CGExprConstant.cpp revision cdb30b41590bf9e20d1d46a866fce071ebadf21a 
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 "CGObjCRuntime.h"
17#include "CGRecordLayout.h"
18#include "clang/AST/APValue.h"
19#include "clang/AST/ASTContext.h"
20#include "clang/AST/RecordLayout.h"
21#include "clang/AST/StmtVisitor.h"
22#include "clang/Basic/Builtins.h"
23#include "llvm/Constants.h"
24#include "llvm/Function.h"
25#include "llvm/GlobalVariable.h"
26#include "llvm/Target/TargetData.h"
27using namespace clang;
28using namespace CodeGen;
29
30//===----------------------------------------------------------------------===//
31//                            ConstStructBuilder
32//===----------------------------------------------------------------------===//
33
34namespace {
35class ConstStructBuilder {
36  CodeGenModule &CGM;
37  CodeGenFunction *CGF;
38
39  bool Packed;
40  unsigned NextFieldOffsetInBytes;
41  unsigned LLVMStructAlignment;
42  std::vector<llvm::Constant *> Elements;
43public:
44  static llvm::Constant *BuildStruct(CodeGenModule &CGM, CodeGenFunction *CGF,
45                                     InitListExpr *ILE);
46
47private:
48  ConstStructBuilder(CodeGenModule &CGM, CodeGenFunction *CGF)
49    : CGM(CGM), CGF(CGF), Packed(false), NextFieldOffsetInBytes(0),
50    LLVMStructAlignment(1) { }
51
52  bool AppendField(const FieldDecl *Field, uint64_t FieldOffset,
53                   llvm::Constant *InitExpr);
54
55  bool AppendBitField(const FieldDecl *Field, uint64_t FieldOffset,
56                      llvm::Constant *InitExpr);
57
58  void AppendPadding(uint64_t NumBytes);
59
60  void AppendTailPadding(uint64_t RecordSize);
61
62  void ConvertStructToPacked();
63
64  bool Build(InitListExpr *ILE);
65
66  unsigned getAlignment(const llvm::Constant *C) const {
67    if (Packed)  return 1;
68    return CGM.getTargetData().getABITypeAlignment(C->getType());
69  }
70
71  uint64_t getSizeInBytes(const llvm::Constant *C) const {
72    return CGM.getTargetData().getTypeAllocSize(C->getType());
73  }
74};
75
76bool ConstStructBuilder::
77AppendField(const FieldDecl *Field, uint64_t FieldOffset,
78            llvm::Constant *InitCst) {
79  uint64_t FieldOffsetInBytes = FieldOffset / 8;
80
81  assert(NextFieldOffsetInBytes <= FieldOffsetInBytes
82         && "Field offset mismatch!");
83
84  // Emit the field.
85  if (!InitCst)
86    return false;
87
88  unsigned FieldAlignment = getAlignment(InitCst);
89
90  // Round up the field offset to the alignment of the field type.
91  uint64_t AlignedNextFieldOffsetInBytes =
92    llvm::RoundUpToAlignment(NextFieldOffsetInBytes, FieldAlignment);
93
94  if (AlignedNextFieldOffsetInBytes > FieldOffsetInBytes) {
95    assert(!Packed && "Alignment is wrong even with a packed struct!");
96
97    // Convert the struct to a packed struct.
98    ConvertStructToPacked();
99
100    AlignedNextFieldOffsetInBytes = NextFieldOffsetInBytes;
101  }
102
103  if (AlignedNextFieldOffsetInBytes < FieldOffsetInBytes) {
104    // We need to append padding.
105    AppendPadding(FieldOffsetInBytes - NextFieldOffsetInBytes);
106
107    assert(NextFieldOffsetInBytes == FieldOffsetInBytes &&
108           "Did not add enough padding!");
109
110    AlignedNextFieldOffsetInBytes = NextFieldOffsetInBytes;
111  }
112
113  // Add the field.
114  Elements.push_back(InitCst);
115  NextFieldOffsetInBytes = AlignedNextFieldOffsetInBytes +
116                             getSizeInBytes(InitCst);
117
118  if (Packed)
119    assert(LLVMStructAlignment == 1 && "Packed struct not byte-aligned!");
120  else
121    LLVMStructAlignment = std::max(LLVMStructAlignment, FieldAlignment);
122
123  return true;
124}
125
126bool ConstStructBuilder::
127  AppendBitField(const FieldDecl *Field, uint64_t FieldOffset,
128                 llvm::Constant *InitCst) {
129  llvm::ConstantInt *CI = cast_or_null<llvm::ConstantInt>(InitCst);
130  // FIXME: Can this ever happen?
131  if (!CI)
132    return false;
133
134  if (FieldOffset > NextFieldOffsetInBytes * 8) {
135    // We need to add padding.
136    uint64_t NumBytes =
137      llvm::RoundUpToAlignment(FieldOffset -
138                               NextFieldOffsetInBytes * 8, 8) / 8;
139
140    AppendPadding(NumBytes);
141  }
142
143  uint64_t FieldSize =
144    Field->getBitWidth()->EvaluateAsInt(CGM.getContext()).getZExtValue();
145
146  llvm::APInt FieldValue = CI->getValue();
147
148  // Promote the size of FieldValue if necessary
149  // FIXME: This should never occur, but currently it can because initializer
150  // constants are cast to bool, and because clang is not enforcing bitfield
151  // width limits.
