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 "CGCXXABI.h"
16#include "CGObjCRuntime.h"
17#include "CGRecordLayout.h"
18#include "CodeGenModule.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/IR/Constants.h"
25#include "llvm/IR/DataLayout.h"
26#include "llvm/IR/Function.h"
27#include "llvm/IR/GlobalVariable.h"
28using namespace clang;
29using namespace CodeGen;
30
31//===----------------------------------------------------------------------===//
32//                            ConstStructBuilder
33//===----------------------------------------------------------------------===//
34
35namespace {
36class ConstExprEmitter;
37class ConstStructBuilder {
38  CodeGenModule &CGM;
39  CodeGenFunction *CGF;
40
41  bool Packed;
42  CharUnits NextFieldOffsetInChars;
43  CharUnits LLVMStructAlignment;
44  SmallVector<llvm::Constant *, 32> Elements;
45public:
46  static llvm::Constant *BuildStruct(CodeGenModule &CGM, CodeGenFunction *CFG,
47                                     ConstExprEmitter *Emitter,
48                                     llvm::ConstantStruct *Base,
49                                     InitListExpr *Updater);
50  static llvm::Constant *BuildStruct(CodeGenModule &CGM, CodeGenFunction *CGF,
51                                     InitListExpr *ILE);
52  static llvm::Constant *BuildStruct(CodeGenModule &CGM, CodeGenFunction *CGF,
53                                     const APValue &Value, QualType ValTy);
54
55private:
56  ConstStructBuilder(CodeGenModule &CGM, CodeGenFunction *CGF)
57    : CGM(CGM), CGF(CGF), Packed(false),
58    NextFieldOffsetInChars(CharUnits::Zero()),
59    LLVMStructAlignment(CharUnits::One()) { }
60
61  void AppendField(const FieldDecl *Field, uint64_t FieldOffset,
62                   llvm::Constant *InitExpr);
63
64  void AppendBytes(CharUnits FieldOffsetInChars, llvm::Constant *InitCst);
65
66  void AppendBitField(const FieldDecl *Field, uint64_t FieldOffset,
67                      llvm::ConstantInt *InitExpr);
68
69  void AppendPadding(CharUnits PadSize);
70
71  void AppendTailPadding(CharUnits RecordSize);
72
73  void ConvertStructToPacked();
74
75  bool Build(InitListExpr *ILE);
76  bool Build(ConstExprEmitter *Emitter, llvm::ConstantStruct *Base,
77             InitListExpr *Updater);
78  void Build(const APValue &Val, const RecordDecl *RD, bool IsPrimaryBase,
79             const CXXRecordDecl *VTableClass, CharUnits BaseOffset);
80  llvm::Constant *Finalize(QualType Ty);
81
82  CharUnits getAlignment(const llvm::Constant *C) const {
83    if (Packed)  return CharUnits::One();
84    return CharUnits::fromQuantity(
85        CGM.getDataLayout().getABITypeAlignment(C->getType()));
86  }
87
88  CharUnits getSizeInChars(const llvm::Constant *C) const {
89    return CharUnits::fromQuantity(
90        CGM.getDataLayout().getTypeAllocSize(C->getType()));
91  }
92};
93
94void ConstStructBuilder::
95AppendField(const FieldDecl *Field, uint64_t FieldOffset,
96            llvm::Constant *InitCst) {
97  const ASTContext &Context = CGM.getContext();
98
99  CharUnits FieldOffsetInChars = Context.toCharUnitsFromBits(FieldOffset);
100
101  AppendBytes(FieldOffsetInChars, InitCst);
102}
103
104void ConstStructBuilder::
105AppendBytes(CharUnits FieldOffsetInChars, llvm::Constant *InitCst) {
106
107  assert(NextFieldOffsetInChars <= FieldOffsetInChars
108         && "Field offset mismatch!");
109
110  CharUnits FieldAlignment = getAlignment(InitCst);
111
112  // Round up the field offset to the alignment of the field type.
113  CharUnits AlignedNextFieldOffsetInChars =
114      NextFieldOffsetInChars.alignTo(FieldAlignment);
115
116  if (AlignedNextFieldOffsetInChars < FieldOffsetInChars) {
117    // We need to append padding.
118    AppendPadding(FieldOffsetInChars - NextFieldOffsetInChars);
119
120    assert(NextFieldOffsetInChars == FieldOffsetInChars &&
121           "Did not add enough padding!");
122
123    AlignedNextFieldOffsetInChars =
124        NextFieldOffsetInChars.alignTo(FieldAlignment);
125  }
126
127  if (AlignedNextFieldOffsetInChars > FieldOffsetInChars) {
128    assert(!Packed && "Alignment is wrong even with a packed struct!");
129
130    // Convert the struct to a packed struct.
131    ConvertStructToPacked();
132
133    // After we pack the struct, we may need to insert padding.
134    if (NextFieldOffsetInChars < FieldOffsetInChars) {
135      // We need to append padding.
136      AppendPadding(FieldOffsetInChars - NextFieldOffsetInChars);
137
138      assert(NextFieldOffsetInChars == FieldOffsetInChars &&
139             "Did not add enough padding!");
140    }
141    AlignedNextFieldOffsetInChars = NextFieldOffsetInChars;
142  }
143
144  // Add the field.
145  Elements.push_back(InitCst);
146  NextFieldOffsetInChars = AlignedNextFieldOffsetInChars +
147                           getSizeInChars(InitCst);
148
149  if (Packed)
150    assert(LLVMStructAlignment == CharUnits::One() &&
151           "Packed struct not byte-aligned!");
152  else
153    LLVMStructAlignment = std::max(LLVMStructAlignment, FieldAlignment);
154}
155
156void ConstStructBuilder::AppendBitField(const FieldDecl *Field,
157                                        uint64_t FieldOffset,
158                                        llvm::ConstantInt *CI) {
159  const ASTContext &Context = CGM.getContext();
160  const uint64_t CharWidth = Context.getCharWidth();
161  uint64_t NextFieldOffsetInBits = Context.toBits(NextFieldOffsetInChars);
162  if (FieldOffset > NextFieldOffsetInBits) {
163    // We need to add padding.
164    CharUnits PadSize = Context.toCharUnitsFromBits(
165        llvm::alignTo(FieldOffset - NextFieldOffsetInBits,
166                      Context.getTargetInfo().getCharAlign()));
167
168    AppendPadding(PadSize);
169  }
170
171  uint64_t FieldSize = Field->getBitWidthValue(Context);
172
173  llvm::APInt FieldValue = CI->getValue();
174
175  // Promote the size of FieldValue if necessary
176  // FIXME: This should never occur, but currently it can because initializer
177  // constants are cast to bool, and because clang is not enforcing bitfield
178  // width limits.
179  if (FieldSize > FieldValue.getBitWidth())
180    FieldValue = FieldValue.zext(FieldSize);
181
182  // Truncate the size of FieldValue to the bit field size.
183  if (FieldSize < FieldValue.getBitWidth())
184    FieldValue = FieldValue.trunc(FieldSize);
185
186  NextFieldOffsetInBits = Context.toBits(NextFieldOffsetInChars);
187  if (FieldOffset < NextFieldOffsetInBits) {
188    // Either part of the field or the entire field can go into the previous
189    // byte.
190    assert(!Elements.empty() && "Elements can't be empty!");
191
192    unsigned BitsInPreviousByte = NextFieldOffsetInBits - FieldOffset;
193
194    bool FitsCompletelyInPreviousByte =
195      BitsInPreviousByte >= FieldValue.getBitWidth();
196
197    llvm::APInt Tmp = FieldValue;
198
199    if (!FitsCompletelyInPreviousByte) {
200      unsigned NewFieldWidth = FieldSize - BitsInPreviousByte;
201
202      if (CGM.getDataLayout().isBigEndian()) {
203        Tmp = Tmp.lshr(NewFieldWidth);
204        Tmp = Tmp.trunc(BitsInPreviousByte);
205
206        // We want the remaining high bits.
207        FieldValue = FieldValue.trunc(NewFieldWidth);
208      } else {
209        Tmp = Tmp.trunc(BitsInPreviousByte);
210
211        // We want the remaining low bits.
212        FieldValue = FieldValue.lshr(BitsInPreviousByte);
213        FieldValue = FieldValue.trunc(NewFieldWidth);
214      }
215    }
216
217    Tmp = Tmp.zext(CharWidth);
218    if (CGM.getDataLayout().isBigEndian()) {
219      if (FitsCompletelyInPreviousByte)
220        Tmp = Tmp.shl(BitsInPreviousByte - FieldValue.getBitWidth());
221    } else {
222      Tmp = Tmp.shl(CharWidth - BitsInPreviousByte);
223    }
224
225    // 'or' in the bits that go into the previous byte.
