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 "clang/AST/APValue.h"
18 #include "clang/AST/ASTContext.h"
19 #include "clang/AST/RecordLayout.h"
20 #include "clang/AST/StmtVisitor.h"
21 #include "clang/Basic/Builtins.h"
22 #include "llvm/Constants.h"
23 #include "llvm/Function.h"
24 #include "llvm/GlobalVariable.h"
25 #include "llvm/Support/Compiler.h"
26 #include "llvm/Target/TargetData.h"
27 using namespace clang;
28 using namespace CodeGen;
29 
30 namespace  {
31 
32 class VISIBILITY_HIDDEN ConstStructBuilder {
33   CodeGenModule &CGM;
34   CodeGenFunction *CGF;
35 
36   bool Packed;
37 
38   unsigned NextFieldOffsetInBytes;
39 
40   std::vector<llvm::Constant *> Elements;
41 
42   ConstStructBuilder(CodeGenModule &CGM, CodeGenFunction *CGF)
43     : CGM(CGM), CGF(CGF), Packed(false), NextFieldOffsetInBytes(0) { }
44 
45   bool AppendField(const FieldDecl *Field, uint64_t FieldOffset,
46                    const Expr *InitExpr) {
47     uint64_t FieldOffsetInBytes = FieldOffset / 8;
48 
49     assert(NextFieldOffsetInBytes <= FieldOffsetInBytes
50            && "Field offset mismatch!");
51 
52     // Emit the field.
53     llvm::Constant *C = CGM.EmitConstantExpr(InitExpr, Field->getType(), CGF);
54     if (!C)
55       return false;
56 
57     unsigned FieldAlignment = getAlignment(C);
58 
59     // Round up the field offset to the alignment of the field type.
60     uint64_t AlignedNextFieldOffsetInBytes =
61       llvm::RoundUpToAlignment(NextFieldOffsetInBytes, FieldAlignment);
62 
63     if (AlignedNextFieldOffsetInBytes > FieldOffsetInBytes) {
64       std::vector<llvm::Constant *> PackedElements;
65 
66       assert(!Packed && "Alignment is wrong even with a packed struct!");
67 
68       // Convert the struct to a packed struct.
69       uint64_t ElementOffsetInBytes = 0;
70 
71       for (unsigned i = 0, e = Elements.size(); i != e; ++i) {
72         llvm::Constant *C = Elements[i];
73 
74         unsigned ElementAlign =
75           CGM.getTargetData().getABITypeAlignment(C->getType());
76         uint64_t AlignedElementOffsetInBytes =
77           llvm::RoundUpToAlignment(ElementOffsetInBytes, ElementAlign);
78 
79         if (AlignedElementOffsetInBytes > ElementOffsetInBytes) {
80           // We need some padding.
81           uint64_t NumBytes =
82             AlignedElementOffsetInBytes - ElementOffsetInBytes;
83 
84           const llvm::Type *Ty = llvm::Type::Int8Ty;
85           if (NumBytes > 1)
86             Ty = llvm::ArrayType::get(Ty, NumBytes);
87 
88           llvm::Constant *Padding = llvm::Constant::getNullValue(Ty);
89           PackedElements.push_back(Padding);
90           ElementOffsetInBytes += getSizeInBytes(Padding);
91         }
92 
93         PackedElements.push_back(C);
94         ElementOffsetInBytes += getSizeInBytes(C);
95       }
96 
97       assert(ElementOffsetInBytes == NextFieldOffsetInBytes &&
98              "Packing the struct changed its size!");
99 
100       Elements = PackedElements;
101       Packed = true;
102       AlignedNextFieldOffsetInBytes = NextFieldOffsetInBytes;
103     }
104 
105     if (AlignedNextFieldOffsetInBytes < FieldOffsetInBytes) {
106       // We need to append padding.
107       AppendPadding(FieldOffsetInBytes - NextFieldOffsetInBytes);
108 
109       assert(NextFieldOffsetInBytes == FieldOffsetInBytes &&
110              "Did not add enough padding!");
111 
112       AlignedNextFieldOffsetInBytes = NextFieldOffsetInBytes;
113     }
114 
115     // Add the field.