152  if (FieldSize > FieldValue.getBitWidth())
153    FieldValue.zext(FieldSize);
154
155  // Truncate the size of FieldValue to the bit field size.
156  if (FieldSize < FieldValue.getBitWidth())
157    FieldValue.trunc(FieldSize);
158
159  if (FieldOffset < NextFieldOffsetInBytes * 8) {
160    // Either part of the field or the entire field can go into the previous
161    // byte.
162    assert(!Elements.empty() && "Elements can't be empty!");
163
164    unsigned BitsInPreviousByte =
165      NextFieldOffsetInBytes * 8 - FieldOffset;
166
167    bool FitsCompletelyInPreviousByte =
168      BitsInPreviousByte >= FieldValue.getBitWidth();
169
170    llvm::APInt Tmp = FieldValue;
171
172    if (!FitsCompletelyInPreviousByte) {
173      unsigned NewFieldWidth = FieldSize - BitsInPreviousByte;
174
175      if (CGM.getTargetData().isBigEndian()) {
176        Tmp = Tmp.lshr(NewFieldWidth);
177        Tmp.trunc(BitsInPreviousByte);
178
179        // We want the remaining high bits.
180        FieldValue.trunc(NewFieldWidth);
181      } else {
182        Tmp.trunc(BitsInPreviousByte);
183
184        // We want the remaining low bits.
185        FieldValue = FieldValue.lshr(BitsInPreviousByte);
186        FieldValue.trunc(NewFieldWidth);
187      }
188    }
189
190    Tmp.zext(8);
191    if (CGM.getTargetData().isBigEndian()) {
192      if (FitsCompletelyInPreviousByte)
193        Tmp = Tmp.shl(BitsInPreviousByte - FieldValue.getBitWidth());
194    } else {
195      Tmp = Tmp.shl(8 - BitsInPreviousByte);
196    }
197
198    // Or in the bits that go into the previous byte.
199    if (llvm::ConstantInt *Val = dyn_cast<llvm::ConstantInt>(Elements.back()))
200      Tmp |= Val->getValue();
201    else
202      assert(isa<llvm::UndefValue>(Elements.back()));
203
204    Elements.back() = llvm::ConstantInt::get(CGM.getLLVMContext(), Tmp);
205
206    if (FitsCompletelyInPreviousByte)
207      return true;
208  }
209
210  while (FieldValue.getBitWidth() > 8) {
211    llvm::APInt Tmp;
212
213    if (CGM.getTargetData().isBigEndian()) {
214      // We want the high bits.
215      Tmp = FieldValue;
216      Tmp = Tmp.lshr(Tmp.getBitWidth() - 8);
217      Tmp.trunc(8);
218    } else {
219      // We want the low bits.
220      Tmp = FieldValue;
221      Tmp.trunc(8);
222
223      FieldValue = FieldValue.lshr(8);
224    }
225
226    Elements.push_back(llvm::ConstantInt::get(CGM.getLLVMContext(), Tmp));
227    NextFieldOffsetInBytes++;
228
229    FieldValue.trunc(FieldValue.getBitWidth() - 8);
230  }
231
232  assert(FieldValue.getBitWidth() > 0 &&
233         "Should have at least one bit left!");
234  assert(FieldValue.getBitWidth() <= 8 &&
235         "Should not have more than a byte left!");
236
237  if (FieldValue.getBitWidth() < 8) {
238    if (CGM.getTargetData().isBigEndian()) {
239      unsigned BitWidth = FieldValue.getBitWidth();
240
241      FieldValue.zext(8);
242      FieldValue = FieldValue << (8 - BitWidth);
243    } else
244      FieldValue.zext(8);
245  }
246
247  // Append the last element.
248  Elements.push_back(llvm::ConstantInt::get(CGM.getLLVMContext(),
249                                            FieldValue));
250  NextFieldOffsetInBytes++;
251  return true;
252}
253
254void ConstStructBuilder::AppendPadding(uint64_t NumBytes) {
255  if (!NumBytes)
256    return;
257
258  const llvm::Type *Ty = llvm::Type::getInt8Ty(CGM.getLLVMContext());
259  if (NumBytes > 1)
260    Ty = llvm::ArrayType::get(Ty, NumBytes);
261
262  llvm::Constant *C = llvm::UndefValue::get(Ty);
263  Elements.push_back(C);
264  assert(getAlignment(C) == 1 && "Padding must have 1 byte alignment!");
265
266  NextFieldOffsetInBytes += getSizeInBytes(C);
267}
268
269void ConstStructBuilder::AppendTailPadding(uint64_t RecordSize) {
270  assert(RecordSize % 8 == 0 && "Invalid record size!");
271
272  uint64_t RecordSizeInBytes = RecordSize / 8;
273  assert(NextFieldOffsetInBytes <= RecordSizeInBytes && "Size mismatch!");
274
275  unsigned NumPadBytes = RecordSizeInBytes - NextFieldOffsetInBytes;
276  AppendPadding(NumPadBytes);
277}
278
279void ConstStructBuilder::ConvertStructToPacked() {
280  std::vector<llvm::Constant *> PackedElements;
281  uint64_t ElementOffsetInBytes = 0;
282
283  for (unsigned i = 0, e = Elements.size(); i != e; ++i) {
284    llvm::Constant *C = Elements[i];
285
286    unsigned ElementAlign =
287      CGM.getTargetData().getABITypeAlignment(C->getType());
288    uint64_t AlignedElementOffsetInBytes =
289      llvm::RoundUpToAlignment(ElementOffsetInBytes, ElementAlign);
290
291    if (AlignedElementOffsetInBytes > ElementOffsetInBytes) {
292      // We need some padding.