226    llvm::Value *LastElt = Elements.back();
227    if (llvm::ConstantInt *Val = dyn_cast<llvm::ConstantInt>(LastElt))
228      Tmp |= Val->getValue();
229    else {
230      assert(isa<llvm::UndefValue>(LastElt));
231      // If there is an undef field that we're adding to, it can either be a
232      // scalar undef (in which case, we just replace it with our field) or it
233      // is an array.  If it is an array, we have to pull one byte off the
234      // array so that the other undef bytes stay around.
235      if (!isa<llvm::IntegerType>(LastElt->getType())) {
236        // The undef padding will be a multibyte array, create a new smaller
237        // padding and then an hole for our i8 to get plopped into.
238        assert(isa<llvm::ArrayType>(LastElt->getType()) &&
239               "Expected array padding of undefs");
240        llvm::ArrayType *AT = cast<llvm::ArrayType>(LastElt->getType());
241        assert(AT->getElementType()->isIntegerTy(CharWidth) &&
242               AT->getNumElements() != 0 &&
243               "Expected non-empty array padding of undefs");
244
245        // Remove the padding array.
246        NextFieldOffsetInChars -= CharUnits::fromQuantity(AT->getNumElements());
247        Elements.pop_back();
248
249        // Add the padding back in two chunks.
250        AppendPadding(CharUnits::fromQuantity(AT->getNumElements()-1));
251        AppendPadding(CharUnits::One());
252        assert(isa<llvm::UndefValue>(Elements.back()) &&
253               Elements.back()->getType()->isIntegerTy(CharWidth) &&
254               "Padding addition didn't work right");
255      }
256    }
257
258    Elements.back() = llvm::ConstantInt::get(CGM.getLLVMContext(), Tmp);
259
260    if (FitsCompletelyInPreviousByte)
261      return;
262  }
263
264  while (FieldValue.getBitWidth() > CharWidth) {
265    llvm::APInt Tmp;
266
267    if (CGM.getDataLayout().isBigEndian()) {
268      // We want the high bits.
269      Tmp =
270        FieldValue.lshr(FieldValue.getBitWidth() - CharWidth).trunc(CharWidth);
271    } else {
272      // We want the low bits.
273      Tmp = FieldValue.trunc(CharWidth);
274
275      FieldValue = FieldValue.lshr(CharWidth);
276    }
277
278    Elements.push_back(llvm::ConstantInt::get(CGM.getLLVMContext(), Tmp));
279    ++NextFieldOffsetInChars;
280
281    FieldValue = FieldValue.trunc(FieldValue.getBitWidth() - CharWidth);
282  }
283
284  assert(FieldValue.getBitWidth() > 0 &&
285         "Should have at least one bit left!");
286  assert(FieldValue.getBitWidth() <= CharWidth &&
287         "Should not have more than a byte left!");
288
289  if (FieldValue.getBitWidth() < CharWidth) {
290    if (CGM.getDataLayout().isBigEndian()) {
291      unsigned BitWidth = FieldValue.getBitWidth();
292
293      FieldValue = FieldValue.zext(CharWidth) << (CharWidth - BitWidth);
294    } else
295      FieldValue = FieldValue.zext(CharWidth);
296  }
297
298  // Append the last element.
299  Elements.push_back(llvm::ConstantInt::get(CGM.getLLVMContext(),
300                                            FieldValue));
301  ++NextFieldOffsetInChars;
302}
303
304void ConstStructBuilder::AppendPadding(CharUnits PadSize) {
305  if (PadSize.isZero())
306    return;
307
308  llvm::Type *Ty = CGM.Int8Ty;
309  if (PadSize > CharUnits::One())
310    Ty = llvm::ArrayType::get(Ty, PadSize.getQuantity());
311
312  llvm::Constant *C = llvm::UndefValue::get(Ty);
313  Elements.push_back(C);
314  assert(getAlignment(C) == CharUnits::One() &&
315         "Padding must have 1 byte alignment!");
316
317  NextFieldOffsetInChars += getSizeInChars(C);
318}
319
320void ConstStructBuilder::AppendTailPadding(CharUnits RecordSize) {
321  assert(NextFieldOffsetInChars <= RecordSize &&
322         "Size mismatch!");
323
324  AppendPadding(RecordSize - NextFieldOffsetInChars);
325}
326
327void ConstStructBuilder::ConvertStructToPacked() {
328  SmallVector<llvm::Constant *, 16> PackedElements;
329  CharUnits ElementOffsetInChars = CharUnits::Zero();
330
331  for (unsigned i = 0, e = Elements.size(); i != e; ++i) {
332    llvm::Constant *C = Elements[i];
333
334    CharUnits ElementAlign = CharUnits::fromQuantity(
335      CGM.getDataLayout().getABITypeAlignment(C->getType()));
336    CharUnits AlignedElementOffsetInChars =
337        ElementOffsetInChars.alignTo(ElementAlign);
338
339    if (AlignedElementOffsetInChars > ElementOffsetInChars) {
340      // We need some padding.
341      CharUnits NumChars =
342        AlignedElementOffsetInChars - ElementOffsetInChars;
343
344      llvm::Type *Ty = CGM.Int8Ty;
345      if (NumChars > CharUnits::One())
346        Ty = llvm::ArrayType::get(Ty, NumChars.getQuantity());
347
348      llvm::Constant *Padding = llvm::UndefValue::get(Ty);
349      PackedElements.push_back(Padding);
350      ElementOffsetInChars += getSizeInChars(Padding);
351    }
352
353    PackedElements.push_back(C);
354    ElementOffsetInChars += getSizeInChars(C);
355  }
356
357  assert(ElementOffsetInChars == NextFieldOffsetInChars &&
358         "Packing the struct changed its size!");
359
360  Elements.swap(PackedElements);
361  LLVMStructAlignment = CharUnits::One();
362  Packed = true;
363}
364
365bool ConstStructBuilder::Build(InitListExpr *ILE) {
366  RecordDecl *RD = ILE->getType()->getAs<RecordType>()->getDecl();
367  const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
368
369  unsigned FieldNo = 0;
370  unsigned ElementNo = 0;
371
372  // Bail out if we have base classes. We could support these, but they only
373  // arise in C++1z where we will have already constant folded most interesting
374  // cases. FIXME: There are still a few more cases we can handle this way.
375  if (auto *CXXRD = dyn_cast<CXXRecordDecl>(RD))
376    if (CXXRD->getNumBases())
377      return false;
378
379  for (RecordDecl::field_iterator Field = RD->field_begin(),
380       FieldEnd = RD->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
381    // If this is a union, skip all the fields that aren't being initialized.
382    if (RD->isUnion() && ILE->getInitializedFieldInUnion() != *Field)
383      continue;
384
385    // Don't emit anonymous bitfields, they just affect layout.
386    if (Field->isUnnamedBitfield())
387      continue;
388
389    // Get the initializer.  A struct can include fields without initializers,
390    // we just use explicit null values for them.
391    llvm::Constant *EltInit;
392    if (ElementNo < ILE->getNumInits())
393      EltInit = CGM.EmitConstantExpr(ILE->getInit(ElementNo++),
394                                     Field->getType(), CGF);
395    else
396      EltInit = CGM.EmitNullConstant(Field->getType());
397
398    if (!EltInit)
399      return false;
400
401    if (!Field->isBitField()) {
402      // Handle non-bitfield members.
403      AppendField(*Field, Layout.getFieldOffset(FieldNo), EltInit);
404    } else {
405      // Otherwise we have a bitfield.
406      if (auto *CI = dyn_cast<llvm::ConstantInt>(EltInit)) {
407        AppendBitField(*Field, Layout.getFieldOffset(FieldNo), CI);
408      } else {
409        // We are trying to initialize a bitfield with a non-trivial constant,
410        // this must require run-time code.
411        return false;
412      }
413    }
414  }
415
416  return true;
417}
418
419namespace {
420struct BaseInfo {
421  BaseInfo(const CXXRecordDecl *Decl, CharUnits Offset, unsigned Index)
422    : Decl(Decl), Offset(Offset), Index(Index) {
423  }
424
425  const CXXRecordDecl *Decl;
426  CharUnits Offset;
427  unsigned Index;
428
429  bool operator<(const BaseInfo &O) const { return Offset < O.Offset; }
430};
431}
432
433void ConstStructBuilder::Build(const APValue &Val, const RecordDecl *RD,
434                               bool IsPrimaryBase,
435                               const CXXRecordDecl *VTableClass,
436                               CharUnits Offset) {
437  const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
438
439  if (const CXXRecordDecl *CD = dyn_cast<CXXRecordDecl>(RD)) {
440    // Add a vtable pointer, if we need one and it hasn't already been added.