116     Elements.push_back(C);
117     NextFieldOffsetInBytes = AlignedNextFieldOffsetInBytes + getSizeInBytes(C);
118 
119     return true;
120   }
121 
122   bool AppendBitField(const FieldDecl *Field, uint64_t FieldOffset,
123                       const Expr *InitExpr) {
124     llvm::ConstantInt *CI =
125       cast_or_null<llvm::ConstantInt>(CGM.EmitConstantExpr(InitExpr,
126                                                            Field->getType(),
127                                                            CGF));
128     // FIXME: Can this ever happen?
129     if (!CI)
130       return false;
131 
132     if (FieldOffset > NextFieldOffsetInBytes * 8) {
133       // We need to add padding.
134       uint64_t NumBytes =
135         llvm::RoundUpToAlignment(FieldOffset -
136                                  NextFieldOffsetInBytes * 8, 8) / 8;
137 
138       AppendPadding(NumBytes);
139     }
140 
141     uint64_t FieldSize =
142       Field->getBitWidth()->EvaluateAsInt(CGM.getContext()).getZExtValue();
143 
144     llvm::APInt FieldValue = CI->getValue();
145 
146     // Promote the size of FieldValue if necessary
147     // FIXME: This should never occur, but currently it can because initializer
148     // constants are cast to bool, and because clang is not enforcing bitfield
149     // width limits.
150     if (FieldSize > FieldValue.getBitWidth())
151       FieldValue.zext(FieldSize);
152 
153     // Truncate the size of FieldValue to the bit field size.
154     if (FieldSize < FieldValue.getBitWidth())
155       FieldValue.trunc(FieldSize);
156 
157     if (FieldOffset < NextFieldOffsetInBytes * 8) {
158       // Either part of the field or the entire field can go into the previous
159       // byte.
160       assert(!Elements.empty() && "Elements can't be empty!");
161 
162       unsigned BitsInPreviousByte =
163         NextFieldOffsetInBytes * 8 - FieldOffset;
164 
165       bool FitsCompletelyInPreviousByte =
166         BitsInPreviousByte >= FieldValue.getBitWidth();
167 
168       llvm::APInt Tmp = FieldValue;
169 
170       if (!FitsCompletelyInPreviousByte) {
171         unsigned NewFieldWidth = FieldSize - BitsInPreviousByte;
172 
173         if (CGM.getTargetData().isBigEndian()) {
174           Tmp = Tmp.lshr(NewFieldWidth);
175           Tmp.trunc(BitsInPreviousByte);
176 
177           // We want the remaining high bits.
178           FieldValue.trunc(NewFieldWidth);
179         } else {
180           Tmp.trunc(BitsInPreviousByte);
181 
182           // We want the remaining low bits.
183           FieldValue = FieldValue.lshr(BitsInPreviousByte);
184           FieldValue.trunc(NewFieldWidth);
185         }
186       }
187 
188       Tmp.zext(8);
189       if (CGM.getTargetData().isBigEndian()) {
190         if (FitsCompletelyInPreviousByte)
191           Tmp = Tmp.shl(BitsInPreviousByte - FieldValue.getBitWidth());
192       } else {
193         Tmp = Tmp.shl(8 - BitsInPreviousByte);
194       }
195 
196       // Or in the bits that go into the previous byte.
197       Tmp |= cast<llvm::ConstantInt>(Elements.back())->getValue();
198       Elements.back() = llvm::ConstantInt::get(CGM.getLLVMContext(), Tmp);
199 
200       if (FitsCompletelyInPreviousByte)
201         return true;
202     }
203 
204     while (FieldValue.getBitWidth() > 8) {
205       llvm::APInt Tmp;
206 
207       if (CGM.getTargetData().isBigEndian()) {
208         // We want the high bits.
209         Tmp = FieldValue;
210         Tmp = Tmp.lshr(Tmp.getBitWidth() - 8);
211         Tmp.trunc(8);
212       } else {
213         // We want the low bits.
214         Tmp = FieldValue;
215         Tmp.trunc(8);
216 
217         FieldValue = FieldValue.lshr(8);
218       }
219 
220       Elements.push_back(llvm::ConstantInt::get(CGM.getLLVMContext(), Tmp));
221       NextFieldOffsetInBytes++;
222 
223       FieldValue.trunc(FieldValue.getBitWidth() - 8);
224     }
225 
226     assert(FieldValue.getBitWidth() > 0 &&
227            "Should have at least one bit left!");
228     assert(FieldValue.getBitWidth() <= 8 &&
229            "Should not have more than a byte left!");
230 
231     if (FieldValue.getBitWidth() < 8) {
232       if (CGM.getTargetData().isBigEndian()) {
233         unsigned BitWidth = FieldValue.getBitWidth();
234 
235         FieldValue.zext(8);
236         FieldValue = FieldValue << (8 - BitWidth);
237       } else
238         FieldValue.zext(8);
239     }
240 
241     // Append the last element.
