize(QualType Ty);
71
72  CharUnits getAlignment(const llvm::Constant *C) const {
73    if (Packed)  return CharUnits::One();
74    return CharUnits::fromQuantity(
75        CGM.getTargetData().getABITypeAlignment(C->getType()));
76  }
77
78  CharUnits getSizeInChars(const llvm::Constant *C) const {
79    return CharUnits::fromQuantity(
80        CGM.getTargetData().getTypeAllocSize(C->getType()));
81  }
82};
83
84void ConstStructBuilder::
85AppendField(const FieldDecl *Field, uint64_t FieldOffset,
86            llvm::Constant *InitCst) {
87
88  const ASTContext &Context = CGM.getContext();
89
90  CharUnits FieldOffsetInChars = Context.toCharUnitsFromBits(FieldOffset);
91
92  assert(NextFieldOffsetInChars <= FieldOffsetInChars
93         && "Field offset mismatch!");
94
95  CharUnits FieldAlignment = getAlignment(InitCst);
96
97  // Round up the field offset to the alignment of the field type.
98  CharUnits AlignedNextFieldOffsetInChars =
99    NextFieldOffsetInChars.RoundUpToAlignment(FieldAlignment);
100
101  if (AlignedNextFieldOffsetInChars > FieldOffsetInChars) {
102    assert(!Packed && "Alignment is wrong even with a packed struct!");
103
104    // Convert the struct to a packed struct.
105    ConvertStructToPacked();
106
107    AlignedNextFieldOffsetInChars = NextFieldOffsetInChars;
108  }
109
110  if (AlignedNextFieldOffsetInChars < FieldOffsetInChars) {
111    // We need to append padding.
112    AppendPadding(FieldOffsetInChars - NextFieldOffsetInChars);
113
114    assert(NextFieldOffsetInChars == FieldOffsetInChars &&
115           "Did not add enough padding!");
116
117    AlignedNextFieldOffsetInChars = NextFieldOffsetInChars;
118  }
119
120  // Add the field.
121  Elements.push_back(InitCst);
122  NextFieldOffsetInChars = AlignedNextFieldOffsetInChars +
123                           getSizeInChars(InitCst);
124
125  if (Packed)
126    assert(LLVMStructAlignment == CharUnits::One() &&
127           "Packed struct not byte-aligned!");
128  else
129    LLVMStructAlignment = std::max(LLVMStructAlignment, FieldAlignment);
130}
131
132void ConstStructBuilder::AppendBitField(const FieldDecl *Field,
133                                        uint64_t FieldOffset,
134                                        llvm::ConstantInt *CI) {
135  const ASTContext &Context = CGM.getContext();
136  const uint64_t CharWidth = Context.getCharWidth();
137  uint64_t NextFieldOffsetInBits = Context.toBits(NextFieldOffsetInChars);
138  if (FieldOffset > NextFieldOffsetInBits) {
139    // We need to add padding.
140    CharUnits PadSize = Context.toCharUnitsFromBits(
141      llvm::RoundUpToAlignment(FieldOffset - NextFieldOffsetInBits,
142                               Context.getTargetInfo().getCharAlign()));
143
144    AppendPadding(PadSize);
145  }
146
147  uint64_t FieldSize = Field->getBitWidthValue(Context);
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  SmallVector<llvm::Constant *, 16> 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.swap(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      AppendField(*Field, Layout.getFieldOffset(FieldNo), EltInit);
387    } else {
388      // Otherwise we have a bitfield.
389      AppendBitField(*Field, Layout.getFieldOffset(FieldNo),
390                     cast<llvm::ConstantInt>(EltInit));
391    }
392  }
393
394  return true;
395}
396
397void ConstStructBuilder::Build(const APValue &Val, QualType ValTy) {
398  RecordDecl *RD = ValTy->getAs<RecordType>()->getDecl();
399  const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
400
401  if (CXXRecordDecl *CD = dyn_cast<CXXRecordDecl>(RD)) {
402    unsigned BaseNo = 0;
403    for (CXXRecordDecl::base_class_iterator Base = CD->bases_begin(),
404         BaseEnd = CD->bases_end(); Base != BaseEnd; ++Base, ++BaseNo) {
405      // Build the base class subobject at the appropriately-offset location
406      // within this object.
407      const CXXRecordDecl *BD = Base->getType()->getAsCXXRecordDecl();
408      CharUnits BaseOffset = Layout.getBaseClassOffset(BD);
409      NextFieldOffsetInChars -= BaseOffset;
410
411      Build(Val.getStructBase(BaseNo), Base->getType());
412
413      NextFieldOffsetInChars += BaseOffset;
414    }
415  }
416
417  unsigned FieldNo = 0;
418  const FieldDecl *LastFD = 0;
419  bool IsMsStruct = RD->hasAttr<MsStructAttr>();
420
421  for (RecordDecl::field_iterator Field = RD->field_begin(),
422       FieldEnd = RD->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
423    if (IsMsStruct) {
424      // Zero-length bitfields following non-bitfield members are
425      // ignored:
426      if (CGM.getContext().ZeroBitfieldFollowsNonBitfield((*Field), LastFD)) {
427        --FieldNo;
428        continue;
429      }
430      LastFD = (*Field);
431    }
432
433    // If this is a union, skip all the fields that aren't being initialized.
434    if (RD->isUnion() && Val.getUnionField() != *Field)
435      continue;
436
437    // Don't emit anonymous bitfields, they just affect layout.
438    if (Field->isUnnamedBitfield()) {
439      LastFD = (*Field);
440      continue;
441    }
442
443    // Emit the value of the initializer.