441    if (CD->isDynamicClass() && !IsPrimaryBase) {
442      llvm::Constant *VTableAddressPoint =
443          CGM.getCXXABI().getVTableAddressPointForConstExpr(
444              BaseSubobject(CD, Offset), VTableClass);
445      AppendBytes(Offset, VTableAddressPoint);
446    }
447
448    // Accumulate and sort bases, in order to visit them in address order, which
449    // may not be the same as declaration order.
450    SmallVector<BaseInfo, 8> Bases;
451    Bases.reserve(CD->getNumBases());
452    unsigned BaseNo = 0;
453    for (CXXRecordDecl::base_class_const_iterator Base = CD->bases_begin(),
454         BaseEnd = CD->bases_end(); Base != BaseEnd; ++Base, ++BaseNo) {
455      assert(!Base->isVirtual() && "should not have virtual bases here");
456      const CXXRecordDecl *BD = Base->getType()->getAsCXXRecordDecl();
457      CharUnits BaseOffset = Layout.getBaseClassOffset(BD);
458      Bases.push_back(BaseInfo(BD, BaseOffset, BaseNo));
459    }
460    std::stable_sort(Bases.begin(), Bases.end());
461
462    for (unsigned I = 0, N = Bases.size(); I != N; ++I) {
463      BaseInfo &Base = Bases[I];
464
465      bool IsPrimaryBase = Layout.getPrimaryBase() == Base.Decl;
466      Build(Val.getStructBase(Base.Index), Base.Decl, IsPrimaryBase,
467            VTableClass, Offset + Base.Offset);
468    }
469  }
470
471  unsigned FieldNo = 0;
472  uint64_t OffsetBits = CGM.getContext().toBits(Offset);
473
474  for (RecordDecl::field_iterator Field = RD->field_begin(),
475       FieldEnd = RD->field_end(); Field != FieldEnd; ++Field, ++FieldNo) {
476    // If this is a union, skip all the fields that aren't being initialized.
477    if (RD->isUnion() && Val.getUnionField() != *Field)
478      continue;
479
480    // Don't emit anonymous bitfields, they just affect layout.
481    if (Field->isUnnamedBitfield())
482      continue;
483
484    // Emit the value of the initializer.
485    const APValue &FieldValue =
486      RD->isUnion() ? Val.getUnionValue() : Val.getStructField(FieldNo);
487    llvm::Constant *EltInit =
488      CGM.EmitConstantValueForMemory(FieldValue, Field->getType(), CGF);
489    assert(EltInit && "EmitConstantValue can't fail");
490
491    if (!Field->isBitField()) {
492      // Handle non-bitfield members.
493      AppendField(*Field, Layout.getFieldOffset(FieldNo) + OffsetBits, EltInit);
494    } else {
495      // Otherwise we have a bitfield.
496      AppendBitField(*Field, Layout.getFieldOffset(FieldNo) + OffsetBits,
497                     cast<llvm::ConstantInt>(EltInit));
498    }
499  }
500}
501
502llvm::Constant *ConstStructBuilder::Finalize(QualType Ty) {
503  RecordDecl *RD = Ty->getAs<RecordType>()->getDecl();
504  const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
505
506  CharUnits LayoutSizeInChars = Layout.getSize();
507
508  if (NextFieldOffsetInChars > LayoutSizeInChars) {
509    // If the struct is bigger than the size of the record type,
510    // we must have a flexible array member at the end.
511    assert(RD->hasFlexibleArrayMember() &&
512           "Must have flexible array member if struct is bigger than type!");
513
514    // No tail padding is necessary.
515  } else {
516    // Append tail padding if necessary.
517    CharUnits LLVMSizeInChars =
518        NextFieldOffsetInChars.alignTo(LLVMStructAlignment);
519
520    if (LLVMSizeInChars != LayoutSizeInChars)
521      AppendTailPadding(LayoutSizeInChars);
522
523    LLVMSizeInChars = NextFieldOffsetInChars.alignTo(LLVMStructAlignment);
524
525    // Check if we need to convert the struct to a packed struct.
526    if (NextFieldOffsetInChars <= LayoutSizeInChars &&
527        LLVMSizeInChars > LayoutSizeInChars) {
528      assert(!Packed && "Size mismatch!");
529
530      ConvertStructToPacked();
531      assert(NextFieldOffsetInChars <= LayoutSizeInChars &&
532             "Converting to packed did not help!");
533    }
534
535    LLVMSizeInChars = NextFieldOffsetInChars.alignTo(LLVMStructAlignment);
536
537    assert(LayoutSizeInChars == LLVMSizeInChars &&
538           "Tail padding mismatch!");
539  }
540
541  // Pick the type to use.  If the type is layout identical to the ConvertType
542  // type then use it, otherwise use whatever the builder produced for us.
543  llvm::StructType *STy =
544      llvm::ConstantStruct::getTypeForElements(CGM.getLLVMContext(),
545                                               Elements, Packed);
546  llvm::Type *ValTy = CGM.getTypes().ConvertType(Ty);
547  if (llvm::StructType *ValSTy = dyn_cast<llvm::StructType>(ValTy)) {
548    if (ValSTy->isLayoutIdentical(STy))
549      STy = ValSTy;
550  }
551
552  llvm::Constant *Result = llvm::ConstantStruct::get(STy, Elements);
553
554  assert(NextFieldOffsetInChars.alignTo(getAlignment(Result)) ==
555             getSizeInChars(Result) &&
556         "Size mismatch!");
557
558  return Result;
559}
560
561llvm::Constant *ConstStructBuilder::BuildStruct(CodeGenModule &CGM,
562                                                CodeGenFunction *CGF,
563                                                ConstExprEmitter *Emitter,
564                                                llvm::ConstantStruct *Base,
565                                                InitListExpr *Updater) {
566  ConstStructBuilder Builder(CGM, CGF);
567  if (!Builder.Build(Emitter, Base, Updater))
568    return nullptr;
569  return Builder.Finalize(Updater->getType());
570}
571
572llvm::Constant *ConstStructBuilder::BuildStruct(CodeGenModule &CGM,
573                                                CodeGenFunction *CGF,
574                                                InitListExpr *ILE) {
575  ConstStructBuilder Builder(CGM, CGF);
576
577  if (!Builder.Build(ILE))
578    return nullptr;
579
580  return Builder.Finalize(ILE->getType());
581}
582
583llvm::Constant *ConstStructBuilder::BuildStruct(CodeGenModule &CGM,
584                                                CodeGenFunction *CGF,
585                                                const APValue &Val,
586                                                QualType ValTy) {
587  ConstStructBuilder Builder(CGM, CGF);
588
589  const RecordDecl *RD = ValTy->castAs<RecordType>()->getDecl();
590  const CXXRecordDecl *CD = dyn_cast<CXXRecordDecl>(RD);
591  Builder.Build(Val, RD, false, CD, CharUnits::Zero());
592
593  return Builder.Finalize(ValTy);
594}
595
596
597//===----------------------------------------------------------------------===//
598//                             ConstExprEmitter
599//===----------------------------------------------------------------------===//
600
601/// This class only needs to handle two cases:
602/// 1) Literals (this is used by APValue emission to emit literals).
603/// 2) Arrays, structs and unions (outside C++11 mode, we don't currently
604///    constant fold these types).
