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 
382       llvm::Constant *C =
383         CGM.EmitConstantExpr(SubExpr, SubExpr->getType(), CGF);
384       if (!C)
385         return 0;
386 
387       // Build a struct with the union sub-element as the first member,
388       // and padded to the appropriate size
389       std::vector<llvm::Constant*> Elts;
390       std::vector<const llvm::Type*> Types;
391       Elts.push_back(C);
392       Types.push_back(C->getType());
393       unsigned CurSize = CGM.getTargetData().getTypeAllocSize(C->getType());
394       unsigned TotalSize = CGM.getTargetData().getTypeAllocSize(Ty);
395 
396       assert(CurSize <= TotalSize && "Union size mismatch!");
397       if (unsigned NumPadBytes = TotalSize - CurSize) {
398         const llvm::Type *Ty = llvm::Type::Int8Ty;
399         if (NumPadBytes > 1)
400           Ty = llvm::ArrayType::get(Ty, NumPadBytes);
401 
402         Elts.push_back(llvm::Constant::getNullValue(Ty));
403         Types.push_back(Ty);
404       }
405 
406       llvm::StructType* STy = llvm::StructType::get(Types, false);
407       return llvm::ConstantStruct::get(STy, Elts);
408     }
409 
410     // Explicit and implicit no-op casts
411     QualType Ty = E->getType(), SubTy = E->getSubExpr()->getType();
412     if (CGM.getContext().hasSameUnqualifiedType(Ty, SubTy)) {
413       return Visit(E->getSubExpr());
414     }
415     return 0;
416   }
417 
418   llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
419     return Visit(DAE->getExpr());
420   }
421 
422   llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
423     std::vector<llvm::Constant*> Elts;
424     const llvm::ArrayType *AType =
425         cast<llvm::ArrayType>(ConvertType(ILE->getType()));
426     unsigned NumInitElements = ILE->getNumInits();
427     // FIXME: Check for wide strings
428     // FIXME: Check for NumInitElements exactly equal to 1??
429     if (NumInitElements > 0 &&
430         (isa<StringLiteral>(ILE->getInit(0)) ||
431          isa<ObjCEncodeExpr>(ILE->getInit(0))) &&
432         ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
433       return Visit(ILE->getInit(0));
434     const llvm::Type *ElemTy = AType->getElementType();
435     unsigned NumElements = AType->getNumElements();
436 
437     // Initialising an array requires us to automatically
438     // initialise any elements that have not been initialised explicitly
439     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
440 
441     // Copy initializer elements.
442     unsigned i = 0;
443     bool RewriteType = false;
444     for (; i < NumInitableElts; ++i) {
445       Expr *Init = ILE->getInit(i);
446       llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
447       if (!C)
448         return 0;
449       RewriteType |= (C->getType() != ElemTy);
450       Elts.push_back(C);
451     }
452 
453     // Initialize remaining array elements.
454     // FIXME: This doesn't handle member pointers correctly!
455     for (; i < NumElements; ++i)
456       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
457 
458     if (RewriteType) {
459       // FIXME: Try to avoid packing the array
460       std::vector<const llvm::Type*> Types;
461       for (unsigned i = 0; i < Elts.size(); ++i)
462         Types.push_back(Elts[i]->getType());
463       const llvm::StructType *SType = llvm::StructType::get(Types, true);
464       return llvm::ConstantStruct::get(SType, Elts);
465     }
466 
467     return llvm::ConstantArray::get(AType, Elts);
468   }
469 
470   llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
471     return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
472   }
473 
474   llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
475     return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
476   }
477 
478   llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
479     const llvm::VectorType *VType =
480         cast<llvm::VectorType>(ConvertType(ILE->getType()));
481     const llvm::Type *ElemTy = VType->getElementType();
482     std::vector<llvm::Constant*> Elts;
483     unsigned NumElements = VType->getNumElements();
484     unsigned NumInitElements = ILE->getNumInits();
485 
486     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
487 
488     // Copy initializer elements.
489     unsigned i = 0;
490     for (; i < NumInitableElts; ++i) {
491       Expr *Init = ILE->getInit(i);
492       llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
493       if (!C)
494         return 0;
495       Elts.push_back(C);
496     }
497 
498     for (; i < NumElements; ++i)
499       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
500 
501     return llvm::ConstantVector::get(VType, Elts);
502   }
503 
504   llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
505     return CGM.EmitNullConstant(E->getType());
506   }
507 
508   llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
509     if (ILE->getType()->isScalarType()) {
510       // We have a scalar in braces. Just use the first element.