444    const APValue &FieldValue =
445      RD->isUnion() ? Val.getUnionValue() : Val.getStructField(FieldNo);
446    llvm::Constant *EltInit =
447      CGM.EmitConstantValue(FieldValue, Field->getType(), CGF);
448    assert(EltInit && "EmitConstantValue can't fail");
449
450    if (!Field->isBitField()) {
451      // Handle non-bitfield members.
452      AppendField(*Field, Layout.getFieldOffset(FieldNo), EltInit);
453    } else {
454      // Otherwise we have a bitfield.
455      AppendBitField(*Field, Layout.getFieldOffset(FieldNo),
456                     cast<llvm::ConstantInt>(EltInit));
457    }
458  }
459}
460
461llvm::Constant *ConstStructBuilder::Finalize(QualType Ty) {
462  RecordDecl *RD = Ty->getAs<RecordType>()->getDecl();
463  const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
464
465  CharUnits LayoutSizeInChars = Layout.getSize();
466
467  if (NextFieldOffsetInChars > LayoutSizeInChars) {
468    // If the struct is bigger than the size of the record type,
469    // we must have a flexible array member at the end.
470    assert(RD->hasFlexibleArrayMember() &&
471           "Must have flexible array member if struct is bigger than type!");
472
473    // No tail padding is necessary.
474  } else {
475    // Append tail padding if necessary.
476    AppendTailPadding(LayoutSizeInChars);
477
478    CharUnits LLVMSizeInChars =
479      NextFieldOffsetInChars.RoundUpToAlignment(LLVMStructAlignment);
480
481    // Check if we need to convert the struct to a packed struct.
482    if (NextFieldOffsetInChars <= LayoutSizeInChars &&
483        LLVMSizeInChars > LayoutSizeInChars) {
484      assert(!Packed && "Size mismatch!");
485
486      ConvertStructToPacked();
487      assert(NextFieldOffsetInChars <= LayoutSizeInChars &&
488             "Converting to packed did not help!");
489    }
490
491    assert(LayoutSizeInChars == NextFieldOffsetInChars &&
492           "Tail padding mismatch!");
493  }
494
495  // Pick the type to use.  If the type is layout identical to the ConvertType
496  // type then use it, otherwise use whatever the builder produced for us.
497  llvm::StructType *STy =
498      llvm::ConstantStruct::getTypeForElements(CGM.getLLVMContext(),
499                                               Elements, Packed);
500  llvm::Type *ValTy = CGM.getTypes().ConvertType(Ty);
501  if (llvm::StructType *ValSTy = dyn_cast<llvm::StructType>(ValTy)) {
502    if (ValSTy->isLayoutIdentical(STy))
503      STy = ValSTy;
504  }
505
506  llvm::Constant *Result = llvm::ConstantStruct::get(STy, Elements);
507
508  assert(NextFieldOffsetInChars.RoundUpToAlignment(getAlignment(Result)) ==
509         getSizeInChars(Result) && "Size mismatch!");
510
511  return Result;
512}
513
514llvm::Constant *ConstStructBuilder::BuildStruct(CodeGenModule &CGM,
515                                                CodeGenFunction *CGF,
516                                                InitListExpr *ILE) {
517  ConstStructBuilder Builder(CGM, CGF);
518
519  if (!Builder.Build(ILE))
520    return 0;
521
522  return Builder.Finalize(ILE->getType());
523}
524
525llvm::Constant *ConstStructBuilder::BuildStruct(CodeGenModule &CGM,
526                                                CodeGenFunction *CGF,
527                                                const APValue &Val,
528                                                QualType ValTy) {
529  ConstStructBuilder Builder(CGM, CGF);
530  Builder.Build(Val, ValTy);
531  return Builder.Finalize(ValTy);
532}
533
534
535//===----------------------------------------------------------------------===//
536//                             ConstExprEmitter
537//===----------------------------------------------------------------------===//
538
539/// This class only needs to handle two cases:
540/// 1) Literals (this is used by APValue emission to emit literals).
541/// 2) Arrays, structs and unions (outside C++11 mode, we don't currently
542///    constant fold these types).