605class ConstExprEmitter :
606  public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
607  CodeGenModule &CGM;
608  CodeGenFunction *CGF;
609  llvm::LLVMContext &VMContext;
610public:
611  ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
612    : CGM(cgm), CGF(cgf), VMContext(cgm.getLLVMContext()) {
613  }
614
615  //===--------------------------------------------------------------------===//
616  //                            Visitor Methods
617  //===--------------------------------------------------------------------===//
618
619  llvm::Constant *VisitStmt(Stmt *S) {
620    return nullptr;
621  }
622
623  llvm::Constant *VisitParenExpr(ParenExpr *PE) {
624    return Visit(PE->getSubExpr());
625  }
626
627  llvm::Constant *
628  VisitSubstNonTypeTemplateParmExpr(SubstNonTypeTemplateParmExpr *PE) {
629    return Visit(PE->getReplacement());
630  }
631
632  llvm::Constant *VisitGenericSelectionExpr(GenericSelectionExpr *GE) {
633    return Visit(GE->getResultExpr());
634  }
635
636  llvm::Constant *VisitChooseExpr(ChooseExpr *CE) {
637    return Visit(CE->getChosenSubExpr());
638  }
639
640  llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
641    return Visit(E->getInitializer());
642  }
643
644  llvm::Constant *VisitCastExpr(CastExpr* E) {
645    if (const auto *ECE = dyn_cast<ExplicitCastExpr>(E))
646      CGM.EmitExplicitCastExprType(ECE, CGF);
647    Expr *subExpr = E->getSubExpr();
648    llvm::Constant *C = CGM.EmitConstantExpr(subExpr, subExpr->getType(), CGF);
649    if (!C) return nullptr;
650
651    llvm::Type *destType = ConvertType(E->getType());
652
653    switch (E->getCastKind()) {
654    case CK_ToUnion: {
655      // GCC cast to union extension
656      assert(E->getType()->isUnionType() &&
657             "Destination type is not union type!");
658
659      // Build a struct with the union sub-element as the first member,
660      // and padded to the appropriate size
661      SmallVector<llvm::Constant*, 2> Elts;
662      SmallVector<llvm::Type*, 2> Types;
663      Elts.push_back(C);
664      Types.push_back(C->getType());
665      unsigned CurSize = CGM.getDataLayout().getTypeAllocSize(C->getType());
666      unsigned TotalSize = CGM.getDataLayout().getTypeAllocSize(destType);
667
668      assert(CurSize <= TotalSize && "Union size mismatch!");
669      if (unsigned NumPadBytes = TotalSize - CurSize) {
670        llvm::Type *Ty = CGM.Int8Ty;
671        if (NumPadBytes > 1)
672          Ty = llvm::ArrayType::get(Ty, NumPadBytes);
673
674        Elts.push_back(llvm::UndefValue::get(Ty));
675        Types.push_back(Ty);
676      }
677
678      llvm::StructType* STy =
679        llvm::StructType::get(C->getType()->getContext(), Types, false);
680      return llvm::ConstantStruct::get(STy, Elts);
681    }
682
683    case CK_AddressSpaceConversion:
684      return llvm::ConstantExpr::getAddrSpaceCast(C, destType);
685
686    case CK_LValueToRValue:
687    case CK_AtomicToNonAtomic:
688    case CK_NonAtomicToAtomic:
689    case CK_NoOp:
690    case CK_ConstructorConversion:
691      return C;
692
693    case CK_Dependent: llvm_unreachable("saw dependent cast!");
694
695    case CK_BuiltinFnToFnPtr:
696      llvm_unreachable("builtin functions are handled elsewhere");
697
698    case CK_ReinterpretMemberPointer:
699    case CK_DerivedToBaseMemberPointer:
700    case CK_BaseToDerivedMemberPointer:
701      return CGM.getCXXABI().EmitMemberPointerConversion(E, C);
702
703    // These will never be supported.
704    case CK_ObjCObjectLValueCast:
705    case CK_ARCProduceObject:
706    case CK_ARCConsumeObject:
707    case CK_ARCReclaimReturnedObject:
708    case CK_ARCExtendBlockObject:
709    case CK_CopyAndAutoreleaseBlockObject:
710      return nullptr;
711
712    // These don't need to be handled here because Evaluate knows how to
713    // evaluate them in the cases where they can be folded.
714    case CK_BitCast:
715    case CK_ToVoid:
716    case CK_Dynamic:
717    case CK_LValueBitCast:
718    case CK_NullToMemberPointer:
719    case CK_UserDefinedConversion:
720    case CK_CPointerToObjCPointerCast:
721    case CK_BlockPointerToObjCPointerCast:
722    case CK_AnyPointerToBlockPointerCast:
723    case CK_ArrayToPointerDecay:
724    case CK_FunctionToPointerDecay:
725    case CK_BaseToDerived:
726    case CK_DerivedToBase:
727    case CK_UncheckedDerivedToBase:
728    case CK_MemberPointerToBoolean:
729    case CK_VectorSplat:
730    case CK_FloatingRealToComplex:
731    case CK_FloatingComplexToReal:
732    case CK_FloatingComplexToBoolean:
733    case CK_FloatingComplexCast:
734    case CK_FloatingComplexToIntegralComplex:
735    case CK_IntegralRealToComplex:
736    case CK_IntegralComplexToReal:
737    case CK_IntegralComplexToBoolean:
738    case CK_IntegralComplexCast:
739    case CK_IntegralComplexToFloatingComplex:
740    case CK_PointerToIntegral:
741    case CK_PointerToBoolean:
742    case CK_NullToPointer:
743    case CK_IntegralCast:
744    case CK_BooleanToSignedIntegral:
745    case CK_IntegralToPointer:
746    case CK_IntegralToBoolean:
747    case CK_IntegralToFloating:
748    case CK_FloatingToIntegral:
749    case CK_FloatingToBoolean:
750    case CK_FloatingCast:
751    case CK_ZeroToOCLEvent:
752      return nullptr;
753    }
754    llvm_unreachable("Invalid CastKind");
755  }
756
757  llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
758    return Visit(DAE->getExpr());
759  }
760
761  llvm::Constant *VisitCXXDefaultInitExpr(CXXDefaultInitExpr *DIE) {
762    // No need for a DefaultInitExprScope: we don't handle 'this' in a
763    // constant expression.
764    return Visit(DIE->getExpr());
765  }
766
767  llvm::Constant *VisitExprWithCleanups(ExprWithCleanups *E) {
768    if (!E->cleanupsHaveSideEffects())
769      return Visit(E->getSubExpr());
770    return nullptr;
771  }
772
773  llvm::Constant *VisitMaterializeTemporaryExpr(MaterializeTemporaryExpr *E) {
774    return Visit(E->GetTemporaryExpr());
775  }
776
777  llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
778    if (ILE->isStringLiteralInit())
779      return Visit(ILE->getInit(0));
780
781    llvm::ArrayType *AType =
782        cast<llvm::ArrayType>(ConvertType(ILE->getType()));
783    llvm::Type *ElemTy = AType->getElementType();
784    unsigned NumInitElements = ILE->getNumInits();
785    unsigned NumElements = AType->getNumElements();
786
787    // Initialising an array requires us to automatically
788    // initialise any elements that have not been initialised explicitly
789    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
790
791    // Initialize remaining array elements.
792    // FIXME: This doesn't handle member pointers correctly!
793    llvm::Constant *fillC;
794    if (Expr *filler = ILE->getArrayFiller())
795      fillC = CGM.EmitConstantExpr(filler, filler->getType(), CGF);
796    else
797      fillC = llvm::Constant::getNullValue(ElemTy);
798    if (!fillC)
799      return nullptr;
800
801    // Try to use a ConstantAggregateZero if we can.
802    if (fillC->isNullValue() && !NumInitableElts)
803      return llvm::ConstantAggregateZero::get(AType);
804
805    // Copy initializer elements.