293      uint64_t NumBytes =
294        AlignedElementOffsetInBytes - ElementOffsetInBytes;
295
296      const llvm::Type *Ty = llvm::Type::getInt8Ty(CGM.getLLVMContext());
297      if (NumBytes > 1)
298        Ty = llvm::ArrayType::get(Ty, NumBytes);
299
300      llvm::Constant *Padding = llvm::UndefValue::get(Ty);
301      PackedElements.push_back(Padding);
302      ElementOffsetInBytes += getSizeInBytes(Padding);
303    }
304
305    PackedElements.push_back(C);
306    ElementOffsetInBytes += getSizeInBytes(C);
307  }
308
309  assert(ElementOffsetInBytes == NextFieldOffsetInBytes &&
310         "Packing the struct changed its size!");
311
312  Elements = PackedElements;
313  LLVMStructAlignment = 1;
314  Packed = true;
315}
316
317bool ConstStructBuilder::Build(InitListExpr *ILE) {
318  RecordDecl *RD = ILE->getType()->getAs<RecordType>()->getDecl();
319  const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
320
321  unsigned FieldNo = 0;
322  unsigned ElementNo = 0;
323  for (RecordDecl::field_iterator Field = RD->field_begin(),
324       FieldEnd = RD->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
325
326    // If this is a union, skip all the fields that aren't being initialized.
327    if (RD->isUnion() && ILE->getInitializedFieldInUnion() != *Field)
328      continue;
329
330    // Don't emit anonymous bitfields, they just affect layout.
331    if (Field->isBitField() && !Field->getIdentifier())
332      continue;
333
334    // Get the initializer.  A struct can include fields without initializers,
335    // we just use explicit null values for them.
336    llvm::Constant *EltInit;
337    if (ElementNo < ILE->getNumInits())
338      EltInit = CGM.EmitConstantExpr(ILE->getInit(ElementNo++),
339                                     Field->getType(), CGF);
340    else
341      EltInit = CGM.EmitNullConstant(Field->getType());
342
343    if (!Field->isBitField()) {
344      // Handle non-bitfield members.
345      if (!AppendField(*Field, Layout.getFieldOffset(FieldNo), EltInit))
346        return false;
347    } else {
348      // Otherwise we have a bitfield.
349      if (!AppendBitField(*Field, Layout.getFieldOffset(FieldNo), EltInit))
350        return false;
351    }
352  }
353
354  uint64_t LayoutSizeInBytes = Layout.getSize() / 8;
355
356  if (NextFieldOffsetInBytes > LayoutSizeInBytes) {
357    // If the struct is bigger than the size of the record type,
358    // we must have a flexible array member at the end.
359    assert(RD->hasFlexibleArrayMember() &&
360           "Must have flexible array member if struct is bigger than type!");
361
362    // No tail padding is necessary.
363    return true;
364  }
365
366  uint64_t LLVMSizeInBytes = llvm::RoundUpToAlignment(NextFieldOffsetInBytes,
367                                                      LLVMStructAlignment);
368
369  // Check if we need to convert the struct to a packed struct.
370  if (NextFieldOffsetInBytes <= LayoutSizeInBytes &&
371      LLVMSizeInBytes > LayoutSizeInBytes) {
372    assert(!Packed && "Size mismatch!");
373
374    ConvertStructToPacked();
375    assert(NextFieldOffsetInBytes == LayoutSizeInBytes &&
376           "Converting to packed did not help!");
377  }
378
379  // Append tail padding if necessary.
380  AppendTailPadding(Layout.getSize());
381
382  assert(Layout.getSize() / 8 == NextFieldOffsetInBytes &&
383         "Tail padding mismatch!");
384
385  return true;
386}
387
388llvm::Constant *ConstStructBuilder::
389  BuildStruct(CodeGenModule &CGM, CodeGenFunction *CGF, InitListExpr *ILE) {
390  ConstStructBuilder Builder(CGM, CGF);
391
392  if (!Builder.Build(ILE))
393    return 0;
394
395  llvm::Constant *Result =
396  llvm::ConstantStruct::get(CGM.getLLVMContext(),
397                            Builder.Elements, Builder.Packed);
398
399  assert(llvm::RoundUpToAlignment(Builder.NextFieldOffsetInBytes,
400                                  Builder.getAlignment(Result)) ==
401         Builder.getSizeInBytes(Result) && "Size mismatch!");
402
403  return Result;
404}
405
406
407//===----------------------------------------------------------------------===//
408//                             ConstExprEmitter
409//===----------------------------------------------------------------------===//
410
411class ConstExprEmitter :
412  public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
413  CodeGenModule &CGM;
414  CodeGenFunction *CGF;
415  llvm::LLVMContext &VMContext;
416public:
417  ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
418    : CGM(cgm), CGF(cgf), VMContext(cgm.getLLVMContext()) {
419  }
420
421  //===--------------------------------------------------------------------===//
422  //                            Visitor Methods
423  //===--------------------------------------------------------------------===//
424
425  llvm::Constant *VisitStmt(Stmt *S) {
426    return 0;
427  }
428
429  llvm::Constant *VisitParenExpr(ParenExpr *PE) {
430    return Visit(PE->getSubExpr());
431  }
432
433  llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
434    return Visit(E->getInitializer());
435  }
436
437  llvm::Constant *EmitMemberFunctionPointer(CXXMethodDecl *MD) {
438    assert(MD->isInstance() && "Member function must not be static!");
439
440    MD = MD->getCanonicalDecl();
441
442    const llvm::Type *PtrDiffTy =
443      CGM.getTypes().ConvertType(CGM.getContext().getPointerDiffType());
444
445    llvm::Constant *Values[2];
446
447    // Get the function pointer (or index if this is a virtual function).