543class ConstExprEmitter :
544  public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
545  CodeGenModule &CGM;
546  CodeGenFunction *CGF;
547  llvm::LLVMContext &VMContext;
548public:
549  ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
550    : CGM(cgm), CGF(cgf), VMContext(cgm.getLLVMContext()) {
551  }
552
553  //===--------------------------------------------------------------------===//
554  //                            Visitor Methods
555  //===--------------------------------------------------------------------===//
556
557  llvm::Constant *VisitStmt(Stmt *S) {
558    return 0;
559  }
560
561  llvm::Constant *VisitParenExpr(ParenExpr *PE) {
562    return Visit(PE->getSubExpr());
563  }
564
565  llvm::Constant *
566  VisitSubstNonTypeTemplateParmExpr(SubstNonTypeTemplateParmExpr *PE) {
567    return Visit(PE->getReplacement());
568  }
569
570  llvm::Constant *VisitGenericSelectionExpr(GenericSelectionExpr *GE) {
571    return Visit(GE->getResultExpr());
572  }
573
574  llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
575    return Visit(E->getInitializer());
576  }
577
578  llvm::Constant *VisitCastExpr(CastExpr* E) {
579    Expr *subExpr = E->getSubExpr();
580    llvm::Constant *C = CGM.EmitConstantExpr(subExpr, subExpr->getType(), CGF);
581    if (!C) return 0;
582
583    llvm::Type *destType = ConvertType(E->getType());
584
585    switch (E->getCastKind()) {
586    case CK_ToUnion: {
587      // GCC cast to union extension
588      assert(E->getType()->isUnionType() &&
589             "Destination type is not union type!");
590
591      // Build a struct with the union sub-element as the first member,
592      // and padded to the appropriate size
593      std::vector<llvm::Constant*> Elts;
594      std::vector<llvm::Type*> Types;
595      Elts.push_back(C);
596      Types.push_back(C->getType());
597      unsigned CurSize = CGM.getTargetData().getTypeAllocSize(C->getType());
598      unsigned TotalSize = CGM.getTargetData().getTypeAllocSize(destType);
599
600      assert(CurSize <= TotalSize && "Union size mismatch!");
601      if (unsigned NumPadBytes = TotalSize - CurSize) {
602        llvm::Type *Ty = llvm::Type::getInt8Ty(VMContext);
603        if (NumPadBytes > 1)
604          Ty = llvm::ArrayType::get(Ty, NumPadBytes);
605
606        Elts.push_back(llvm::UndefValue::get(Ty));
607        Types.push_back(Ty);
608      }
609
610      llvm::StructType* STy =
611        llvm::StructType::get(C->getType()->getContext(), Types, false);
612      return llvm::ConstantStruct::get(STy, Elts);
613    }
614
615    case CK_LValueToRValue:
616    case CK_AtomicToNonAtomic:
617    case CK_NonAtomicToAtomic:
618    case CK_NoOp:
619      return C;
620
621    case CK_Dependent: llvm_unreachable("saw dependent cast!");
622
623    // These will never be supported.
624    case CK_ObjCObjectLValueCast:
625    case CK_ARCProduceObject:
626    case CK_ARCConsumeObject:
627    case CK_ARCReclaimReturnedObject:
628    case CK_ARCExtendBlockObject:
629      return 0;
630
631    // These don't need to be handled here because Evaluate knows how to
632    // evaluate them in the cases where they can be folded.
633    case CK_ToVoid:
634    case CK_Dynamic:
635    case CK_LValueBitCast:
636    case CK_NullToMemberPointer:
637    case CK_DerivedToBaseMemberPointer:
638    case CK_BaseToDerivedMemberPointer:
639    case CK_UserDefinedConversion:
640    case CK_ConstructorConversion:
641    case CK_CPointerToObjCPointerCast:
642    case CK_BlockPointerToObjCPointerCast:
643    case CK_AnyPointerToBlockPointerCast:
644    case CK_BitCast:
645    case CK_ArrayToPointerDecay:
646    case CK_FunctionToPointerDecay:
647    case CK_BaseToDerived:
648    case CK_DerivedToBase:
649    case CK_UncheckedDerivedToBase:
650    case CK_MemberPointerToBoolean:
651    case CK_VectorSplat:
652    case CK_FloatingRealToComplex:
653    case CK_FloatingComplexToReal:
654    case CK_FloatingComplexToBoolean:
655    case CK_FloatingComplexCast:
656    case CK_FloatingComplexToIntegralComplex:
657    case CK_IntegralRealToComplex:
658    case CK_IntegralComplexToReal:
659    case CK_IntegralComplexToBoolean:
660    case CK_IntegralComplexCast:
661    case CK_IntegralComplexToFloatingComplex:
662    case CK_PointerToIntegral:
663    case CK_PointerToBoolean:
664    case CK_NullToPointer:
665    case CK_IntegralCast:
666    case CK_IntegralToPointer:
667    case CK_IntegralToBoolean:
668    case CK_IntegralToFloating:
669    case CK_FloatingToIntegral:
670    case CK_FloatingToBoolean:
671    case CK_FloatingCast:
672      return 0;
673    }
674    llvm_unreachable("Invalid CastKind");
675  }
676
677  llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
678    return Visit(DAE->getExpr());
679  }
680
681  llvm::Constant *VisitMaterializeTemporaryExpr(MaterializeTemporaryExpr *E) {
682    return Visit(E->GetTemporaryExpr());
683  }
684
685  llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
686    unsigned NumInitElements = ILE->getNumInits();
687    if (NumInitElements == 1 && ILE->getType() == ILE->getInit(0)->getType() &&
688        (isa<StringLiteral>(ILE->getInit(0)) ||
689         isa<ObjCEncodeExpr>(ILE->getInit(0))))
690      return Visit(ILE->getInit(0));
691
692    std::vector<llvm::Constant*> Elts;
693    llvm::ArrayType *AType =
694        cast<llvm::ArrayType>(ConvertType(ILE->getType()));
695    llvm::Type *ElemTy = AType->getElementType();
696    unsigned NumElements = AType->getNumElements();
697
698    // Initialising an array requires us to automatically
699    // initialise any elements that have not been initialised explicitly
700    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
701
702    // Copy initializer elements.
703    unsigned i = 0;
704    bool RewriteType = false;
705    for (; i < NumInitableElts; ++i) {
706      Expr *Init = ILE->getInit(i);
707      llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
708      if (!C)
709        return 0;
710      RewriteType |= (C->getType() != ElemTy);
711      Elts.push_back(C);
712    }
713
714    // Initialize remaining array elements.
715    // FIXME: This doesn't handle member pointers correctly!