806    std::vector<llvm::Constant*> Elts;
807    Elts.reserve(NumInitableElts + NumElements);
808
809    bool RewriteType = false;
810    for (unsigned i = 0; i < NumInitableElts; ++i) {
811      Expr *Init = ILE->getInit(i);
812      llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
813      if (!C)
814        return nullptr;
815      RewriteType |= (C->getType() != ElemTy);
816      Elts.push_back(C);
817    }
818
819    RewriteType |= (fillC->getType() != ElemTy);
820    Elts.resize(NumElements, fillC);
821
822    if (RewriteType) {
823      // FIXME: Try to avoid packing the array
824      std::vector<llvm::Type*> Types;
825      Types.reserve(NumInitableElts + NumElements);
826      for (unsigned i = 0, e = Elts.size(); i < e; ++i)
827        Types.push_back(Elts[i]->getType());
828      llvm::StructType *SType = llvm::StructType::get(AType->getContext(),
829                                                            Types, true);
830      return llvm::ConstantStruct::get(SType, Elts);
831    }
832
833    return llvm::ConstantArray::get(AType, Elts);
834  }
835
836  llvm::Constant *EmitRecordInitialization(InitListExpr *ILE) {
837    return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
838  }
839
840  llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
841    return CGM.EmitNullConstant(E->getType());
842  }
843
844  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
845    if (ILE->getType()->isArrayType())
846      return EmitArrayInitialization(ILE);
847
848    if (ILE->getType()->isRecordType())
849      return EmitRecordInitialization(ILE);
850
851    return nullptr;
852  }
853
854  llvm::Constant *EmitDesignatedInitUpdater(llvm::Constant *Base,
855                                            InitListExpr *Updater) {
856    QualType ExprType = Updater->getType();
857
858    if (ExprType->isArrayType()) {
859      llvm::ArrayType *AType = cast<llvm::ArrayType>(ConvertType(ExprType));
860      llvm::Type *ElemType = AType->getElementType();
861
862      unsigned NumInitElements = Updater->getNumInits();
863      unsigned NumElements = AType->getNumElements();
864
865      std::vector<llvm::Constant *> Elts;
866      Elts.reserve(NumElements);
867
868      if (llvm::ConstantDataArray *DataArray =
869            dyn_cast<llvm::ConstantDataArray>(Base))
870        for (unsigned i = 0; i != NumElements; ++i)
871          Elts.push_back(DataArray->getElementAsConstant(i));
872      else if (llvm::ConstantArray *Array =
873                 dyn_cast<llvm::ConstantArray>(Base))
874        for (unsigned i = 0; i != NumElements; ++i)
875          Elts.push_back(Array->getOperand(i));
876      else
877        return nullptr; // FIXME: other array types not implemented
878
879      llvm::Constant *fillC = nullptr;
880      if (Expr *filler = Updater->getArrayFiller())
881        if (!isa<NoInitExpr>(filler))
882          fillC = CGM.EmitConstantExpr(filler, filler->getType(), CGF);
883      bool RewriteType = (fillC && fillC->getType() != ElemType);
884
885      for (unsigned i = 0; i != NumElements; ++i) {
886        Expr *Init = nullptr;
887        if (i < NumInitElements)
888          Init = Updater->getInit(i);
889
890        if (!Init && fillC)
891          Elts[i] = fillC;
892        else if (!Init || isa<NoInitExpr>(Init))
893          ; // Do nothing.
894        else if (InitListExpr *ChildILE = dyn_cast<InitListExpr>(Init))
895          Elts[i] = EmitDesignatedInitUpdater(Elts[i], ChildILE);
896        else
897          Elts[i] = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
898
899       if (!Elts[i])
900          return nullptr;
901        RewriteType |= (Elts[i]->getType() != ElemType);
902      }
903
904      if (RewriteType) {
905        std::vector<llvm::Type *> Types;
906        Types.reserve(NumElements);
907        for (unsigned i = 0; i != NumElements; ++i)
908          Types.push_back(Elts[i]->getType());
909        llvm::StructType *SType = llvm::StructType::get(AType->getContext(),
910                                                        Types, true);
911        return llvm::ConstantStruct::get(SType, Elts);
912      }
913
914      return llvm::ConstantArray::get(AType, Elts);
915    }
916
917    if (ExprType->isRecordType())
918      return ConstStructBuilder::BuildStruct(CGM, CGF, this,
919                 dyn_cast<llvm::ConstantStruct>(Base), Updater);
920
921    return nullptr;
922  }
923
924  llvm::Constant *VisitDesignatedInitUpdateExpr(DesignatedInitUpdateExpr *E) {
925    return EmitDesignatedInitUpdater(
926               CGM.EmitConstantExpr(E->getBase(), E->getType(), CGF),
927               E->getUpdater());
928  }
929
930  llvm::Constant *VisitCXXConstructExpr(CXXConstructExpr *E) {
931    if (!E->getConstructor()->isTrivial())
932      return nullptr;
933
934    QualType Ty = E->getType();
935
936    // FIXME: We should not have to call getBaseElementType here.
937    const RecordType *RT =
938      CGM.getContext().getBaseElementType(Ty)->getAs<RecordType>();
939    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
940
941    // If the class doesn't have a trivial destructor, we can't emit it as a
942    // constant expr.
943    if (!RD->hasTrivialDestructor())
944      return nullptr;
945
946    // Only copy and default constructors can be trivial.
947
948
949    if (E->getNumArgs()) {
950      assert(E->getNumArgs() == 1 && "trivial ctor with > 1 argument");
951      assert(E->getConstructor()->isCopyOrMoveConstructor() &&
952             "trivial ctor has argument but isn't a copy/move ctor");
953
954      Expr *Arg = E->getArg(0);
955      assert(CGM.getContext().hasSameUnqualifiedType(Ty, Arg->getType()) &&
956             "argument to copy ctor is of wrong type");
957
958      return Visit(Arg);
959    }
960
961    return CGM.EmitNullConstant(Ty);
962  }
963
964  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
965    return CGM.GetConstantArrayFromStringLiteral(E);
966  }
967
968  llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
969    // This must be an @encode initializing an array in a static initializer.
970    // Don't emit it as the address of the string, emit the string data itself
971    // as an inline array.
972    std::string Str;
973    CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
974    QualType T = E->getType();
975    if (T->getTypeClass() == Type::TypeOfExpr)
976      T = cast<TypeOfExprType>(T)->getUnderlyingExpr()->getType();
977    const ConstantArrayType *CAT = cast<ConstantArrayType>(T);
978
979    // Resize the string to the right size, adding zeros at the end, or
980    // truncating as needed.
981    Str.resize(CAT->getSize().getZExtValue(), '\0');
982    return llvm::ConstantDataArray::getString(VMContext, Str, false);
983  }
984
985  llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
986    return Visit(E->getSubExpr());
987  }
988
989  // Utility methods
990  llvm::Type *ConvertType(QualType T) {
991    return CGM.getTypes().ConvertType(T);
992  }
993
994public:
995  ConstantAddress EmitLValue(APValue::LValueBase LVBase) {
996    if (const ValueDecl *Decl = LVBase.dyn_cast<const ValueDecl*>()) {
997      if (Decl->hasAttr<WeakRefAttr>())
998        return CGM.GetWeakRefReference(Decl);
999      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
1000        return ConstantAddress(CGM.GetAddrOfFunction(FD), CharUnits::One());
1001      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
1002        // We can never refer to a variable with local storage.
1003        if (!VD->hasLocalStorage()) {
1004          CharUnits Align = CGM.getContext().getDeclAlign(VD);
1005          if (VD->isFileVarDecl() || VD->hasExternalStorage())
1006            return ConstantAddress(CGM.GetAddrOfGlobalVar(VD), Align);
1007          else if (VD->isLocalVarDecl()) {
1008            auto Ptr = CGM.getOrCreateStaticVarDecl(
1009                *VD, CGM.getLLVMLinkageVarDefinition(VD, /*isConstant=*/false));
1010            return ConstantAddress(Ptr, Align);
1011          }
1012        }
1013      }
1014      return ConstantAddress::invalid();
1015    }
1016
1017    Expr *E = const_cast<Expr*>(LVBase.get<const Expr*>());
1018    switch (E->getStmtClass()) {
1019    default: break;
1020    case Expr::CompoundLiteralExprClass: {
1021      // Note that due to the nature of compound literals, this is guaranteed
1022      // to be the only use of the variable, so we just generate it here.
1023      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
1024      llvm::Constant* C = CGM.EmitConstantExpr(CLE->getInitializer(),
1025                                               CLE->getType(), CGF);
1026      // FIXME: "Leaked" on failure.