511       if (ILE->getNumInits() > 0) {
512         Expr *Init = ILE->getInit(0);
513         return CGM.EmitConstantExpr(Init, Init->getType(), CGF);
514       }
515       return CGM.EmitNullConstant(ILE->getType());
516     }
517 
518     if (ILE->getType()->isArrayType())
519       return EmitArrayInitialization(ILE);
520 
521     if (ILE->getType()->isStructureType())
522       return EmitStructInitialization(ILE);
523 
524     if (ILE->getType()->isUnionType())
525       return EmitUnionInitialization(ILE);
526 
527     if (ILE->getType()->isVectorType())
528       return EmitVectorInitialization(ILE);
529 
530     assert(0 && "Unable to handle InitListExpr");
531     // Get rid of control reaches end of void function warning.
532     // Not reached.
533     return 0;
534   }
535 
536   llvm::Constant *VisitStringLiteral(StringLiteral *E) {
537     assert(!E->getType()->isPointerType() && "Strings are always arrays");
538 
539     // This must be a string initializing an array in a static initializer.
540     // Don't emit it as the address of the string, emit the string data itself
541     // as an inline array.
542     return llvm::ConstantArray::get(CGM.GetStringForStringLiteral(E), false);
543   }
544 
545   llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
546     // This must be an @encode initializing an array in a static initializer.
547     // Don't emit it as the address of the string, emit the string data itself
548     // as an inline array.
549     std::string Str;
550     CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
551     const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
552 
553     // Resize the string to the right size, adding zeros at the end, or
554     // truncating as needed.
555     Str.resize(CAT->getSize().getZExtValue(), '\0');
556     return llvm::ConstantArray::get(Str, false);
557   }
558 
559   llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
560     return Visit(E->getSubExpr());
561   }
562 
563   // Utility methods
564   const llvm::Type *ConvertType(QualType T) {
565     return CGM.getTypes().ConvertType(T);
566   }
567 
568 public:
569   llvm::Constant *EmitLValue(Expr *E) {
570     switch (E->getStmtClass()) {
571     default: break;
572     case Expr::CompoundLiteralExprClass: {
573       // Note that due to the nature of compound literals, this is guaranteed
574       // to be the only use of the variable, so we just generate it here.
575       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
576       llvm::Constant* C = Visit(CLE->getInitializer());
577       // FIXME: "Leaked" on failure.
578       if (C)
579         C = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
580                                      E->getType().isConstQualified(),
581                                      llvm::GlobalValue::InternalLinkage,
582                                      C, ".compoundliteral");
583       return C;
584     }
585     case Expr::DeclRefExprClass:
586     case Expr::QualifiedDeclRefExprClass: {
587       NamedDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
588       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
589         return CGM.GetAddrOfFunction(GlobalDecl(FD));
590       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
591         // We can never refer to a variable with local storage.
592         if (!VD->hasLocalStorage()) {
593           if (VD->isFileVarDecl() || VD->hasExternalStorage())
594             return CGM.GetAddrOfGlobalVar(VD);
595           else if (VD->isBlockVarDecl()) {
596             assert(CGF && "Can't access static local vars without CGF");
597             return CGF->GetAddrOfStaticLocalVar(VD);
598           }
599         }
600       }
601       break;
602     }
603     case Expr::StringLiteralClass:
604       return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
605     case Expr::ObjCEncodeExprClass:
606       return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
607     case Expr::ObjCStringLiteralClass: {
608       ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
609       llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(SL);
610       return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
611     }
612     case Expr::PredefinedExprClass: {
613       // __func__/__FUNCTION__ -> "".  __PRETTY_FUNCTION__ -> "top level".
614       std::string Str;
615       if (cast<PredefinedExpr>(E)->getIdentType() ==
616           PredefinedExpr::PrettyFunction)
617         Str = "top level";
618 
619       return CGM.GetAddrOfConstantCString(Str, ".tmp");
620     }
621     case Expr::AddrLabelExprClass: {
622       assert(CGF && "Invalid address of label expression outside function.");
623       unsigned id = CGF->GetIDForAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
624       llvm::Constant *C = llvm::ConstantInt::get(llvm::Type::Int32Ty, id);
625       return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
626     }
627     case Expr::CallExprClass: {
628       CallExpr* CE = cast<CallExpr>(E);
629       if (CE->isBuiltinCall(CGM.getContext()) !=
630             Builtin::BI__builtin___CFStringMakeConstantString)
631         break;
632       const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
633       const StringLiteral *Literal = cast<StringLiteral>(Arg);
634       // FIXME: need to deal with UCN conversion issues.