716    llvm::Constant *fillC;
717    if (Expr *filler = ILE->getArrayFiller())
718      fillC = CGM.EmitConstantExpr(filler, filler->getType(), CGF);
719    else
720      fillC = llvm::Constant::getNullValue(ElemTy);
721    if (!fillC)
722      return 0;
723    RewriteType |= (fillC->getType() != ElemTy);
724    for (; i < NumElements; ++i)
725      Elts.push_back(fillC);
726
727    if (RewriteType) {
728      // FIXME: Try to avoid packing the array
729      std::vector<llvm::Type*> Types;
730      for (unsigned i = 0, e = Elts.size(); i < e; ++i)
731        Types.push_back(Elts[i]->getType());
732      llvm::StructType *SType = llvm::StructType::get(AType->getContext(),
733                                                            Types, true);
734      return llvm::ConstantStruct::get(SType, Elts);
735    }
736
737    return llvm::ConstantArray::get(AType, Elts);
738  }
739
740  llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
741    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
742  }
743
744  llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
745    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
746  }
747
748  llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
749    return CGM.EmitNullConstant(E->getType());
750  }
751
752  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
753    if (ILE->getType()->isArrayType())
754      return EmitArrayInitialization(ILE);
755
756    if (ILE->getType()->isRecordType())
757      return EmitStructInitialization(ILE);
758
759    if (ILE->getType()->isUnionType())
760      return EmitUnionInitialization(ILE);
761
762    return 0;
763  }
764
765  llvm::Constant *VisitCXXConstructExpr(CXXConstructExpr *E) {
766    if (!E->getConstructor()->isTrivial())
767      return 0;
768
769    QualType Ty = E->getType();
770
771    // FIXME: We should not have to call getBaseElementType here.
772    const RecordType *RT =
773      CGM.getContext().getBaseElementType(Ty)->getAs<RecordType>();
774    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
775
776    // If the class doesn't have a trivial destructor, we can't emit it as a
777    // constant expr.
778    if (!RD->hasTrivialDestructor())
779      return 0;
780
781    // Only copy and default constructors can be trivial.
782
783
784    if (E->getNumArgs()) {
785      assert(E->getNumArgs() == 1 && "trivial ctor with > 1 argument");
786      assert(E->getConstructor()->isCopyOrMoveConstructor() &&
787             "trivial ctor has argument but isn't a copy/move ctor");
788
789      Expr *Arg = E->getArg(0);
790      assert(CGM.getContext().hasSameUnqualifiedType(Ty, Arg->getType()) &&
791             "argument to copy ctor is of wrong type");
792
793      return Visit(Arg);
794    }
795
796    return CGM.EmitNullConstant(Ty);
797  }
798
799  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
800    return CGM.GetConstantArrayFromStringLiteral(E);
801  }
802
803  llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
804    // This must be an @encode initializing an array in a static initializer.
805    // Don't emit it as the address of the string, emit the string data itself
806    // as an inline array.
807    std::string Str;
808    CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
809    const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
810
811    // Resize the string to the right size, adding zeros at the end, or
812    // truncating as needed.
813    Str.resize(CAT->getSize().getZExtValue(), '\0');
814    return llvm::ConstantDataArray::getString(VMContext, Str, false);
815  }
816
817  llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
818    return Visit(E->getSubExpr());
819  }
820
821  // Utility methods
822  llvm::Type *ConvertType(QualType T) {
823    return CGM.getTypes().ConvertType(T);
824  }
825
826public:
827  llvm::Constant *EmitLValue(APValue::LValueBase LVBase) {
828    if (const ValueDecl *Decl = LVBase.dyn_cast<const ValueDecl*>()) {
829      if (Decl->hasAttr<WeakRefAttr>())
830        return CGM.GetWeakRefReference(Decl);
831      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
832        return CGM.GetAddrOfFunction(FD);
833      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
834        // We can never refer to a variable with local storage.
835        if (!VD->hasLocalStorage()) {
836          if (VD->isFileVarDecl() || VD->hasExternalStorage())
837            return CGM.GetAddrOfGlobalVar(VD);
838          else if (VD->isLocalVarDecl()) {
839            assert(CGF && "Can't access static local vars without CGF");
840            return CGF->GetAddrOfStaticLocalVar(VD);
841          }
842        }
843      }
844      return 0;
845    }
846
847    Expr *E = const_cast<Expr*>(LVBase.get<const Expr*>());
848    switch (E->getStmtClass()) {
849    default: break;
850    case Expr::CompoundLiteralExprClass: {
851      // Note that due to the nature of compound literals, this is guaranteed
852      // to be the only use of the variable, so we just generate it here.
853      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
854      llvm::Constant* C = CGM.EmitConstantExpr(CLE->getInitializer(),
855                                               CLE->getType(), CGF);
856      // FIXME: "Leaked" on failure.
857      if (C)
858        C = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
859                                     E->getType().isConstant(CGM.getContext()),
860                                     llvm::GlobalValue::InternalLinkage,
861                                     C, ".compoundliteral", 0, false,
862                          CGM.getContext().getTargetAddressSpace(E->getType()));
863      return C;
864    }
865    case Expr::StringLiteralClass:
866      return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
867    case Expr::ObjCEncodeExprClass:
868      return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
869    case Expr::ObjCStringLiteralClass: {
870      ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
871      llvm::Constant *C =
872          CGM.getObjCRuntime().GenerateConstantString(SL->getString());
873      return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
874    }
875    case Expr::PredefinedExprClass: {
876      unsigned Type = cast<PredefinedExpr>(E)->getIdentType();
877      if (CGF) {
878        LValue Res = CGF->EmitPredefinedLValue(cast<PredefinedExpr>(E));
879        return cast<llvm::Constant>(Res.getAddress());
880      } else if (Type == PredefinedExpr::PrettyFunction) {
881        return CGM.GetAddrOfConstantCString("top level", ".tmp");
882      }
883
884      return CGM.GetAddrOfConstantCString("", ".tmp");
885    }
886    case Expr::AddrLabelExprClass: {
887      assert(CGF && "Invalid address of label expression outside function.");
888      llvm::Constant *Ptr =
889        CGF->GetAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
890      return llvm::ConstantExpr::getBitCast(Ptr, ConvertType(E->getType()));
891    }
892    case Expr::CallExprClass: {
893      CallExpr* CE = cast<CallExpr>(E);
894      unsigned builtin = CE->isBuiltinCall();
895      if (builtin !=
896            Builtin::BI__builtin___CFStringMakeConstantString &&
897          builtin !=
898            Builtin::BI__builtin___NSStringMakeConstantString)
899        break;
900      const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
901      const StringLiteral *Literal = cast<StringLiteral>(Arg);
902      if (builtin ==
903            Builtin::BI__builtin___NSStringMakeConstantString) {
904        return CGM.getObjCRuntime().GenerateConstantString(Literal);
905      }
906      // FIXME: need to deal with UCN conversion issues.