1027      if (!C) return ConstantAddress::invalid();
1028
1029      CharUnits Align = CGM.getContext().getTypeAlignInChars(E->getType());
1030
1031      auto GV = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
1032                                     E->getType().isConstant(CGM.getContext()),
1033                                     llvm::GlobalValue::InternalLinkage,
1034                                     C, ".compoundliteral", nullptr,
1035                                     llvm::GlobalVariable::NotThreadLocal,
1036                          CGM.getContext().getTargetAddressSpace(E->getType()));
1037      GV->setAlignment(Align.getQuantity());
1038      return ConstantAddress(GV, Align);
1039    }
1040    case Expr::StringLiteralClass:
1041      return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
1042    case Expr::ObjCEncodeExprClass:
1043      return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
1044    case Expr::ObjCStringLiteralClass: {
1045      ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
1046      ConstantAddress C =
1047          CGM.getObjCRuntime().GenerateConstantString(SL->getString());
1048      return C.getElementBitCast(ConvertType(E->getType()));
1049    }
1050    case Expr::PredefinedExprClass: {
1051      unsigned Type = cast<PredefinedExpr>(E)->getIdentType();
1052      if (CGF) {
1053        LValue Res = CGF->EmitPredefinedLValue(cast<PredefinedExpr>(E));
1054        return cast<ConstantAddress>(Res.getAddress());
1055      } else if (Type == PredefinedExpr::PrettyFunction) {
1056        return CGM.GetAddrOfConstantCString("top level", ".tmp");
1057      }
1058
1059      return CGM.GetAddrOfConstantCString("", ".tmp");
1060    }
1061    case Expr::AddrLabelExprClass: {
1062      assert(CGF && "Invalid address of label expression outside function.");
1063      llvm::Constant *Ptr =
1064        CGF->GetAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
1065      Ptr = llvm::ConstantExpr::getBitCast(Ptr, ConvertType(E->getType()));
1066      return ConstantAddress(Ptr, CharUnits::One());
1067    }
1068    case Expr::CallExprClass: {
1069      CallExpr* CE = cast<CallExpr>(E);
1070      unsigned builtin = CE->getBuiltinCallee();
1071      if (builtin !=
1072            Builtin::BI__builtin___CFStringMakeConstantString &&
1073          builtin !=
1074            Builtin::BI__builtin___NSStringMakeConstantString)
1075        break;
1076      const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
1077      const StringLiteral *Literal = cast<StringLiteral>(Arg);
1078      if (builtin ==
1079            Builtin::BI__builtin___NSStringMakeConstantString) {
1080        return CGM.getObjCRuntime().GenerateConstantString(Literal);
1081      }
1082      // FIXME: need to deal with UCN conversion issues.
1083      return CGM.GetAddrOfConstantCFString(Literal);
1084    }
1085    case Expr::BlockExprClass: {
1086      std::string FunctionName;
1087      if (CGF)
1088        FunctionName = CGF->CurFn->getName();
1089      else
1090        FunctionName = "global";
1091
1092      // This is not really an l-value.
1093      llvm::Constant *Ptr =
1094        CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
1095      return ConstantAddress(Ptr, CGM.getPointerAlign());
1096    }
1097    case Expr::CXXTypeidExprClass: {
1098      CXXTypeidExpr *Typeid = cast<CXXTypeidExpr>(E);
1099      QualType T;
1100      if (Typeid->isTypeOperand())
1101        T = Typeid->getTypeOperand(CGM.getContext());
1102      else
1103        T = Typeid->getExprOperand()->getType();
1104      return ConstantAddress(CGM.GetAddrOfRTTIDescriptor(T),
1105                             CGM.getPointerAlign());
1106    }
1107    case Expr::CXXUuidofExprClass: {
1108      return CGM.GetAddrOfUuidDescriptor(cast<CXXUuidofExpr>(E));
1109    }
1110    case Expr::MaterializeTemporaryExprClass: {
1111      MaterializeTemporaryExpr *MTE = cast<MaterializeTemporaryExpr>(E);
1112      assert(MTE->getStorageDuration() == SD_Static);
1113      SmallVector<const Expr *, 2> CommaLHSs;
1114      SmallVector<SubobjectAdjustment, 2> Adjustments;
1115      const Expr *Inner = MTE->GetTemporaryExpr()
1116          ->skipRValueSubobjectAdjustments(CommaLHSs, Adjustments);
1117      return CGM.GetAddrOfGlobalTemporary(MTE, Inner);
1118    }
1119    }
1120
1121    return ConstantAddress::invalid();
1122  }
1123};
1124
1125}  // end anonymous namespace.
1126
1127bool ConstStructBuilder::Build(ConstExprEmitter *Emitter,
1128                               llvm::ConstantStruct *Base,
1129                               InitListExpr *Updater) {
1130  assert(Base && "base expression should not be empty");
1131
1132  QualType ExprType = Updater->getType();
1133  RecordDecl *RD = ExprType->getAs<RecordType>()->getDecl();
1134  const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
1135  const llvm::StructLayout *BaseLayout = CGM.getDataLayout().getStructLayout(
1136                                           Base->getType());
1137  unsigned FieldNo = -1;
1138  unsigned ElementNo = 0;
1139
1140  // Bail out if we have base classes. We could support these, but they only
1141  // arise in C++1z where we will have already constant folded most interesting
1142  // cases. FIXME: There are still a few more cases we can handle this way.
1143  if (auto *CXXRD = dyn_cast<CXXRecordDecl>(RD))
1144    if (CXXRD->getNumBases())
1145      return false;
1146
1147  for (FieldDecl *Field : RD->fields()) {
1148    ++FieldNo;
1149
1150    if (RD->isUnion() && Updater->getInitializedFieldInUnion() != Field)
1151      continue;
1152
1153    // Skip anonymous bitfields.
1154    if (Field->isUnnamedBitfield())
1155      continue;
1156
1157    llvm::Constant *EltInit = Base->getOperand(ElementNo);
1158
1159    // Bail out if the type of the ConstantStruct does not have the same layout
1160    // as the type of the InitListExpr.
1161    if (CGM.getTypes().ConvertType(Field->getType()) != EltInit->getType() ||
1162        Layout.getFieldOffset(ElementNo) !=
1163          BaseLayout->getElementOffsetInBits(ElementNo))
1164      return false;
1165
1166    // Get the initializer. If we encounter an empty field or a NoInitExpr,
1167    // we use values from the base expression.
1168    Expr *Init = nullptr;
1169    if (ElementNo < Updater->getNumInits())
1170      Init = Updater->getInit(ElementNo);
1171
1172    if (!Init || isa<NoInitExpr>(Init))
1173      ; // Do nothing.
1174    else if (InitListExpr *ChildILE = dyn_cast<InitListExpr>(Init))
1175      EltInit = Emitter->EmitDesignatedInitUpdater(EltInit, ChildILE);
1176    else
1177      EltInit = CGM.EmitConstantExpr(Init, Field->getType(), CGF);
1178
1179    ++ElementNo;
1180
1181    if (!EltInit)
1182      return false;
1183
1184    if (!Field->isBitField())
1185      AppendField(Field, Layout.getFieldOffset(FieldNo), EltInit);
1186    else if (llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(EltInit))
1187      AppendBitField(Field, Layout.getFieldOffset(FieldNo), CI);
1188    else
1189      // Initializing a bitfield with a non-trivial constant?
1190      return false;
1191  }
1192
1193  return true;
1194}
1195
1196llvm::Constant *CodeGenModule::EmitConstantInit(const VarDecl &D,
1197                                                CodeGenFunction *CGF) {
1198  // Make a quick check if variable can be default NULL initialized
1199  // and avoid going through rest of code which may do, for c++11,
1200  // initialization of memory to all NULLs.
1201  if (!D.hasLocalStorage()) {
1202    QualType Ty = D.getType();
1203    if (Ty->isArrayType())
1204      Ty = Context.getBaseElementType(Ty);
1205    if (Ty->isRecordType())
1206      if (const CXXConstructExpr *E =
1207          dyn_cast_or_null<CXXConstructExpr>(D.getInit())) {
1208        const CXXConstructorDecl *CD = E->getConstructor();
1209        if (CD->isTrivial() && CD->isDefaultConstructor())
1210          return EmitNullConstant(D.getType());
1211      }
1212  }
1213
1214  if (const APValue *Value = D.evaluateValue())
1215    return EmitConstantValueForMemory(*Value, D.getType(), CGF);
1216
1217  // FIXME: Implement C++11 [basic.start.init]p2: if the initializer of a
1218  // reference is a constant expression, and the reference binds to a temporary,
1219  // then constant initialization is performed. ConstExprEmitter will
1220  // incorrectly emit a prvalue constant in this case, and the calling code
1221  // interprets that as the (pointer) value of the reference, rather than the
1222  // desired value of the referee.
1223  if (D.getType()->isReferenceType())
1224    return nullptr;
1225
1226  const Expr *E = D.getInit();
1227  assert(E && "No initializer to emit");
1228
1229  llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
1230  if (C && C->getType()->isIntegerTy(1)) {
1231    llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
1232    C = llvm::ConstantExpr::getZExt(C, BoolTy);
1233  }
1234  return C;
1235}
1236
1237llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
1238                                                QualType DestType,
1239                                                CodeGenFunction *CGF) {
1240  Expr::EvalResult Result;
1241
1242  bool Success = false;
1243
1244  if (DestType->isReferenceType())
1245    Success = E->EvaluateAsLValue(Result, Context);
1246  else
1247    Success = E->EvaluateAsRValue(Result, Context);
1248
1249  llvm::Constant *C = nullptr;
1250  if (Success && !Result.HasSideEffects)
1251    C = EmitConstantValue(Result.Val, DestType, CGF);
1252  else
1253    C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
1254
1255  if (C && C->getType()->isIntegerTy(1)) {
1256    llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
1257    C = llvm::ConstantExpr::getZExt(C, BoolTy);
1258  }
1259  return C;
1260}
1261
1262llvm::Constant *CodeGenModule::EmitConstantValue(const APValue &Value,
1263                                                 QualType DestType,
1264                                                 CodeGenFunction *CGF) {
1265  // For an _Atomic-qualified constant, we may need to add tail padding.