242     Elements.push_back(llvm::ConstantInt::get(CGM.getLLVMContext(),
243                                               FieldValue));
244     NextFieldOffsetInBytes++;
245     return true;
246   }
247 
248   void AppendPadding(uint64_t NumBytes) {
249     if (!NumBytes)
250       return;
251 
252     const llvm::Type *Ty = llvm::Type::Int8Ty;
253     if (NumBytes > 1)
254       Ty = llvm::ArrayType::get(Ty, NumBytes);
255 
256     llvm::Constant *C = llvm::Constant::getNullValue(Ty);
257     Elements.push_back(C);
258     assert(getAlignment(C) == 1 && "Padding must have 1 byte alignment!");
259 
260     NextFieldOffsetInBytes += getSizeInBytes(C);
261   }
262 
263   void AppendTailPadding(uint64_t RecordSize) {
264     assert(RecordSize % 8 == 0 && "Invalid record size!");
265 
266     uint64_t RecordSizeInBytes = RecordSize / 8;
267     assert(NextFieldOffsetInBytes <= RecordSizeInBytes && "Size mismatch!");
268 
269     unsigned NumPadBytes = RecordSizeInBytes - NextFieldOffsetInBytes;
270     AppendPadding(NumPadBytes);
271   }
272 
273   bool Build(const InitListExpr *ILE) {
274     RecordDecl *RD = ILE->getType()->getAs<RecordType>()->getDecl();
275     const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
276 
277     unsigned FieldNo = 0;
278     unsigned ElementNo = 0;
279     for (RecordDecl::field_iterator Field = RD->field_begin(),
280          FieldEnd = RD->field_end();
281          ElementNo < ILE->getNumInits() && Field != FieldEnd;
282          ++Field, ++FieldNo) {
283       if (Field->isBitField()) {
284         if (!Field->getIdentifier())
285           continue;
286 
287         if (!AppendBitField(*Field, Layout.getFieldOffset(FieldNo),
288                             ILE->getInit(ElementNo)))
289           return false;
290       } else {
291         if (!AppendField(*Field, Layout.getFieldOffset(FieldNo),
292                          ILE->getInit(ElementNo)))
293           return false;
294       }
295 
296       ElementNo++;
297     }
298 
299     uint64_t LayoutSizeInBytes = Layout.getSize() / 8;
300 
301     if (NextFieldOffsetInBytes > LayoutSizeInBytes) {
302       // If the struct is bigger than the size of the record type,
303       // we must have a flexible array member at the end.
304       assert(RD->hasFlexibleArrayMember() &&
305              "Must have flexible array member if struct is bigger than type!");
306 
307       // No tail padding is necessary.
308       return true;
309     }
310 
311     // Append tail padding if necessary.