907      return CGM.GetAddrOfConstantCFString(Literal);
908    }
909    case Expr::BlockExprClass: {
910      std::string FunctionName;
911      if (CGF)
912        FunctionName = CGF->CurFn->getName();
913      else
914        FunctionName = "global";
915
916      return CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
917    }
918    case Expr::CXXTypeidExprClass: {
919      CXXTypeidExpr *Typeid = cast<CXXTypeidExpr>(E);
920      QualType T;
921      if (Typeid->isTypeOperand())
922        T = Typeid->getTypeOperand();
923      else
924        T = Typeid->getExprOperand()->getType();
925      return CGM.GetAddrOfRTTIDescriptor(T);
926    }
927    }
928
929    return 0;
930  }
931};
932
933}  // end anonymous namespace.
934
935llvm::Constant *CodeGenModule::EmitConstantInit(const VarDecl &D,
936                                                CodeGenFunction *CGF) {
937  if (const APValue *Value = D.evaluateValue())
938    return EmitConstantValue(*Value, D.getType(), CGF);
939
940  const Expr *E = D.getInit();
941  assert(E && "No initializer to emit");
942
943  llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
944  if (C && C->getType()->isIntegerTy(1)) {
945    llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
946    C = llvm::ConstantExpr::getZExt(C, BoolTy);
947  }
948  return C;
949}
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->EvaluateAsRValue(Result, Context);
962
963  if (Success && !Result.HasSideEffects)
964    return EmitConstantValue(Result.Val, DestType, CGF);
965
966  llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
967  if (C && C->getType()->isIntegerTy(1)) {
968    llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
969    C = llvm::ConstantExpr::getZExt(C, BoolTy);
970  }
971  return C;
972}
973
974llvm::Constant *CodeGenModule::EmitConstantValue(const APValue &Value,
975                                                 QualType DestType,
976                                                 CodeGenFunction *CGF) {
977  switch (Value.getKind()) {
978  case APValue::Uninitialized:
979    llvm_unreachable("Constant expressions should be initialized.");
980  case APValue::LValue: {
981    llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
982    llvm::Constant *Offset =
983      llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext),
984                             Value.getLValueOffset().getQuantity());
985
986    llvm::Constant *C;
987    if (APValue::LValueBase LVBase = Value.getLValueBase()) {
988      // An array can be represented as an lvalue referring to the base.
989      if (isa<llvm::ArrayType>(DestTy)) {
990        assert(Offset->isNullValue() && "offset on array initializer");
991        return ConstExprEmitter(*this, CGF).Visit(
992          const_cast<Expr*>(LVBase.get<const Expr*>()));
993      }
994
995      C = ConstExprEmitter(*this, CGF).EmitLValue(LVBase);
996
997      // Apply offset if necessary.
998      if (!Offset->isNullValue()) {
999        llvm::Type *Type = llvm::Type::getInt8PtrTy(VMContext);
1000        llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
1001        Casted = llvm::ConstantExpr::getGetElementPtr(Casted, Offset);
1002        C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
1003      }
1004
1005      // Convert to the appropriate type; this could be an lvalue for
1006      // an integer.
1007      if (isa<llvm::PointerType>(DestTy))
1008        return llvm::ConstantExpr::getBitCast(C, DestTy);
1009
1010      return llvm::ConstantExpr::getPtrToInt(C, DestTy);
1011    } else {
1012      C = Offset;
1013
1014      // Convert to the appropriate type; this could be an lvalue for
1015      // an integer.
1016      if (isa<llvm::PointerType>(DestTy))
1017        return llvm::ConstantExpr::getIntToPtr(C, DestTy);
1018
1019      // If the types don't match this should only be a truncate.
1020      if (C->getType() != DestTy)
1021        return llvm::ConstantExpr::getTrunc(C, DestTy);
1022
1023      return C;
1024    }
1025  }
1026  case APValue::Int: {
1027    llvm::Constant *C = llvm::ConstantInt::get(VMContext,
1028                                               Value.getInt());
1029
1030    if (C->getType()->isIntegerTy(1)) {
1031      llvm::Type *BoolTy = getTypes().ConvertTypeForMem(DestType);
1032      C = llvm::ConstantExpr::getZExt(C, BoolTy);
1033    }
1034    return C;
1035  }
1036  case APValue::ComplexInt: {
1037    llvm::Constant *Complex[2];
1038
1039    Complex[0] = llvm::ConstantInt::get(VMContext,
1040                                        Value.getComplexIntReal());
1041    Complex[1] = llvm::ConstantInt::get(VMContext,
1042                                        Value.getComplexIntImag());
1043
1044    // FIXME: the target may want to specify that this is packed.