448    if (MD->isVirtual()) {
449      uint64_t Index = CGM.getVTables().getMethodVtableIndex(MD);
450
451      // Itanium C++ ABI 2.3:
452      //   For a non-virtual function, this field is a simple function pointer.
453      //   For a virtual function, it is 1 plus the virtual table offset
454      //   (in bytes) of the function, represented as a ptrdiff_t.
455      Values[0] = llvm::ConstantInt::get(PtrDiffTy, (Index * 8) + 1);
456    } else {
457      const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
458      const llvm::Type *Ty =
459        CGM.getTypes().GetFunctionType(CGM.getTypes().getFunctionInfo(MD),
460                                       FPT->isVariadic());
461
462      llvm::Constant *FuncPtr = CGM.GetAddrOfFunction(MD, Ty);
463      Values[0] = llvm::ConstantExpr::getPtrToInt(FuncPtr, PtrDiffTy);
464    }
465
466    // The adjustment will always be 0.
467    Values[1] = llvm::ConstantInt::get(PtrDiffTy, 0);
468
469    return llvm::ConstantStruct::get(CGM.getLLVMContext(),
470                                     Values, 2, /*Packed=*/false);
471  }
472
473  llvm::Constant *VisitUnaryAddrOf(UnaryOperator *E) {
474    if (const MemberPointerType *MPT =
475        E->getType()->getAs<MemberPointerType>()) {
476      QualType T = MPT->getPointeeType();
477      DeclRefExpr *DRE = cast<DeclRefExpr>(E->getSubExpr());
478
479      NamedDecl *ND = DRE->getDecl();
480      if (T->isFunctionProtoType())
481        return EmitMemberFunctionPointer(cast<CXXMethodDecl>(ND));
482
483      // We have a pointer to data member.
484      return CGM.EmitPointerToDataMember(cast<FieldDecl>(ND));
485    }
486
487    return 0;
488  }
489
490  llvm::Constant *VisitBinSub(BinaryOperator *E) {
491    // This must be a pointer/pointer subtraction.  This only happens for
492    // address of label.
493    if (!isa<AddrLabelExpr>(E->getLHS()->IgnoreParenNoopCasts(CGM.getContext())) ||
494       !isa<AddrLabelExpr>(E->getRHS()->IgnoreParenNoopCasts(CGM.getContext())))
495      return 0;
496
497    llvm::Constant *LHS = CGM.EmitConstantExpr(E->getLHS(),
498                                               E->getLHS()->getType(), CGF);
499    llvm::Constant *RHS = CGM.EmitConstantExpr(E->getRHS(),
500                                               E->getRHS()->getType(), CGF);
501
502    const llvm::Type *ResultType = ConvertType(E->getType());
503    LHS = llvm::ConstantExpr::getPtrToInt(LHS, ResultType);
504    RHS = llvm::ConstantExpr::getPtrToInt(RHS, ResultType);
505
506    // No need to divide by element size, since addr of label is always void*,
507    // which has size 1 in GNUish.