635       return CGM.GetAddrOfConstantCFString(Literal);
636     }
637     case Expr::BlockExprClass: {
638       std::string FunctionName;
639       if (CGF)
640         FunctionName = CGF->CurFn->getName();
641       else
642         FunctionName = "global";
643 
644       return CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
645     }
646     }
647 
648     return 0;
649   }
650 };
651 
652 }  // end anonymous namespace.
653 
654 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
655                                                 QualType DestType,
656                                                 CodeGenFunction *CGF) {
657   Expr::EvalResult Result;
658 
659   bool Success = false;
660 
661   if (DestType->isReferenceType())
662     Success = E->EvaluateAsLValue(Result, Context);
663   else
664     Success = E->Evaluate(Result, Context);
665 
666   if (Success) {
667     assert(!Result.HasSideEffects &&
668            "Constant expr should not have any side effects!");
669     switch (Result.Val.getKind()) {
670     case APValue::Uninitialized:
671       assert(0 && "Constant expressions should be initialized.");
672       return 0;
673     case APValue::LValue: {
674       const llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
675       llvm::Constant *Offset =
676         llvm::ConstantInt::get(llvm::Type::Int64Ty,
677                                Result.Val.getLValueOffset());
678 
679       llvm::Constant *C;
680       if (const Expr *LVBase = Result.Val.getLValueBase()) {
681         C = ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
682 
683         // Apply offset if necessary.
684         if (!Offset->isNullValue()) {
685           const llvm::Type *Type =
686             llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
687           llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
688           Casted = llvm::ConstantExpr::getGetElementPtr(Casted, &Offset, 1);
689           C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
690         }
691 
692         // Convert to the appropriate type; this could be an lvalue for
693         // an integer.
694         if (isa<llvm::PointerType>(DestTy))
695           return llvm::ConstantExpr::getBitCast(C, DestTy);
696 
697         return llvm::ConstantExpr::getPtrToInt(C, DestTy);
698       } else {
699         C = Offset;
700 
701         // Convert to the appropriate type; this could be an lvalue for
702         // an integer.
703         if (isa<llvm::PointerType>(DestTy))
704           return llvm::ConstantExpr::getIntToPtr(C, DestTy);
705 
706         // If the types don't match this should only be a truncate.
707         if (C->getType() != DestTy)
708           return llvm::ConstantExpr::getTrunc(C, DestTy);
709 
710         return C;
711       }
712     }
713     case APValue::Int: {
714       llvm::Constant *C = llvm::ConstantInt::get(VMContext,
715                                                  Result.Val.getInt());
716 
717       if (C->getType() == llvm::Type::Int1Ty) {
718         const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
719         C = llvm::ConstantExpr::getZExt(C, BoolTy);
720       }
721       return C;
722     }
723     case APValue::ComplexInt: {
724       llvm::Constant *Complex[2];
725 
726       Complex[0] = llvm::ConstantInt::get(VMContext,
727                                           Result.Val.getComplexIntReal());
728       Complex[1] = llvm::ConstantInt::get(VMContext,
729                                           Result.Val.getComplexIntImag());
730 
731       return llvm::ConstantStruct::get(Complex, 2);
732     }
733     case APValue::Float:
734       return llvm::ConstantFP::get(VMContext, Result.Val.getFloat());
735     case APValue::ComplexFloat: {
736       llvm::Constant *Complex[2];
737 
738       Complex[0] = llvm::ConstantFP::get(VMContext,
739                                          Result.Val.getComplexFloatReal());
740       Complex[1] = llvm::ConstantFP::get(VMContext,
741                                          Result.Val.getComplexFloatImag());
742 
743       return llvm::ConstantStruct::get(Complex, 2);
744     }
745     case APValue::Vector: {
746       llvm::SmallVector<llvm::Constant *, 4> Inits;
747       unsigned NumElts = Result.Val.getVectorLength();
748 
749       for (unsigned i = 0; i != NumElts; ++i) {
750         APValue &Elt = Result.Val.getVectorElt(i);
751         if (Elt.isInt())
752           Inits.push_back(llvm::ConstantInt::get(VMContext, Elt.getInt()));
753         else
754           Inits.push_back(llvm::ConstantFP::get(VMContext, Elt.getFloat()));
755       }
756       return llvm::ConstantVector::get(&Inits[0], Inits.size());
757     }
758     }
759   }
760 
761   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
762   if (C && C->getType() == llvm::Type::Int1Ty) {
763     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
764     C = llvm::ConstantExpr::getZExt(C, BoolTy);
765   }
766   return C;
767 }
768 
769 llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
770   // Always return an LLVM null constant for now; this will change when we
771   // get support for IRGen of member pointers.
772   return llvm::Constant::getNullValue(getTypes().ConvertType(T));
773 }
774