1045    llvm::StructType *STy = llvm::StructType::get(Complex[0]->getType(),
1046                                                  Complex[1]->getType(),
1047                                                  NULL);
1048    return llvm::ConstantStruct::get(STy, Complex);
1049  }
1050  case APValue::Float: {
1051    const llvm::APFloat &Init = Value.getFloat();
1052    if (&Init.getSemantics() == &llvm::APFloat::IEEEhalf)
1053      return llvm::ConstantInt::get(VMContext, Init.bitcastToAPInt());
1054    else
1055      return llvm::ConstantFP::get(VMContext, Init);
1056  }
1057  case APValue::ComplexFloat: {
1058    llvm::Constant *Complex[2];
1059
1060    Complex[0] = llvm::ConstantFP::get(VMContext,
1061                                       Value.getComplexFloatReal());
1062    Complex[1] = llvm::ConstantFP::get(VMContext,
1063                                       Value.getComplexFloatImag());
1064
1065    // FIXME: the target may want to specify that this is packed.
1066    llvm::StructType *STy = llvm::StructType::get(Complex[0]->getType(),
1067                                                  Complex[1]->getType(),
1068                                                  NULL);
1069    return llvm::ConstantStruct::get(STy, Complex);
1070  }
1071  case APValue::Vector: {
1072    SmallVector<llvm::Constant *, 4> Inits;
1073    unsigned NumElts = Value.getVectorLength();
1074
1075    for (unsigned i = 0; i != NumElts; ++i) {
1076      const APValue &Elt = Value.getVectorElt(i);
1077      if (Elt.isInt())
1078        Inits.push_back(llvm::ConstantInt::get(VMContext, Elt.getInt()));
1079      else
1080        Inits.push_back(llvm::ConstantFP::get(VMContext, Elt.getFloat()));
1081    }
1082    return llvm::ConstantVector::get(Inits);
1083  }
1084  case APValue::AddrLabelDiff: {
1085    const AddrLabelExpr *LHSExpr = Value.getAddrLabelDiffLHS();
1086    const AddrLabelExpr *RHSExpr = Value.getAddrLabelDiffRHS();
1087    llvm::Constant *LHS = EmitConstantExpr(LHSExpr, LHSExpr->getType(), CGF);
1088    llvm::Constant *RHS = EmitConstantExpr(RHSExpr, RHSExpr->getType(), CGF);
1089
1090    // Compute difference
1091    llvm::Type *ResultType = getTypes().ConvertType(DestType);
1092    LHS = llvm::ConstantExpr::getPtrToInt(LHS, IntPtrTy);
1093    RHS = llvm::ConstantExpr::getPtrToInt(RHS, IntPtrTy);
1094    llvm::Constant *AddrLabelDiff = llvm::ConstantExpr::getSub(LHS, RHS);
1095
1096    // LLVM is a bit sensitive about the exact format of the
1097    // address-of-label difference; make sure to truncate after
1098    // the subtraction.
1099    return llvm::ConstantExpr::getTruncOrBitCast(AddrLabelDiff, ResultType);
1100  }
1101  case APValue::Struct:
1102  case APValue::Union:
1103    return ConstStructBuilder::BuildStruct(*this, CGF, Value, DestType);
1104  case APValue::Array: {
1105    const ArrayType *CAT = Context.getAsArrayType(DestType);
1106    unsigned NumElements = Value.getArraySize();
1107    unsigned NumInitElts = Value.getArrayInitializedElts();
1108
1109    std::vector<llvm::Constant*> Elts;
1110    Elts.reserve(NumElements);
1111
1112    // Emit array filler, if there is one.
1113    llvm::Constant *Filler = 0;
1114    if (Value.hasArrayFiller())
1115      Filler = EmitConstantValue(Value.getArrayFiller(),
1116                                 CAT->getElementType(), CGF);
1117
1118    // Emit initializer elements.
1119    llvm::Type *CommonElementType = 0;
1120    for (unsigned I = 0; I < NumElements; ++I) {
1121      llvm::Constant *C = Filler;
1122      if (I < NumInitElts)
1123        C = EmitConstantValue(Value.getArrayInitializedElt(I),
1124                              CAT->getElementType(), CGF);
1125      if (I == 0)
1126        CommonElementType = C->getType();
1127      else if (C->getType() != CommonElementType)
1128        CommonElementType = 0;
1129      Elts.push_back(C);
1130    }
1131
1132    if (!CommonElementType) {
1133      // FIXME: Try to avoid packing the array
1134      std::vector<llvm::Type*> Types;
1135      for (unsigned i = 0, e = Elts.size(); i < e; ++i)
1136        Types.push_back(Elts[i]->getType());
1137      llvm::StructType *SType = llvm::StructType::get(VMContext, Types, true);
1138      return llvm::ConstantStruct::get(SType, Elts);
1139    }
1140
1141    llvm::ArrayType *AType =
1142      llvm::ArrayType::get(CommonElementType, NumElements);
1143    return llvm::ConstantArray::get(AType, Elts);
1144  }
1145  case APValue::MemberPointer:
1146    return getCXXABI().EmitMemberPointer(Value, DestType);
1147  }
1148  llvm_unreachable("Unknown APValue kind");
1149}
1150
1151llvm::Constant *
1152CodeGenModule::GetAddrOfConstantCompoundLiteral(const CompoundLiteralExpr *E) {
1153  assert(E->isFileScope() && "not a file-scope compound literal expr");
1154  return ConstExprEmitter(*this, 0).EmitLValue(E);
1155}
1156
1157llvm::Constant *
1158CodeGenModule::getMemberPointerConstant(const UnaryOperator *uo) {
1159  // Member pointer constants always have a very particular form.