1266  if (auto *AT = DestType->getAs<AtomicType>()) {
1267    QualType InnerType = AT->getValueType();
1268    auto *Inner = EmitConstantValue(Value, InnerType, CGF);
1269
1270    uint64_t InnerSize = Context.getTypeSize(InnerType);
1271    uint64_t OuterSize = Context.getTypeSize(DestType);
1272    if (InnerSize == OuterSize)
1273      return Inner;
1274
1275    assert(InnerSize < OuterSize && "emitted over-large constant for atomic");
1276    llvm::Constant *Elts[] = {
1277      Inner,
1278      llvm::ConstantAggregateZero::get(
1279          llvm::ArrayType::get(Int8Ty, (OuterSize - InnerSize) / 8))
1280    };
1281    return llvm::ConstantStruct::getAnon(Elts);
1282  }
1283
1284  switch (Value.getKind()) {
1285  case APValue::Uninitialized:
1286    llvm_unreachable("Constant expressions should be initialized.");
1287  case APValue::LValue: {
1288    llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
1289    llvm::Constant *Offset =
1290      llvm::ConstantInt::get(Int64Ty, Value.getLValueOffset().getQuantity());
1291
1292    llvm::Constant *C = nullptr;
1293    if (APValue::LValueBase LVBase = Value.getLValueBase()) {
1294      // An array can be represented as an lvalue referring to the base.
1295      if (isa<llvm::ArrayType>(DestTy)) {
1296        assert(Offset->isNullValue() && "offset on array initializer");
1297        return ConstExprEmitter(*this, CGF).Visit(
1298          const_cast<Expr*>(LVBase.get<const Expr*>()));
1299      }
1300
1301      C = ConstExprEmitter(*this, CGF).EmitLValue(LVBase).getPointer();
1302
1303      // Apply offset if necessary.
1304      if (!Offset->isNullValue()) {
1305        unsigned AS = C->getType()->getPointerAddressSpace();
1306        llvm::Type *CharPtrTy = Int8Ty->getPointerTo(AS);
1307        llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, CharPtrTy);
1308        Casted = llvm::ConstantExpr::getGetElementPtr(Int8Ty, Casted, Offset);
1309        C = llvm::ConstantExpr::getPointerCast(Casted, C->getType());
1310      }
1311
1312      // Convert to the appropriate type; this could be an lvalue for
1313      // an integer.
1314      if (isa<llvm::PointerType>(DestTy))
1315        return llvm::ConstantExpr::getPointerCast(C, DestTy);
1316
1317      return llvm::ConstantExpr::getPtrToInt(C, DestTy);
1318    } else {
1319      C = Offset;
1320
1321      // Convert to the appropriate type; this could be an lvalue for
1322      // an integer.
1323      if (isa<llvm::PointerType>(DestTy)) {
1324        // Convert the integer to a pointer-sized integer before converting it
1325        // to a pointer.
1326        C = llvm::ConstantExpr::getIntegerCast(
1327            C, getDataLayout().getIntPtrType(DestTy),
1328            /*isSigned=*/false);
1329        return llvm::ConstantExpr::getIntToPtr(C, DestTy);
1330      }
1331
1332      // If the types don't match this should only be a truncate.
1333      if (C->getType() != DestTy)
1334        return llvm::ConstantExpr::getTrunc(C, DestTy);
1335
1336      return C;
1337    }
1338  }
1339  case APValue::Int:
1340    return llvm::ConstantInt::get(VMContext, Value.getInt());
1341  case APValue::ComplexInt: {
1342    llvm::Constant *Complex[2];
1343
1344    Complex[0] = llvm::ConstantInt::get(VMContext,
1345                                        Value.getComplexIntReal());
1346    Complex[1] = llvm::ConstantInt::get(VMContext,
1347                                        Value.getComplexIntImag());
1348
1349    // FIXME: the target may want to specify that this is packed.
1350    llvm::StructType *STy = llvm::StructType::get(Complex[0]->getType(),
1351                                                  Complex[1]->getType(),
1352                                                  nullptr);
1353    return llvm::ConstantStruct::get(STy, Complex);
1354  }
1355  case APValue::Float: {
1356    const llvm::APFloat &Init = Value.getFloat();
1357    if (&Init.getSemantics() == &llvm::APFloat::IEEEhalf &&
1358        !Context.getLangOpts().NativeHalfType &&
1359        !Context.getLangOpts().HalfArgsAndReturns)
1360      return llvm::ConstantInt::get(VMContext, Init.bitcastToAPInt());
1361    else
1362      return llvm::ConstantFP::get(VMContext, Init);
1363  }
1364  case APValue::ComplexFloat: {
1365    llvm::Constant *Complex[2];
1366
1367    Complex[0] = llvm::ConstantFP::get(VMContext,
1368                                       Value.getComplexFloatReal());
1369    Complex[1] = llvm::ConstantFP::get(VMContext,
1370                                       Value.getComplexFloatImag());
1371
1372    // FIXME: the target may want to specify that this is packed.
1373    llvm::StructType *STy = llvm::StructType::get(Complex[0]->getType(),
1374                                                  Complex[1]->getType(),
1375                                                  nullptr);
1376    return llvm::ConstantStruct::get(STy, Complex);
1377  }
1378  case APValue::Vector: {
1379    unsigned NumElts = Value.getVectorLength();
1380    SmallVector<llvm::Constant *, 4> Inits(NumElts);
1381
1382    for (unsigned I = 0; I != NumElts; ++I) {
1383      const APValue &Elt = Value.getVectorElt(I);
1384      if (Elt.isInt())
1385        Inits[I] = llvm::ConstantInt::get(VMContext, Elt.getInt());
1386      else if (Elt.isFloat())
1387        Inits[I] = llvm::ConstantFP::get(VMContext, Elt.getFloat());
1388      else
1389        llvm_unreachable("unsupported vector element type");
1390    }
1391    return llvm::ConstantVector::get(Inits);
1392  }
1393  case APValue::AddrLabelDiff: {
1394    const AddrLabelExpr *LHSExpr = Value.getAddrLabelDiffLHS();
1395    const AddrLabelExpr *RHSExpr = Value.getAddrLabelDiffRHS();
1396    llvm::Constant *LHS = EmitConstantExpr(LHSExpr, LHSExpr->getType(), CGF);
1397    llvm::Constant *RHS = EmitConstantExpr(RHSExpr, RHSExpr->getType(), CGF);
1398
1399    // Compute difference
1400    llvm::Type *ResultType = getTypes().ConvertType(DestType);
1401    LHS = llvm::ConstantExpr::getPtrToInt(LHS, IntPtrTy);
1402    RHS = llvm::ConstantExpr::getPtrToInt(RHS, IntPtrTy);
1403    llvm::Constant *AddrLabelDiff = llvm::ConstantExpr::getSub(LHS, RHS);
1404
1405    // LLVM is a bit sensitive about the exact format of the
1406    // address-of-label difference; make sure to truncate after
1407    // the subtraction.
1408    return llvm::ConstantExpr::getTruncOrBitCast(AddrLabelDiff, ResultType);
1409  }
1410  case APValue::Struct:
1411  case APValue::Union:
1412    return ConstStructBuilder::BuildStruct(*this, CGF, Value, DestType);
1413  case APValue::Array: {
1414    const ArrayType *CAT = Context.getAsArrayType(DestType);
1415    unsigned NumElements = Value.getArraySize();
1416    unsigned NumInitElts = Value.getArrayInitializedElts();
1417
1418    // Emit array filler, if there is one.
1419    llvm::Constant *Filler = nullptr;
1420    if (Value.hasArrayFiller())
1421      Filler = EmitConstantValueForMemory(Value.getArrayFiller(),
1422                                          CAT->getElementType(), CGF);
1423
1424    // Emit initializer elements.
1425    llvm::Type *CommonElementType =
1426        getTypes().ConvertType(CAT->getElementType());
1427
1428    // Try to use a ConstantAggregateZero if we can.