312     AppendTailPadding(Layout.getSize());
313 
314     assert(Layout.getSize() / 8 == NextFieldOffsetInBytes &&
315            "Tail padding mismatch!");
316 
317     return true;
318   }
319 
320   unsigned getAlignment(const llvm::Constant *C) const {
321     if (Packed)
322       return 1;
323 
324     return CGM.getTargetData().getABITypeAlignment(C->getType());
325   }
326 
327   uint64_t getSizeInBytes(const llvm::Constant *C) const {
328     return CGM.getTargetData().getTypeAllocSize(C->getType());
329   }
330 
331 public:
332   static llvm::Constant *BuildStruct(CodeGenModule &CGM, CodeGenFunction *CGF,
333                                      const InitListExpr *ILE) {
334     ConstStructBuilder Builder(CGM, CGF);
335 
336     if (!Builder.Build(ILE))
337       return 0;
338 
339     llvm::Constant *Result =
340       llvm::ConstantStruct::get(Builder.Elements, Builder.Packed);
341 
342     assert(llvm::RoundUpToAlignment(Builder.NextFieldOffsetInBytes,
343                                     Builder.getAlignment(Result)) ==
344            Builder.getSizeInBytes(Result) && "Size mismatch!");
345 
346     return Result;
347   }
348 };
349 
350 class VISIBILITY_HIDDEN ConstExprEmitter :
351   public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
352   CodeGenModule &CGM;
353   CodeGenFunction *CGF;
354   llvm::LLVMContext &VMContext;
355 public:
356   ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
357     : CGM(cgm), CGF(cgf), VMContext(cgm.getLLVMContext()) {
358   }
359 
360   //===--------------------------------------------------------------------===//
361   //                            Visitor Methods
362   //===--------------------------------------------------------------------===//
363 
364   llvm::Constant *VisitStmt(Stmt *S) {
365     return 0;
366   }
367 
368   llvm::Constant *VisitParenExpr(ParenExpr *PE) {
369     return Visit(PE->getSubExpr());
370   }
371 
372   llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
373     return Visit(E->getInitializer());
374   }
375 
376   llvm::Constant *VisitCastExpr(CastExpr* E) {
377     // GCC cast to union extension
378     if (E->getType()->isUnionType()) {
379       const llvm::Type *Ty = ConvertType(E->getType());
380       Expr *SubExpr = E->getSubExpr();
381       return EmitUnion(CGM.EmitConstantExpr(SubExpr, SubExpr->getType(), CGF),
382                        Ty);
383     }
384     // Explicit and implicit no-op casts
385     QualType Ty = E->getType(), SubTy = E->getSubExpr()->getType();
386     if (CGM.getContext().hasSameUnqualifiedType(Ty, SubTy)) {
387       return Visit(E->getSubExpr());
388     }
389     return 0;
390   }
391 
392   llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
393     return Visit(DAE->getExpr());
394   }
395 
396   llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
397     std::vector<llvm::Constant*> Elts;
398     const llvm::ArrayType *AType =
399         cast<llvm::ArrayType>(ConvertType(ILE->getType()));
400     unsigned NumInitElements = ILE->getNumInits();
401     // FIXME: Check for wide strings
402     // FIXME: Check for NumInitElements exactly equal to 1??
403     if (NumInitElements > 0 &&
404         (isa<StringLiteral>(ILE->getInit(0)) ||
405          isa<ObjCEncodeExpr>(ILE->getInit(0))) &&
406         ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
407       return Visit(ILE->getInit(0));
408     const llvm::Type *ElemTy = AType->getElementType();
409     unsigned NumElements = AType->getNumElements();
410 
411     // Initialising an array requires us to automatically
412     // initialise any elements that have not been initialised explicitly
413     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
414 
415     // Copy initializer elements.
416     unsigned i = 0;
417     bool RewriteType = false;
418     for (; i < NumInitableElts; ++i) {
419       Expr *Init = ILE->getInit(i);
420       llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
421       if (!C)
422         return 0;
423       RewriteType |= (C->getType() != ElemTy);
424       Elts.push_back(C);
425     }
426 
427     // Initialize remaining array elements.
428     // FIXME: This doesn't handle member pointers correctly!
429     for (; i < NumElements; ++i)
430       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
431 
432     if (RewriteType) {
433       // FIXME: Try to avoid packing the array
434       std::vector<const llvm::Type*> Types;
435       for (unsigned i = 0; i < Elts.size(); ++i)
436         Types.push_back(Elts[i]->getType());
437       const llvm::StructType *SType = llvm::StructType::get(Types, true);
438       return llvm::ConstantStruct::get(SType, Elts);
439     }
440 
441     return llvm::ConstantArray::get(AType, Elts);
442   }
443 
444   void InsertBitfieldIntoStruct(std::vector<llvm::Constant*>& Elts,
445                                 FieldDecl* Field, Expr* E) {
446     // Calculate the value to insert
447     llvm::Constant *C = CGM.EmitConstantExpr(E, Field->getType(), CGF);
448     if (!C)
449       return;
450 
451     llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
452     if (!CI) {
453       CGM.ErrorUnsupported(E, "bitfield initialization");
454       return;
455     }
456     llvm::APInt V = CI->getValue();
457 
458     // Calculate information about the relevant field
459     const llvm::Type* Ty = CI->getType();
460     const llvm::TargetData &TD = CGM.getTypes().getTargetData();
461     unsigned size = TD.getTypeAllocSizeInBits(Ty);
462     CodeGenTypes::BitFieldInfo Info = CGM.getTypes().getBitFieldInfo(Field);
463     unsigned FieldOffset = Info.FieldNo * size;
464 
465     FieldOffset += Info.Start;
466 
467     // Find where to start the insertion
468     // FIXME: This is O(n^2) in the number of bit-fields!