508    return llvm::ConstantExpr::getSub(LHS, RHS);
509  }
510
511  llvm::Constant *VisitCastExpr(CastExpr* E) {
512    switch (E->getCastKind()) {
513    case CastExpr::CK_ToUnion: {
514      // GCC cast to union extension
515      assert(E->getType()->isUnionType() &&
516             "Destination type is not union type!");
517      const llvm::Type *Ty = ConvertType(E->getType());
518      Expr *SubExpr = E->getSubExpr();
519
520      llvm::Constant *C =
521        CGM.EmitConstantExpr(SubExpr, SubExpr->getType(), CGF);
522      if (!C)
523        return 0;
524
525      // Build a struct with the union sub-element as the first member,
526      // and padded to the appropriate size
527      std::vector<llvm::Constant*> Elts;
528      std::vector<const llvm::Type*> Types;
529      Elts.push_back(C);
530      Types.push_back(C->getType());
531      unsigned CurSize = CGM.getTargetData().getTypeAllocSize(C->getType());
532      unsigned TotalSize = CGM.getTargetData().getTypeAllocSize(Ty);
533
534      assert(CurSize <= TotalSize && "Union size mismatch!");
535      if (unsigned NumPadBytes = TotalSize - CurSize) {
536        const llvm::Type *Ty = llvm::Type::getInt8Ty(VMContext);
537        if (NumPadBytes > 1)
538          Ty = llvm::ArrayType::get(Ty, NumPadBytes);
539
540        Elts.push_back(llvm::UndefValue::get(Ty));
541        Types.push_back(Ty);
542      }
543
544      llvm::StructType* STy =
545        llvm::StructType::get(C->getType()->getContext(), Types, false);
546      return llvm::ConstantStruct::get(STy, Elts);
547    }
548    case CastExpr::CK_NullToMemberPointer:
549      return CGM.EmitNullConstant(E->getType());
550
551    case CastExpr::CK_BaseToDerivedMemberPointer: {
552      Expr *SubExpr = E->getSubExpr();
553
554      const MemberPointerType *SrcTy =
555        SubExpr->getType()->getAs<MemberPointerType>();
556      const MemberPointerType *DestTy =
557        E->getType()->getAs<MemberPointerType>();
558
559      const CXXRecordDecl *BaseClass =
560        cast<CXXRecordDecl>(cast<RecordType>(SrcTy->getClass())->getDecl());
561      const CXXRecordDecl *DerivedClass =
562        cast<CXXRecordDecl>(cast<RecordType>(DestTy->getClass())->getDecl());
563
564      if (SrcTy->getPointeeType()->isFunctionProtoType()) {
565        llvm::Constant *C =
566          CGM.EmitConstantExpr(SubExpr, SubExpr->getType(), CGF);
567        if (!C)
568          return 0;
569
570        llvm::ConstantStruct *CS = cast<llvm::ConstantStruct>(C);
571
572        // Check if we need to update the adjustment.
573        if (llvm::Constant *Offset =
574              CGM.GetNonVirtualBaseClassOffset(DerivedClass, BaseClass)) {
575          llvm::Constant *Values[2];
576
577          Values[0] = CS->getOperand(0);
578          Values[1] = llvm::ConstantExpr::getAdd(CS->getOperand(1), Offset);
579          return llvm::ConstantStruct::get(CGM.getLLVMContext(), Values, 2,
580                                           /*Packed=*/false);
581        }
582
583        return CS;
584      }
585    }
586
587    case CastExpr::CK_BitCast:
588      // This must be a member function pointer cast.
589      return Visit(E->getSubExpr());
590
591    default: {
592      // FIXME: This should be handled by the CK_NoOp cast kind.
593      // Explicit and implicit no-op casts
594      QualType Ty = E->getType(), SubTy = E->getSubExpr()->getType();
595      if (CGM.getContext().hasSameUnqualifiedType(Ty, SubTy))
596        return Visit(E->getSubExpr());
597
598      // Handle integer->integer casts for address-of-label differences.
599      if (Ty->isIntegerType() && SubTy->isIntegerType() &&
600          CGF) {
601        llvm::Value *Src = Visit(E->getSubExpr());
602        if (Src == 0) return 0;
603
604        // Use EmitScalarConversion to perform the conversion.
605        return cast<llvm::Constant>(CGF->EmitScalarConversion(Src, SubTy, Ty));
606      }
607
608      return 0;
609    }
610    }
611  }
612
613  llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
614    return Visit(DAE->getExpr());
615  }
616
617  llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
618    std::vector<llvm::Constant*> Elts;
619    const llvm::ArrayType *AType =
620        cast<llvm::ArrayType>(ConvertType(ILE->getType()));
621    unsigned NumInitElements = ILE->getNumInits();
622    // FIXME: Check for wide strings
623    // FIXME: Check for NumInitElements exactly equal to 1??
624    if (NumInitElements > 0 &&
625        (isa<StringLiteral>(ILE->getInit(0)) ||
626         isa<ObjCEncodeExpr>(ILE->getInit(0))) &&
627        ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
628      return Visit(ILE->getInit(0));
629    const llvm::Type *ElemTy = AType->getElementType();
630    unsigned NumElements = AType->getNumElements();
631
632    // Initialising an array requires us to automatically
633    // initialise any elements that have not been initialised explicitly
634    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
635
636    // Copy initializer elements.
637    unsigned i = 0;
638    bool RewriteType = false;
639    for (; i < NumInitableElts; ++i) {
640      Expr *Init = ILE->getInit(i);
641      llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
642      if (!C)
643        return 0;
644      RewriteType |= (C->getType() != ElemTy);
645      Elts.push_back(C);
646    }
647
648    // Initialize remaining array elements.
649    // FIXME: This doesn't handle member pointers correctly!
650    for (; i < NumElements; ++i)
651      Elts.push_back(llvm::Constant::getNullValue(ElemTy));
652
653    if (RewriteType) {
654      // FIXME: Try to avoid packing the array
655      std::vector<const llvm::Type*> Types;
656      for (unsigned i = 0; i < Elts.size(); ++i)
657        Types.push_back(Elts[i]->getType());
658      const llvm::StructType *SType = llvm::StructType::get(AType->getContext(),
659                                                            Types, true);
660      return llvm::ConstantStruct::get(SType, Elts);
661    }
662
663    return llvm::ConstantArray::get(AType, Elts);
664  }
665
666  llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
667    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
668  }
669
670  llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
671    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
672  }
673
674  llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
675    return CGM.EmitNullConstant(E->getType());
676  }
677
678  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
679    if (ILE->getType()->isScalarType()) {
680      // We have a scalar in braces. Just use the first element.
