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(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 (RD->isUnion() && ILE->getInitializedFieldInUnion() != *Field)
284         continue;
285 
286       if (Field->isBitField()) {
287         if (!Field->getIdentifier())
288           continue;
289 
290         if (!AppendBitField(*Field, Layout.getFieldOffset(FieldNo),
291                             ILE->getInit(ElementNo)))
292           return false;
293       } else {
294         if (!AppendField(*Field, Layout.getFieldOffset(FieldNo),
295                          ILE->getInit(ElementNo)))
296           return false;
297       }
298 
299       ElementNo++;
300     }
301 
302     uint64_t LayoutSizeInBytes = Layout.getSize() / 8;
303 
304     if (NextFieldOffsetInBytes > LayoutSizeInBytes) {
305       // If the struct is bigger than the size of the record type,
306       // we must have a flexible array member at the end.
307       assert(RD->hasFlexibleArrayMember() &&
308              "Must have flexible array member if struct is bigger than type!");
309 
310       // No tail padding is necessary.
311       return true;
312     }
313 
314     // Append tail padding if necessary.
315     AppendTailPadding(Layout.getSize());
316 
317     assert(Layout.getSize() / 8 == NextFieldOffsetInBytes &&
318            "Tail padding mismatch!");
319 
320     return true;
321   }
322 
323   unsigned getAlignment(const llvm::Constant *C) const {
324     if (Packed)
325       return 1;
326 
327     return CGM.getTargetData().getABITypeAlignment(C->getType());
328   }
329 
330   uint64_t getSizeInBytes(const llvm::Constant *C) const {
331     return CGM.getTargetData().getTypeAllocSize(C->getType());
332   }
333 
334 public:
335   static llvm::Constant *BuildStruct(CodeGenModule &CGM, CodeGenFunction *CGF,
336                                      InitListExpr *ILE) {
337     ConstStructBuilder Builder(CGM, CGF);
338 
339     if (!Builder.Build(ILE))
340       return 0;
341 
342     llvm::Constant *Result =
343       llvm::ConstantStruct::get(CGM.getLLVMContext(),
344                                 Builder.Elements, Builder.Packed);
345 
346     assert(llvm::RoundUpToAlignment(Builder.NextFieldOffsetInBytes,
347                                     Builder.getAlignment(Result)) ==
348            Builder.getSizeInBytes(Result) && "Size mismatch!");
349 
350     return Result;
351   }
352 };
353 
354 class VISIBILITY_HIDDEN ConstExprEmitter :
355   public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
356   CodeGenModule &CGM;
357   CodeGenFunction *CGF;
358   llvm::LLVMContext &VMContext;
359 public:
360   ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
361     : CGM(cgm), CGF(cgf), VMContext(cgm.getLLVMContext()) {
362   }
363 
364   //===--------------------------------------------------------------------===//
365   //                            Visitor Methods
366   //===--------------------------------------------------------------------===//
367 
368   llvm::Constant *VisitStmt(Stmt *S) {
369     return 0;
370   }
371 
372   llvm::Constant *VisitParenExpr(ParenExpr *PE) {
373     return Visit(PE->getSubExpr());
374   }
375 
376   llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
377     return Visit(E->getInitializer());
378   }
379 
380   llvm::Constant *VisitCastExpr(CastExpr* E) {
381     // GCC cast to union extension
382     if (E->getType()->isUnionType()) {
383       const llvm::Type *Ty = ConvertType(E->getType());
384       Expr *SubExpr = E->getSubExpr();
385 
386       llvm::Constant *C =
387         CGM.EmitConstantExpr(SubExpr, SubExpr->getType(), CGF);
388       if (!C)
389         return 0;
390 
391       // Build a struct with the union sub-element as the first member,
392       // and padded to the appropriate size
393       std::vector<llvm::Constant*> Elts;
394       std::vector<const llvm::Type*> Types;
395       Elts.push_back(C);
396       Types.push_back(C->getType());
397       unsigned CurSize = CGM.getTargetData().getTypeAllocSize(C->getType());
398       unsigned TotalSize = CGM.getTargetData().getTypeAllocSize(Ty);
399 
400       assert(CurSize <= TotalSize && "Union size mismatch!");
401       if (unsigned NumPadBytes = TotalSize - CurSize) {
402         const llvm::Type *Ty = llvm::Type::Int8Ty;
403         if (NumPadBytes > 1)
404           Ty = llvm::ArrayType::get(Ty, NumPadBytes);
405 
406         Elts.push_back(llvm::Constant::getNullValue(Ty));
407         Types.push_back(Ty);
408       }
409 
410       llvm::StructType* STy = llvm::StructType::get(C->getType()->getContext(),
411                                                     Types, false);
412       return llvm::ConstantStruct::get(STy, Elts);
413     }
414 
415     // Explicit and implicit no-op casts
416     QualType Ty = E->getType(), SubTy = E->getSubExpr()->getType();
417     if (CGM.getContext().hasSameUnqualifiedType(Ty, SubTy)) {
418       return Visit(E->getSubExpr());
419     }
420     return 0;
421   }
422 
423   llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
424     return Visit(DAE->getExpr());
425   }
426 
427   llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
428     std::vector<llvm::Constant*> Elts;
429     const llvm::ArrayType *AType =
430         cast<llvm::ArrayType>(ConvertType(ILE->getType()));
431     unsigned NumInitElements = ILE->getNumInits();
432     // FIXME: Check for wide strings
433     // FIXME: Check for NumInitElements exactly equal to 1??