1160  const MemberPointerType *type = cast<MemberPointerType>(uo->getType());
1161  const ValueDecl *decl = cast<DeclRefExpr>(uo->getSubExpr())->getDecl();
1162
1163  // A member function pointer.
1164  if (const CXXMethodDecl *method = dyn_cast<CXXMethodDecl>(decl))
1165    return getCXXABI().EmitMemberPointer(method);
1166
1167  // Otherwise, a member data pointer.
1168  uint64_t fieldOffset = getContext().getFieldOffset(decl);
1169  CharUnits chars = getContext().toCharUnitsFromBits((int64_t) fieldOffset);
1170  return getCXXABI().EmitMemberDataPointer(type, chars);
1171}
1172
1173static void
1174FillInNullDataMemberPointers(CodeGenModule &CGM, QualType T,
1175                             SmallVectorImpl<llvm::Constant *> &Elements,
1176                             uint64_t StartOffset) {
1177  assert(StartOffset % CGM.getContext().getCharWidth() == 0 &&
1178         "StartOffset not byte aligned!");
1179
1180  if (CGM.getTypes().isZeroInitializable(T))
1181    return;
1182
1183  if (const ConstantArrayType *CAT =
1184        CGM.getContext().getAsConstantArrayType(T)) {
1185    QualType ElementTy = CAT->getElementType();
1186    uint64_t ElementSize = CGM.getContext().getTypeSize(ElementTy);
1187
1188    for (uint64_t I = 0, E = CAT->getSize().getZExtValue(); I != E; ++I) {
1189      FillInNullDataMemberPointers(CGM, ElementTy, Elements,
1190                                   StartOffset + I * ElementSize);
1191    }
1192  } else if (const RecordType *RT = T->getAs<RecordType>()) {
1193    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
1194    const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
1195
1196    // Go through all bases and fill in any null pointer to data members.
1197    for (CXXRecordDecl::base_class_const_iterator I = RD->bases_begin(),
1198         E = RD->bases_end(); I != E; ++I) {
1199      if (I->isVirtual()) {
1200        // Ignore virtual bases.
1201        continue;
1202      }
1203
1204      const CXXRecordDecl *BaseDecl =
1205      cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());
1206
1207      // Ignore empty bases.
1208      if (BaseDecl->isEmpty())
1209        continue;
1210
1211      // Ignore bases that don't have any pointer to data members.
1212      if (CGM.getTypes().isZeroInitializable(BaseDecl))
1213        continue;
1214
1215      uint64_t BaseOffset = Layout.getBaseClassOffsetInBits(BaseDecl);
1216      FillInNullDataMemberPointers(CGM, I->getType(),
1217                                   Elements, StartOffset + BaseOffset);
1218    }
1219
1220    // Visit all fields.
1221    unsigned FieldNo = 0;
1222    for (RecordDecl::field_iterator I = RD->field_begin(),
1223         E = RD->field_end(); I != E; ++I, ++FieldNo) {
1224      QualType FieldType = I->getType();
1225
1226      if (CGM.getTypes().isZeroInitializable(FieldType))
1227        continue;
1228
1229      uint64_t FieldOffset = StartOffset + Layout.getFieldOffset(FieldNo);
1230      FillInNullDataMemberPointers(CGM, FieldType, Elements, FieldOffset);
1231    }
1232  } else {
1233    assert(T->isMemberPointerType() && "Should only see member pointers here!");
1234    assert(!T->getAs<MemberPointerType>()->getPointeeType()->isFunctionType() &&
1235           "Should only see pointers to data members here!");
1236
1237    CharUnits StartIndex = CGM.getContext().toCharUnitsFromBits(StartOffset);
1238    CharUnits EndIndex = StartIndex + CGM.getContext().getTypeSizeInChars(T);
1239
1240    // FIXME: hardcodes Itanium member pointer representation!
1241    llvm::Constant *NegativeOne =
1242      llvm::ConstantInt::get(llvm::Type::getInt8Ty(CGM.getLLVMContext()),
1243                             -1ULL, /*isSigned*/true);
1244
1245    // Fill in the null data member pointer.
1246    for (CharUnits I = StartIndex; I != EndIndex; ++I)
1247      Elements[I.getQuantity()] = NegativeOne;
1248  }
1249}
1250
1251static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
1252                                               llvm::Type *baseType,
1253                                               const CXXRecordDecl *base);
1254
1255static llvm::Constant *EmitNullConstant(CodeGenModule &CGM,
1256                                        const CXXRecordDecl *record,
1257                                        bool asCompleteObject) {
1258  const CGRecordLayout &layout = CGM.getTypes().getCGRecordLayout(record);
1259  llvm::StructType *structure =
1260    (asCompleteObject ? layout.getLLVMType()
1261                      : layout.getBaseSubobjectLLVMType());
1262
1263  unsigned numElements = structure->getNumElements();
1264  std::vector<llvm::Constant *> elements(numElements);
1265
1266  // Fill in all the bases.
1267  for (CXXRecordDecl::base_class_const_iterator
1268         I = record->bases_begin(), E = record->bases_end(); I != E; ++I) {
1269    if (I->isVirtual()) {
1270      // Ignore virtual bases; if we're laying out for a complete
1271      // object, we'll lay these out later.
1272      continue;
1273    }
1274
1275    const CXXRecordDecl *base =
1276      cast<CXXRecordDecl>(I->getType()->castAs<RecordType>()->getDecl());
1277
1278    // Ignore empty bases.