681      if (ILE->getNumInits() > 0) {
682        Expr *Init = ILE->getInit(0);
683        return CGM.EmitConstantExpr(Init, Init->getType(), CGF);
684      }
685      return CGM.EmitNullConstant(ILE->getType());
686    }
687
688    if (ILE->getType()->isArrayType())
689      return EmitArrayInitialization(ILE);
690
691    if (ILE->getType()->isRecordType())
692      return EmitStructInitialization(ILE);
693
694    if (ILE->getType()->isUnionType())
695      return EmitUnionInitialization(ILE);
696
697    // If ILE was a constant vector, we would have handled it already.
698    if (ILE->getType()->isVectorType())
699      return 0;
700
701    assert(0 && "Unable to handle InitListExpr");
702    // Get rid of control reaches end of void function warning.
703    // Not reached.
704    return 0;
705  }
706
707  llvm::Constant *VisitCXXConstructExpr(CXXConstructExpr *E) {
708    if (!E->getConstructor()->isTrivial())
709      return 0;
710
711    QualType Ty = E->getType();
712
713    // FIXME: We should not have to call getBaseElementType here.
714    const RecordType *RT =
715      CGM.getContext().getBaseElementType(Ty)->getAs<RecordType>();
716    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
717
718    // If the class doesn't have a trivial destructor, we can't emit it as a
719    // constant expr.
720    if (!RD->hasTrivialDestructor())
721      return 0;
722
723    // Only copy and default constructors can be trivial.
724
725
726    if (E->getNumArgs()) {
727      assert(E->getNumArgs() == 1 && "trivial ctor with > 1 argument");
728      assert(E->getConstructor()->isCopyConstructor() &&
729             "trivial ctor has argument but isn't a copy ctor");
730
731      Expr *Arg = E->getArg(0);
732      assert(CGM.getContext().hasSameUnqualifiedType(Ty, Arg->getType()) &&
733             "argument to copy ctor is of wrong type");
734
735      return Visit(Arg);
736    }
737
738    return CGM.EmitNullConstant(Ty);
739  }
740
741  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
742    assert(!E->getType()->isPointerType() && "Strings are always arrays");
743
744    // This must be a string initializing an array in a static initializer.
745    // Don't emit it as the address of the string, emit the string data itself
746    // as an inline array.
747    return llvm::ConstantArray::get(VMContext,
748                                    CGM.GetStringForStringLiteral(E), false);
749  }
750
751  llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
752    // This must be an @encode initializing an array in a static initializer.
753    // Don't emit it as the address of the string, emit the string data itself
754    // as an inline array.
755    std::string Str;
756    CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
757    const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
758
759    // Resize the string to the right size, adding zeros at the end, or
760    // truncating as needed.
761    Str.resize(CAT->getSize().getZExtValue(), '\0');
762    return llvm::ConstantArray::get(VMContext, Str, false);
763  }
764
765  llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
766    return Visit(E->getSubExpr());
767  }
768
769  // Utility methods
770  const llvm::Type *ConvertType(QualType T) {
771    return CGM.getTypes().ConvertType(T);
772  }
773
774public:
775  llvm::Constant *EmitLValue(Expr *E) {
776    switch (E->getStmtClass()) {
777    default: break;
778    case Expr::CompoundLiteralExprClass: {
779      // Note that due to the nature of compound literals, this is guaranteed
780      // to be the only use of the variable, so we just generate it here.
781      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
782      llvm::Constant* C = Visit(CLE->getInitializer());
783      // FIXME: "Leaked" on failure.
784      if (C)
785        C = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
786                                     E->getType().isConstant(CGM.getContext()),
787                                     llvm::GlobalValue::InternalLinkage,
788                                     C, ".compoundliteral", 0, false,
789                                     E->getType().getAddressSpace());
790      return C;
791    }
792    case Expr::DeclRefExprClass: {
793      ValueDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
794      if (Decl->hasAttr<WeakRefAttr>())
795	return CGM.GetWeakRefReference(Decl);
796      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
797        return CGM.GetAddrOfFunction(FD);
798      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
799        // We can never refer to a variable with local storage.