1429    if (Filler && Filler->isNullValue() && !NumInitElts) {
1430      llvm::ArrayType *AType =
1431          llvm::ArrayType::get(CommonElementType, NumElements);
1432      return llvm::ConstantAggregateZero::get(AType);
1433    }
1434
1435    std::vector<llvm::Constant*> Elts;
1436    Elts.reserve(NumElements);
1437    for (unsigned I = 0; I < NumElements; ++I) {
1438      llvm::Constant *C = Filler;
1439      if (I < NumInitElts)
1440        C = EmitConstantValueForMemory(Value.getArrayInitializedElt(I),
1441                                       CAT->getElementType(), CGF);
1442      else
1443        assert(Filler && "Missing filler for implicit elements of initializer");
1444      if (I == 0)
1445        CommonElementType = C->getType();
1446      else if (C->getType() != CommonElementType)
1447        CommonElementType = nullptr;
1448      Elts.push_back(C);
1449    }
1450
1451    if (!CommonElementType) {
1452      // FIXME: Try to avoid packing the array
1453      std::vector<llvm::Type*> Types;
1454      Types.reserve(NumElements);
1455      for (unsigned i = 0, e = Elts.size(); i < e; ++i)
1456        Types.push_back(Elts[i]->getType());
1457      llvm::StructType *SType = llvm::StructType::get(VMContext, Types, true);
1458      return llvm::ConstantStruct::get(SType, Elts);
1459    }
1460
1461    llvm::ArrayType *AType =
1462      llvm::ArrayType::get(CommonElementType, NumElements);
1463    return llvm::ConstantArray::get(AType, Elts);
1464  }
1465  case APValue::MemberPointer:
1466    return getCXXABI().EmitMemberPointer(Value, DestType);
1467  }
1468  llvm_unreachable("Unknown APValue kind");
1469}
1470
1471llvm::Constant *
1472CodeGenModule::EmitConstantValueForMemory(const APValue &Value,
1473                                          QualType DestType,
1474                                          CodeGenFunction *CGF) {
1475  llvm::Constant *C = EmitConstantValue(Value, DestType, CGF);
1476  if (C->getType()->isIntegerTy(1)) {
1477    llvm::Type *BoolTy = getTypes().ConvertTypeForMem(DestType);
1478    C = llvm::ConstantExpr::getZExt(C, BoolTy);
1479  }
1480  return C;
1481}
1482
1483ConstantAddress
1484CodeGenModule::GetAddrOfConstantCompoundLiteral(const CompoundLiteralExpr *E) {
1485  assert(E->isFileScope() && "not a file-scope compound literal expr");
1486  return ConstExprEmitter(*this, nullptr).EmitLValue(E);
1487}
1488
1489llvm::Constant *
1490CodeGenModule::getMemberPointerConstant(const UnaryOperator *uo) {
1491  // Member pointer constants always have a very particular form.
1492  const MemberPointerType *type = cast<MemberPointerType>(uo->getType());
1493  const ValueDecl *decl = cast<DeclRefExpr>(uo->getSubExpr())->getDecl();
1494
1495  // A member function pointer.
1496  if (const CXXMethodDecl *method = dyn_cast<CXXMethodDecl>(decl))
1497    return getCXXABI().EmitMemberFunctionPointer(method);
1498
1499  // Otherwise, a member data pointer.
1500  uint64_t fieldOffset = getContext().getFieldOffset(decl);
1501  CharUnits chars = getContext().toCharUnitsFromBits((int64_t) fieldOffset);
1502  return getCXXABI().EmitMemberDataPointer(type, chars);
1503}
1504
1505static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
1506                                               llvm::Type *baseType,
1507                                               const CXXRecordDecl *base);
1508
1509static llvm::Constant *EmitNullConstant(CodeGenModule &CGM,
1510                                        const CXXRecordDecl *record,
1511                                        bool asCompleteObject) {
1512  const CGRecordLayout &layout = CGM.getTypes().getCGRecordLayout(record);
1513  llvm::StructType *structure =
1514    (asCompleteObject ? layout.getLLVMType()
1515                      : layout.getBaseSubobjectLLVMType());
1516
1517  unsigned numElements = structure->getNumElements();
1518  std::vector<llvm::Constant *> elements(numElements);
1519
1520  // Fill in all the bases.
1521  for (const auto &I : record->bases()) {
1522    if (I.isVirtual()) {
1523      // Ignore virtual bases; if we're laying out for a complete
1524      // object, we'll lay these out later.
1525      continue;
1526    }
1527
1528    const CXXRecordDecl *base =
1529      cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
1530
1531    // Ignore empty bases.
1532    if (base->isEmpty())
1533      continue;
1534
1535    unsigned fieldIndex = layout.getNonVirtualBaseLLVMFieldNo(base);
1536    llvm::Type *baseType = structure->getElementType(fieldIndex);
1537    elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
1538  }
1539
1540  // Fill in all the fields.
1541  for (const auto *Field : record->fields()) {
1542    // Fill in non-bitfields. (Bitfields always use a zero pattern, which we
1543    // will fill in later.)
1544    if (!Field->isBitField()) {
1545      unsigned fieldIndex = layout.getLLVMFieldNo(Field);
1546      elements[fieldIndex] = CGM.EmitNullConstant(Field->getType());
1547    }
1548
1549    // For unions, stop after the first named field.
1550    if (record->isUnion()) {
1551      if (Field->getIdentifier())
1552        break;
1553      if (const auto *FieldRD =
1554              dyn_cast_or_null<RecordDecl>(Field->getType()->getAsTagDecl()))
1555        if (FieldRD->findFirstNamedDataMember())
1556          break;
1557    }
1558  }
1559
1560  // Fill in the virtual bases, if we're working with the complete object.
1561  if (asCompleteObject) {
1562    for (const auto &I : record->vbases()) {
1563      const CXXRecordDecl *base =
1564        cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
1565
1566      // Ignore empty bases.
1567      if (base->isEmpty())
1568        continue;
1569
1570      unsigned fieldIndex = layout.getVirtualBaseIndex(base);
1571
1572      // We might have already laid this field out.
1573      if (elements[fieldIndex]) continue;
1574
1575      llvm::Type *baseType = structure->getElementType(fieldIndex);
1576      elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
1577    }
1578  }
1579
1580  // Now go through all other fields and zero them out.
1581  for (unsigned i = 0; i != numElements; ++i) {
1582    if (!elements[i])
1583      elements[i] = llvm::Constant::getNullValue(structure->getElementType(i));
1584  }
1585
1586  return llvm::ConstantStruct::get(structure, elements);
1587}
1588
1589/// Emit the null constant for a base subobject.
1590static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
1591                                               llvm::Type *baseType,
1592                                               const CXXRecordDecl *base) {
1593  const CGRecordLayout &baseLayout = CGM.getTypes().getCGRecordLayout(base);
1594
1595  // Just zero out bases that don't have any pointer to data members.
1596  if (baseLayout.isZeroInitializableAsBase())
1597    return llvm::Constant::getNullValue(baseType);
1598
1599  // Otherwise, we can just use its null constant.
1600  return EmitNullConstant(CGM, base, /*asCompleteObject=*/false);
1601}
1602
1603llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
1604  if (getTypes().isZeroInitializable(T))
1605    return llvm::Constant::getNullValue(getTypes().ConvertTypeForMem(T));
1606
1607  if (const ConstantArrayType *CAT = Context.getAsConstantArrayType(T)) {
1608    llvm::ArrayType *ATy =
1609      cast<llvm::ArrayType>(getTypes().ConvertTypeForMem(T));
1610
1611    QualType ElementTy = CAT->getElementType();
1612
1613    llvm::Constant *Element = EmitNullConstant(ElementTy);
1614    unsigned NumElements = CAT->getSize().getZExtValue();
1615    SmallVector<llvm::Constant *, 8> Array(NumElements, Element);
1616    return llvm::ConstantArray::get(ATy, Array);
1617  }
1618
1619  if (const RecordType *RT = T->getAs<RecordType>()) {
1620    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
1621    return ::EmitNullConstant(*this, RD, /*complete object*/ true);
1622  }
1623
1624  assert(T->isMemberDataPointerType() &&
1625         "Should only see pointers to data members here!");
1626
1627  return getCXXABI().EmitNullMemberPointer(T->castAs<MemberPointerType>());
1628}
1629
1630llvm::Constant *
1631CodeGenModule::EmitNullConstantForBase(const CXXRecordDecl *Record) {
1632  return ::EmitNullConstant(*this, Record, false);
1633}
1634