469     // FIXME: This won't work if the struct isn't completely packed!
470     unsigned offset = 0, i = 0;
471     while (offset < (FieldOffset & -8))
472       offset += TD.getTypeAllocSizeInBits(Elts[i++]->getType());
473 
474     // Advance over 0 sized elements (must terminate in bounds since
475     // the bitfield must have a size).
476     while (TD.getTypeAllocSizeInBits(Elts[i]->getType()) == 0)
477       ++i;
478 
479     // Promote the size of V if necessary
480     // FIXME: This should never occur, but currently it can because initializer
481     // constants are cast to bool, and because clang is not enforcing bitfield
482     // width limits.
483     if (Info.Size > V.getBitWidth())
484       V.zext(Info.Size);
485 
486     // Insert the bits into the struct
487     // FIXME: This algorthm is only correct on X86!
488     // FIXME: THis algorthm assumes bit-fields only have byte-size elements!
489     unsigned bitsToInsert = Info.Size;
490     unsigned curBits = std::min(8 - (FieldOffset & 7), bitsToInsert);
491     unsigned byte = V.getLoBits(curBits).getZExtValue() << (FieldOffset & 7);
492     do {
493       llvm::Constant* byteC =
494         llvm::ConstantInt::get(llvm::Type::Int8Ty, byte);
495       Elts[i] = llvm::ConstantExpr::getOr(Elts[i], byteC);
496       ++i;
497       V = V.lshr(curBits);
498       bitsToInsert -= curBits;
499 
500       if (!bitsToInsert)
501         break;
502 
503       curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
504       byte = V.getLoBits(curBits).getZExtValue();
505     } while (true);
506   }
507 
508   llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
509     return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
510 
511     // FIXME: Remove the old struct builder once we're sure that the new one
512     // works well enough!
513     const llvm::StructType *SType =
514         cast<llvm::StructType>(ConvertType(ILE->getType()));
515     RecordDecl *RD = ILE->getType()->getAs<RecordType>()->getDecl();
516     std::vector<llvm::Constant*> Elts;
517 
518     // Initialize the whole structure to zero.
519     // FIXME: This doesn't handle member pointers correctly!
520     for (unsigned i = 0; i < SType->getNumElements(); ++i) {
521       const llvm::Type *FieldTy = SType->getElementType(i);
522       Elts.push_back(llvm::Constant::getNullValue(FieldTy));
523     }
524 
525     // Copy initializer elements. Skip padding fields.
526     unsigned EltNo = 0;  // Element no in ILE
527     bool RewriteType = false;
528     for (RecordDecl::field_iterator Field = RD->field_begin(),
529                                  FieldEnd = RD->field_end();
530          EltNo < ILE->getNumInits() && Field != FieldEnd; ++Field) {
531       if (Field->isBitField()) {
532         if (!Field->getIdentifier())
533           continue;
534         InsertBitfieldIntoStruct(Elts, *Field, ILE->getInit(EltNo));
535       } else {
536         unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(*Field);
537         llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(EltNo),
538                                                  Field->getType(), CGF);
539         if (!C) return 0;
540         RewriteType |= (C->getType() != Elts[FieldNo]->getType());
541         Elts[FieldNo] = C;
542       }
543       EltNo++;
544     }
545 
546     if (RewriteType) {
547       // FIXME: Make this work for non-packed structs
548       assert(SType->isPacked() && "Cannot recreate unpacked structs");
549       std::vector<const llvm::Type*> Types;
550       for (unsigned i = 0; i < Elts.size(); ++i)
551         Types.push_back(Elts[i]->getType());
552       SType = llvm::StructType::get(Types, true);
553     }
554 
555     return llvm::ConstantStruct::get(SType, Elts);
556   }
557 
558   llvm::Constant *EmitUnion(llvm::Constant *C, const llvm::Type *Ty) {
559     if (!C)
560       return 0;
561 
562     // Build a struct with the union sub-element as the first member,
563     // and padded to the appropriate size
564     std::vector<llvm::Constant*> Elts;
565     std::vector<const llvm::Type*> Types;
566     Elts.push_back(C);
567     Types.push_back(C->getType());
568     unsigned CurSize = CGM.getTargetData().getTypeAllocSize(C->getType());
569     unsigned TotalSize = CGM.getTargetData().getTypeAllocSize(Ty);
570 
571     assert(CurSize <= TotalSize && "Union size mismatch!");
572     if (unsigned NumPadBytes = TotalSize - CurSize) {
573       const llvm::Type *Ty = llvm::Type::Int8Ty;
574       if (NumPadBytes > 1)
575         Ty = llvm::ArrayType::get(Ty, NumPadBytes);
576 
577       Elts.push_back(llvm::Constant::getNullValue(Ty));
578       Types.push_back(Ty);
579     }
580 
581     llvm::StructType* STy = llvm::StructType::get(Types, false);
582     return llvm::ConstantStruct::get(STy, Elts);
583   }
584 
585   llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
586     const llvm::Type *Ty = ConvertType(ILE->getType());
587 
588     FieldDecl* curField = ILE->getInitializedFieldInUnion();
589     if (!curField) {
590       // There's no field to initialize, so value-initialize the union.