800        if (!VD->hasLocalStorage()) {
801          if (VD->isFileVarDecl() || VD->hasExternalStorage())
802            return CGM.GetAddrOfGlobalVar(VD);
803          else if (VD->isBlockVarDecl()) {
804            assert(CGF && "Can't access static local vars without CGF");
805            return CGF->GetAddrOfStaticLocalVar(VD);
806          }
807        }
808      }
809      break;
810    }
811    case Expr::StringLiteralClass:
812      return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
813    case Expr::ObjCEncodeExprClass:
814      return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
815    case Expr::ObjCStringLiteralClass: {
816      ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
817      llvm::Constant *C =
818          CGM.getObjCRuntime().GenerateConstantString(SL->getString());
819      return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
820    }
821    case Expr::PredefinedExprClass: {
822      unsigned Type = cast<PredefinedExpr>(E)->getIdentType();
823      if (CGF) {
824        LValue Res = CGF->EmitPredefinedFunctionName(Type);
825        return cast<llvm::Constant>(Res.getAddress());
826      } else if (Type == PredefinedExpr::PrettyFunction) {
827        return CGM.GetAddrOfConstantCString("top level", ".tmp");
828      }
829
830      return CGM.GetAddrOfConstantCString("", ".tmp");
831    }
832    case Expr::AddrLabelExprClass: {
833      assert(CGF && "Invalid address of label expression outside function.");
834      llvm::Constant *Ptr =
835        CGF->GetAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
836      return llvm::ConstantExpr::getBitCast(Ptr, ConvertType(E->getType()));
837    }
838    case Expr::CallExprClass: {
839      CallExpr* CE = cast<CallExpr>(E);
840      unsigned builtin = CE->isBuiltinCall(CGM.getContext());
841      if (builtin !=
842            Builtin::BI__builtin___CFStringMakeConstantString &&
843          builtin !=
844            Builtin::BI__builtin___NSStringMakeConstantString)
845        break;
846      const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
847      const StringLiteral *Literal = cast<StringLiteral>(Arg);
848      if (builtin ==
849            Builtin::BI__builtin___NSStringMakeConstantString) {
850        return CGM.getObjCRuntime().GenerateConstantString(Literal);
851      }
852      // FIXME: need to deal with UCN conversion issues.
853      return CGM.GetAddrOfConstantCFString(Literal);
854    }
855    case Expr::BlockExprClass: {
856      std::string FunctionName;
857      if (CGF)
858        FunctionName = CGF->CurFn->getName();
859      else
860        FunctionName = "global";
861
862      return CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
863    }
864    }
865
866    return 0;
867  }
868};
869
870}  // end anonymous namespace.
871
872llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
873                                                QualType DestType,
874                                                CodeGenFunction *CGF) {
875  Expr::EvalResult Result;
876
877  bool Success = false;
878
879  if (DestType->isReferenceType())
880    Success = E->EvaluateAsLValue(Result, Context);
881  else
882    Success = E->Evaluate(Result, Context);
883
884  if (Success && !Result.HasSideEffects) {
885    switch (Result.Val.getKind()) {
886    case APValue::Uninitialized:
887      assert(0 && "Constant expressions should be initialized.");
888      return 0;
889    case APValue::LValue: {
890      const llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
891      llvm::Constant *Offset =
892        llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext),
893                               Result.Val.getLValueOffset().getQuantity());
894
895      llvm::Constant *C;
896      if (const Expr *LVBase = Result.Val.getLValueBase()) {
897        C = ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
898
899        // Apply offset if necessary.
900        if (!Offset->isNullValue()) {
901          const llvm::Type *Type = llvm::Type::getInt8PtrTy(VMContext);
902          llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
903          Casted = llvm::ConstantExpr::getGetElementPtr(Casted, &Offset, 1);
904          C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
905        }
906
907        // Convert to the appropriate type; this could be an lvalue for
908        // an integer.
909        if (isa<llvm::PointerType>(DestTy))
910          return llvm::ConstantExpr::getBitCast(C, DestTy);
911
912        return llvm::ConstantExpr::getPtrToInt(C, DestTy);
913      } else {
914        C = Offset;
915
916        // Convert to the appropriate type; this could be an lvalue for
917        // an integer.
918        if (isa<llvm::PointerType>(DestTy))
919          return llvm::ConstantExpr::getIntToPtr(C, DestTy);
920
921        // If the types don't match this should only be a truncate.
922        if (C->getType() != DestTy)
923          return llvm::ConstantExpr::getTrunc(C, DestTy);
924
925        return C;
926      }
927    }
928    case APValue::Int: {
929      llvm::Constant *C = llvm::ConstantInt::get(VMContext,
930                                                 Result.Val.getInt());
931
932      if (C->getType() == llvm::Type::getInt1Ty(VMContext)) {
933        const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
934        C = llvm::ConstantExpr::getZExt(C, BoolTy);
935      }
936      return C;
937    }
938    case APValue::ComplexInt: {
939      llvm::Constant *Complex[2];
940
941      Complex[0] = llvm::ConstantInt::get(VMContext,
942                                          Result.Val.getComplexIntReal());
943      Complex[1] = llvm::ConstantInt::get(VMContext,
944                                          Result.Val.getComplexIntImag());
945
946      // FIXME: the target may want to specify that this is packed.
947      return llvm::ConstantStruct::get(VMContext, Complex, 2, false);
948    }
949    case APValue::Float:
950      return llvm::ConstantFP::get(VMContext, Result.Val.getFloat());
951    case APValue::ComplexFloat: {
952      llvm::Constant *Complex[2];
953
954      Complex[0] = llvm::ConstantFP::get(VMContext,
955                                         Result.Val.getComplexFloatReal());
956      Complex[1] = llvm::ConstantFP::get(VMContext,
957                                         Result.Val.getComplexFloatImag());
958
959      // FIXME: the target may want to specify that this is packed.