1279    if (base->isEmpty())
1280      continue;
1281
1282    unsigned fieldIndex = layout.getNonVirtualBaseLLVMFieldNo(base);
1283    llvm::Type *baseType = structure->getElementType(fieldIndex);
1284    elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
1285  }
1286
1287  // Fill in all the fields.
1288  for (RecordDecl::field_iterator I = record->field_begin(),
1289         E = record->field_end(); I != E; ++I) {
1290    const FieldDecl *field = *I;
1291
1292    // Fill in non-bitfields. (Bitfields always use a zero pattern, which we
1293    // will fill in later.)
1294    if (!field->isBitField()) {
1295      unsigned fieldIndex = layout.getLLVMFieldNo(field);
1296      elements[fieldIndex] = CGM.EmitNullConstant(field->getType());
1297    }
1298
1299    // For unions, stop after the first named field.
1300    if (record->isUnion() && field->getDeclName())
1301      break;
1302  }
1303
1304  // Fill in the virtual bases, if we're working with the complete object.
1305  if (asCompleteObject) {
1306    for (CXXRecordDecl::base_class_const_iterator
1307           I = record->vbases_begin(), E = record->vbases_end(); I != E; ++I) {
1308      const CXXRecordDecl *base =
1309        cast<CXXRecordDecl>(I->getType()->castAs<RecordType>()->getDecl());
1310
1311      // Ignore empty bases.
1312      if (base->isEmpty())
1313        continue;
1314
1315      unsigned fieldIndex = layout.getVirtualBaseIndex(base);
1316
1317      // We might have already laid this field out.
1318      if (elements[fieldIndex]) continue;
1319
1320      llvm::Type *baseType = structure->getElementType(fieldIndex);
1321      elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
1322    }
1323  }
1324
1325  // Now go through all other fields and zero them out.
1326  for (unsigned i = 0; i != numElements; ++i) {
1327    if (!elements[i])
1328      elements[i] = llvm::Constant::getNullValue(structure->getElementType(i));
1329  }
1330
1331  return llvm::ConstantStruct::get(structure, elements);
1332}
1333
1334/// Emit the null constant for a base subobject.
1335static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
1336                                               llvm::Type *baseType,
1337                                               const CXXRecordDecl *base) {
1338  const CGRecordLayout &baseLayout = CGM.getTypes().getCGRecordLayout(base);
1339
1340  // Just zero out bases that don't have any pointer to data members.
1341  if (baseLayout.isZeroInitializableAsBase())
1342    return llvm::Constant::getNullValue(baseType);
1343
1344  // If the base type is a struct, we can just use its null constant.
1345  if (isa<llvm::StructType>(baseType)) {
1346    return EmitNullConstant(CGM, base, /*complete*/ false);
1347  }
1348
1349  // Otherwise, some bases are represented as arrays of i8 if the size
1350  // of the base is smaller than its corresponding LLVM type.  Figure
1351  // out how many elements this base array has.
1352  llvm::ArrayType *baseArrayType = cast<llvm::ArrayType>(baseType);
1353  unsigned numBaseElements = baseArrayType->getNumElements();
1354
1355  // Fill in null data member pointers.
1356  SmallVector<llvm::Constant *, 16> baseElements(numBaseElements);
1357  FillInNullDataMemberPointers(CGM, CGM.getContext().getTypeDeclType(base),
1358                               baseElements, 0);
1359
1360  // Now go through all other elements and zero them out.
1361  if (numBaseElements) {
1362    llvm::Type *i8 = llvm::Type::getInt8Ty(CGM.getLLVMContext());
1363    llvm::Constant *i8_zero = llvm::Constant::getNullValue(i8);
1364    for (unsigned i = 0; i != numBaseElements; ++i) {
1365      if (!baseElements[i])
1366        baseElements[i] = i8_zero;
1367    }
1368  }
1369
1370  return llvm::ConstantArray::get(baseArrayType, baseElements);
1371}
1372
1373llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
1374  if (getTypes().isZeroInitializable(T))
1375    return llvm::Constant::getNullValue(getTypes().ConvertTypeForMem(T));
1376
1377  if (const ConstantArrayType *CAT = Context.getAsConstantArrayType(T)) {
1378    llvm::ArrayType *ATy =
1379      cast<llvm::ArrayType>(getTypes().ConvertTypeForMem(T));
1380
1381    QualType ElementTy = CAT->getElementType();
1382
1383    llvm::Constant *Element = EmitNullConstant(ElementTy);
1384    unsigned NumElements = CAT->getSize().getZExtValue();
1385
1386    if (Element->isNullValue())
1387      return llvm::ConstantAggregateZero::get(ATy);
1388
1389    SmallVector<llvm::Constant *, 8> Array(NumElements, Element);
1390    return llvm::ConstantArray::get(ATy, Array);
1391  }
1392
1393  if (const RecordType *RT = T->getAs<RecordType>()) {
1394    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
1395    return ::EmitNullConstant(*this, RD, /*complete object*/ true);
1396  }
1397
1398  assert(T->isMemberPointerType() && "Should only see member pointers here!");
1399  assert(!T->getAs<MemberPointerType>()->getPointeeType()->isFunctionType() &&
1400         "Should only see pointers to data members here!");
1401
1402  // Itanium C++ ABI 2.3:
1403  //   A NULL pointer is represented as -1.
1404  return getCXXABI().EmitNullMemberPointer(T->castAs<MemberPointerType>());
1405}
1406
1407llvm::Constant *
1408CodeGenModule::EmitNullConstantForBase(const CXXRecordDecl *Record) {
1409  return ::EmitNullConstant(*this, Record, false);
1410}
1411