591 #ifndef NDEBUG
592       // Make sure that it's really an empty and not a failure of
593       // semantic analysis.
594       RecordDecl *RD = ILE->getType()->getAs<RecordType>()->getDecl();
595       for (RecordDecl::field_iterator Field = RD->field_begin(),
596                                    FieldEnd = RD->field_end();
597            Field != FieldEnd; ++Field)
598         assert(Field->isUnnamedBitfield() && "Only unnamed bitfields allowed");
599 #endif
600       return llvm::Constant::getNullValue(Ty);
601     }
602 
603     if (curField->isBitField()) {
604       // Create a dummy struct for bit-field insertion
605       unsigned NumElts = CGM.getTargetData().getTypeAllocSize(Ty);
606       llvm::Constant* NV =
607         llvm::Constant::getNullValue(llvm::Type::Int8Ty);
608       std::vector<llvm::Constant*> Elts(NumElts, NV);
609 
610       InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
611       const llvm::ArrayType *RetTy =
612           llvm::ArrayType::get(NV->getType(), NumElts);
613       return llvm::ConstantArray::get(RetTy, Elts);
614     }
615 
616     llvm::Constant *InitElem;
617     if (ILE->getNumInits() > 0) {
618       Expr *Init = ILE->getInit(0);
619       InitElem = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
620     } else {
621       InitElem = CGM.EmitNullConstant(curField->getType());
622     }
623     return EmitUnion(InitElem, Ty);
624   }
625 
626   llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
627     const llvm::VectorType *VType =
628         cast<llvm::VectorType>(ConvertType(ILE->getType()));
629     const llvm::Type *ElemTy = VType->getElementType();
630     std::vector<llvm::Constant*> Elts;
631     unsigned NumElements = VType->getNumElements();
632     unsigned NumInitElements = ILE->getNumInits();
633 
634     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
635 
636     // Copy initializer elements.
637     unsigned i = 0;
638     for (; i < NumInitableElts; ++i) {
639       Expr *Init = ILE->getInit(i);
640       llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
641       if (!C)
642         return 0;
643       Elts.push_back(C);
644     }
645 
646     for (; i < NumElements; ++i)
647       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
648 
649     return llvm::ConstantVector::get(VType, Elts);
650   }
651 
652   llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
653     return CGM.EmitNullConstant(E->getType());
654   }
655 
656   llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
657     if (ILE->getType()->isScalarType()) {
658       // We have a scalar in braces. Just use the first element.
659       if (ILE->getNumInits() > 0) {
660         Expr *Init = ILE->getInit(0);
661         return CGM.EmitConstantExpr(Init, Init->getType(), CGF);
662       }
663       return CGM.EmitNullConstant(ILE->getType());
664     }
665 
666     if (ILE->getType()->isArrayType())
667       return EmitArrayInitialization(ILE);
668 
669     if (ILE->getType()->isStructureType())
670       return EmitStructInitialization(ILE);
671 
672     if (ILE->getType()->isUnionType())
673       return EmitUnionInitialization(ILE);
674 
675     if (ILE->getType()->isVectorType())
676       return EmitVectorInitialization(ILE);
677 
678     assert(0 && "Unable to handle InitListExpr");
679     // Get rid of control reaches end of void function warning.