960      return llvm::ConstantStruct::get(VMContext, Complex, 2, false);
961    }
962    case APValue::Vector: {
963      llvm::SmallVector<llvm::Constant *, 4> Inits;
964      unsigned NumElts = Result.Val.getVectorLength();
965
966      for (unsigned i = 0; i != NumElts; ++i) {
967        APValue &Elt = Result.Val.getVectorElt(i);
968        if (Elt.isInt())
969          Inits.push_back(llvm::ConstantInt::get(VMContext, Elt.getInt()));
970        else
971          Inits.push_back(llvm::ConstantFP::get(VMContext, Elt.getFloat()));
972      }
973      return llvm::ConstantVector::get(&Inits[0], Inits.size());
974    }
975    }
976  }
977
978  llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
979  if (C && C->getType() == llvm::Type::getInt1Ty(VMContext)) {
980    const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
981    C = llvm::ConstantExpr::getZExt(C, BoolTy);
982  }
983  return C;
984}
985
986static bool containsPointerToDataMember(CodeGenTypes &Types, QualType T) {
987  // No need to check for member pointers when not compiling C++.
988  if (!Types.getContext().getLangOptions().CPlusPlus)
989    return false;
990
991  T = Types.getContext().getBaseElementType(T);
992
993  if (const RecordType *RT = T->getAs<RecordType>()) {
994    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
995
996    // FIXME: It would be better if there was a way to explicitly compute the
997    // record layout instead of converting to a type.
998    Types.ConvertTagDeclType(RD);
999
1000    const CGRecordLayout &Layout = Types.getCGRecordLayout(RD);
1001    return Layout.containsPointerToDataMember();
1002  }
1003
1004  if (const MemberPointerType *MPT = T->getAs<MemberPointerType>())
1005    return !MPT->getPointeeType()->isFunctionType();
1006
1007  return false;
1008}
1009
1010llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
1011  if (!containsPointerToDataMember(getTypes(), T))
1012    return llvm::Constant::getNullValue(getTypes().ConvertTypeForMem(T));
1013
1014  if (const ConstantArrayType *CAT = Context.getAsConstantArrayType(T)) {
1015
1016    QualType ElementTy = CAT->getElementType();
1017
1018    llvm::Constant *Element = EmitNullConstant(ElementTy);
1019    unsigned NumElements = CAT->getSize().getZExtValue();
1020    std::vector<llvm::Constant *> Array(NumElements);
1021    for (unsigned i = 0; i != NumElements; ++i)
1022      Array[i] = Element;
1023
1024    const llvm::ArrayType *ATy =
1025      cast<llvm::ArrayType>(getTypes().ConvertTypeForMem(T));
1026    return llvm::ConstantArray::get(ATy, Array);
1027  }
1028
1029  if (const RecordType *RT = T->getAs<RecordType>()) {
1030    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
1031    assert(!RD->getNumBases() &&
1032           "FIXME: Handle zero-initializing structs with bases and "
1033           "pointers to data members.");
1034    const llvm::StructType *STy =
1035      cast<llvm::StructType>(getTypes().ConvertTypeForMem(T));
1036    unsigned NumElements = STy->getNumElements();
1037    std::vector<llvm::Constant *> Elements(NumElements);
1038
1039    for (RecordDecl::field_iterator I = RD->field_begin(),
1040         E = RD->field_end(); I != E; ++I) {
1041      const FieldDecl *FD = *I;
1042
1043      const CGRecordLayout &RL =
1044        getTypes().getCGRecordLayout(FD->getParent());
1045      unsigned FieldNo = RL.getLLVMFieldNo(FD);
1046      Elements[FieldNo] = EmitNullConstant(FD->getType());
1047    }
1048
1049    // Now go through all other fields and zero them out.
1050    for (unsigned i = 0; i != NumElements; ++i) {
1051      if (!Elements[i])
1052        Elements[i] = llvm::Constant::getNullValue(STy->getElementType(i));
1053    }
1054
1055    return llvm::ConstantStruct::get(STy, Elements);
1056  }
1057
1058  assert(!T->getAs<MemberPointerType>()->getPointeeType()->isFunctionType() &&
1059         "Should only see pointers to data members here!");
1060
1061  // Itanium C++ ABI 2.3:
1062  //   A NULL pointer is represented as -1.
1063  return llvm::ConstantInt::get(getTypes().ConvertTypeForMem(T), -1ULL,
1064                                /*isSigned=*/true);
1065}
1066
1067llvm::Constant *
1068CodeGenModule::EmitPointerToDataMember(const FieldDecl *FD) {
1069
1070  // Itanium C++ ABI 2.3:
1071  //   A pointer to data member is an offset from the base address of the class
1072  //   object containing it, represented as a ptrdiff_t
1073
1074  const CXXRecordDecl *ClassDecl = cast<CXXRecordDecl>(FD->getParent());
1075  QualType ClassType =
1076    getContext().getTypeDeclType(const_cast<CXXRecordDecl *>(ClassDecl));
1077
1078  const llvm::StructType *ClassLTy =
1079    cast<llvm::StructType>(getTypes().ConvertType(ClassType));
1080
1081  const CGRecordLayout &RL =
1082    getTypes().getCGRecordLayout(FD->getParent());
1083  unsigned FieldNo = RL.getLLVMFieldNo(FD);
1084  uint64_t Offset =
1085    getTargetData().getStructLayout(ClassLTy)->getElementOffset(FieldNo);
1086
1087  const llvm::Type *PtrDiffTy =
1088    getTypes().ConvertType(getContext().getPointerDiffType());
1089
1090  return llvm::ConstantInt::get(PtrDiffTy, Offset);
1091}
1092