680     // Not reached.
681     return 0;
682   }
683 
684   llvm::Constant *VisitStringLiteral(StringLiteral *E) {
685     assert(!E->getType()->isPointerType() && "Strings are always arrays");
686 
687     // This must be a string initializing an array in a static initializer.
688     // Don't emit it as the address of the string, emit the string data itself
689     // as an inline array.
690     return llvm::ConstantArray::get(CGM.GetStringForStringLiteral(E), false);
691   }
692 
693   llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
694     // This must be an @encode initializing an array in a static initializer.
695     // Don't emit it as the address of the string, emit the string data itself
696     // as an inline array.
697     std::string Str;
698     CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
699     const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
700 
701     // Resize the string to the right size, adding zeros at the end, or
702     // truncating as needed.
703     Str.resize(CAT->getSize().getZExtValue(), '\0');
704     return llvm::ConstantArray::get(Str, false);
705   }
706 
707   llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
708     return Visit(E->getSubExpr());
709   }
710 
711   // Utility methods
712   const llvm::Type *ConvertType(QualType T) {
713     return CGM.getTypes().ConvertType(T);
714   }
715 
716 public:
717   llvm::Constant *EmitLValue(Expr *E) {
718     switch (E->getStmtClass()) {
719     default: break;
720     case Expr::CompoundLiteralExprClass: {
721       // Note that due to the nature of compound literals, this is guaranteed
722       // to be the only use of the variable, so we just generate it here.
723       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
724       llvm::Constant* C = Visit(CLE->getInitializer());
725       // FIXME: "Leaked" on failure.
726       if (C)
727         C = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
728                                      E->getType().isConstQualified(),
729                                      llvm::GlobalValue::InternalLinkage,
730                                      C, ".compoundliteral");
731       return C;
732     }
733     case Expr::DeclRefExprClass:
734     case Expr::QualifiedDeclRefExprClass: {
735       NamedDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
736       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
737         return CGM.GetAddrOfFunction(GlobalDecl(FD));
738       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
739         // We can never refer to a variable with local storage.
740         if (!VD->hasLocalStorage()) {
741           if (VD->isFileVarDecl() || VD->hasExternalStorage())
742             return CGM.GetAddrOfGlobalVar(VD);
743           else if (VD->isBlockVarDecl()) {
744             assert(CGF && "Can't access static local vars without CGF");
745             return CGF->GetAddrOfStaticLocalVar(VD);
746           }
747         }
748       }
749       break;
750     }
751     case Expr::StringLiteralClass:
752       return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
753     case Expr::ObjCEncodeExprClass:
754       return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
755     case Expr::ObjCStringLiteralClass: {
756       ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
757       llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(SL);
758       return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
759     }
760     case Expr::PredefinedExprClass: {
761       // __func__/__FUNCTION__ -> "".  __PRETTY_FUNCTION__ -> "top level".
762       std::string Str;
763       if (cast<PredefinedExpr>(E)->getIdentType() ==
764           PredefinedExpr::PrettyFunction)
765         Str = "top level";
766 
767       return CGM.GetAddrOfConstantCString(Str, ".tmp");
768     }
769     case Expr::AddrLabelExprClass: {
770       assert(CGF && "Invalid address of label expression outside function.");
771       unsigned id = CGF->GetIDForAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
772       llvm::Constant *C = llvm::ConstantInt::get(llvm::Type::Int32Ty, id);
773       return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
774     }
775     case Expr::CallExprClass: {
776       CallExpr* CE = cast<CallExpr>(E);
777       if (CE->isBuiltinCall(CGM.getContext()) !=
778             Builtin::BI__builtin___CFStringMakeConstantString)
779         break;
780       const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
781       const StringLiteral *Literal = cast<StringLiteral>(Arg);
782       // FIXME: need to deal with UCN conversion issues.
783       return CGM.GetAddrOfConstantCFString(Literal);
784     }
785     case Expr::BlockExprClass: {
786       std::string FunctionName;
787       if (CGF)
788         FunctionName = CGF->CurFn->getName();
789       else
790         FunctionName = "global";
791 
792       return CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
793     }
794     }
795 
796     return 0;
797   }
798 };
799 
800 }  // end anonymous namespace.
801 
802 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
803                                                 QualType DestType,
804                                                 CodeGenFunction *CGF) {
805   Expr::EvalResult Result;
806 
807   bool Success = false;
808 
809   if (DestType->isReferenceType())
810     Success = E->EvaluateAsLValue(Result, Context);
811   else
812     Success = E->Evaluate(Result, Context);
813 
814   if (Success) {
815     assert(!Result.HasSideEffects &&
816            "Constant expr should not have any side effects!");
817     switch (Result.Val.getKind()) {
818     case APValue::Uninitialized:
819       assert(0 && "Constant expressions should be initialized.");
820       return 0;
821     case APValue::LValue: {
822       const llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
823       llvm::Constant *Offset =
824         llvm::ConstantInt::get(llvm::Type::Int64Ty,
825                                Result.Val.getLValueOffset());
826 
827       llvm::Constant *C;
828       if (const Expr *LVBase = Result.Val.getLValueBase()) {
829         C = ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
830 
831         // Apply offset if necessary.
832         if (!Offset->isNullValue()) {
833           const llvm::Type *Type =
834             llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
835           llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
836           Casted = llvm::ConstantExpr::getGetElementPtr(Casted, &Offset, 1);
837           C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
838         }
839 
840         // Convert to the appropriate type; this could be an lvalue for
841         // an integer.
842         if (isa<llvm::PointerType>(DestTy))
843           return llvm::ConstantExpr::getBitCast(C, DestTy);
844 
845         return llvm::ConstantExpr::getPtrToInt(C, DestTy);
846       } else {
847         C = Offset;
848 
849         // Convert to the appropriate type; this could be an lvalue for
850         // an integer.
851         if (isa<llvm::PointerType>(DestTy))
852           return llvm::ConstantExpr::getIntToPtr(C, DestTy);
853 
854         // If the types don't match this should only be a truncate.
855         if (C->getType() != DestTy)
856           return llvm::ConstantExpr::getTrunc(C, DestTy);
857 
858         return C;
859       }
860     }
861     case APValue::Int: {
862       llvm::Constant *C = llvm::ConstantInt::get(VMContext,
863                                                  Result.Val.getInt());
864 
865       if (C->getType() == llvm::Type::Int1Ty) {
866         const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
867         C = llvm::ConstantExpr::getZExt(C, BoolTy);
868       }
869       return C;
870     }
871     case APValue::ComplexInt: {
872       llvm::Constant *Complex[2];
873 
874       Complex[0] = llvm::ConstantInt::get(VMContext,
875                                           Result.Val.getComplexIntReal());
876       Complex[1] = llvm::ConstantInt::get(VMContext,
877                                           Result.Val.getComplexIntImag());
878 
879       return llvm::ConstantStruct::get(Complex, 2);
880     }
881     case APValue::Float:
882       return llvm::ConstantFP::get(VMContext, Result.Val.getFloat());
883     case APValue::ComplexFloat: {
884       llvm::Constant *Complex[2];
885 
886       Complex[0] = llvm::ConstantFP::get(VMContext,
887                                          Result.Val.getComplexFloatReal());
888       Complex[1] = llvm::ConstantFP::get(VMContext,
889                                          Result.Val.getComplexFloatImag());
890 
891       return llvm::ConstantStruct::get(Complex, 2);
892     }
893     case APValue::Vector: {
894       llvm::SmallVector<llvm::Constant *, 4> Inits;
895       unsigned NumElts = Result.Val.getVectorLength();
896 
897       for (unsigned i = 0; i != NumElts; ++i) {
898         APValue &Elt = Result.Val.getVectorElt(i);
899         if (Elt.isInt())
900           Inits.push_back(llvm::ConstantInt::get(VMContext, Elt.getInt()));
901         else
902           Inits.push_back(llvm::ConstantFP::get(VMContext, Elt.getFloat()));
903       }
904       return llvm::ConstantVector::get(&Inits[0], Inits.size());
905     }
906     }
907   }
908 
909   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
910   if (C && C->getType() == llvm::Type::Int1Ty) {
911     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
912     C = llvm::ConstantExpr::getZExt(C, BoolTy);
913   }
914   return C;
915 }
916 
917 llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
918   // Always return an LLVM null constant for now; this will change when we
919   // get support for IRGen of member pointers.
920   return llvm::Constant::getNullValue(getTypes().ConvertType(T));
921 }
922