434     if (NumInitElements > 0 &&
435         (isa<StringLiteral>(ILE->getInit(0)) ||
436          isa<ObjCEncodeExpr>(ILE->getInit(0))) &&
437         ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
438       return Visit(ILE->getInit(0));
439     const llvm::Type *ElemTy = AType->getElementType();
440     unsigned NumElements = AType->getNumElements();
441 
442     // Initialising an array requires us to automatically
443     // initialise any elements that have not been initialised explicitly
444     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
445 
446     // Copy initializer elements.
447     unsigned i = 0;
448     bool RewriteType = false;
449     for (; i < NumInitableElts; ++i) {
450       Expr *Init = ILE->getInit(i);
451       llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
452       if (!C)
453         return 0;
454       RewriteType |= (C->getType() != ElemTy);
455       Elts.push_back(C);
456     }
457 
458     // Initialize remaining array elements.
459     // FIXME: This doesn't handle member pointers correctly!
460     for (; i < NumElements; ++i)
461       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
462 
463     if (RewriteType) {
464       // FIXME: Try to avoid packing the array
465       std::vector<const llvm::Type*> Types;
466       for (unsigned i = 0; i < Elts.size(); ++i)
467         Types.push_back(Elts[i]->getType());
468       const llvm::StructType *SType = llvm::StructType::get(AType->getContext(),
469                                                             Types, true);
470       return llvm::ConstantStruct::get(SType, Elts);
471     }
472 
473     return llvm::ConstantArray::get(AType, Elts);
474   }
475 
476   llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
477     return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
478   }
479 
480   llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
481     return ConstStructBuilder::BuildStruct(CGM, CGF, ILE);
482   }
483 
484   llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
485     const llvm::VectorType *VType =
486         cast<llvm::VectorType>(ConvertType(ILE->getType()));
487     const llvm::Type *ElemTy = VType->getElementType();
488     std::vector<llvm::Constant*> Elts;
489     unsigned NumElements = VType->getNumElements();
490     unsigned NumInitElements = ILE->getNumInits();
491 
492     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
493 
494     // Copy initializer elements.
495     unsigned i = 0;
496     for (; i < NumInitableElts; ++i) {
497       Expr *Init = ILE->getInit(i);
498       llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
499       if (!C)
500         return 0;
501       Elts.push_back(C);
502     }
503 
504     for (; i < NumElements; ++i)
505       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
506 
507     return llvm::ConstantVector::get(VType, Elts);
508   }
509 
510   llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
511     return CGM.EmitNullConstant(E->getType());
512   }
513 
514   llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
515     if (ILE->getType()->isScalarType()) {
516       // We have a scalar in braces. Just use the first element.
517       if (ILE->getNumInits() > 0) {
518         Expr *Init = ILE->getInit(0);
519         return CGM.EmitConstantExpr(Init, Init->getType(), CGF);
520       }
521       return CGM.EmitNullConstant(ILE->getType());
522     }
523 
524     if (ILE->getType()->isArrayType())
525       return EmitArrayInitialization(ILE);
526 
527     if (ILE->getType()->isStructureType())
528       return EmitStructInitialization(ILE);
529 
530     if (ILE->getType()->isUnionType())
531       return EmitUnionInitialization(ILE);
532 
533     if (ILE->getType()->isVectorType())
534       return EmitVectorInitialization(ILE);
535 
536     assert(0 && "Unable to handle InitListExpr");
537     // Get rid of control reaches end of void function warning.
538     // Not reached.
539     return 0;
540   }
541 
542   llvm::Constant *VisitStringLiteral(StringLiteral *E) {
543     assert(!E->getType()->isPointerType() && "Strings are always arrays");
544 
545     // This must be a string initializing an array in a static initializer.
546     // Don't emit it as the address of the string, emit the string data itself
547     // as an inline array.
548     return llvm::ConstantArray::get(CGM.GetStringForStringLiteral(E), false);
549   }
550 
551   llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
552     // This must be an @encode initializing an array in a static initializer.
553     // Don't emit it as the address of the string, emit the string data itself
554     // as an inline array.
555     std::string Str;
556     CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
557     const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
558 
559     // Resize the string to the right size, adding zeros at the end, or
560     // truncating as needed.
561     Str.resize(CAT->getSize().getZExtValue(), '\0');
562     return llvm::ConstantArray::get(Str, false);
563   }
564 
565   llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
566     return Visit(E->getSubExpr());
567   }
568 
569   // Utility methods
570   const llvm::Type *ConvertType(QualType T) {
571     return CGM.getTypes().ConvertType(T);
572   }
573 
574 public:
575   llvm::Constant *EmitLValue(Expr *E) {
576     switch (E->getStmtClass()) {
577     default: break;
578     case Expr::CompoundLiteralExprClass: {
579       // Note that due to the nature of compound literals, this is guaranteed
580       // to be the only use of the variable, so we just generate it here.
581       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
582       llvm::Constant* C = Visit(CLE->getInitializer());
583       // FIXME: "Leaked" on failure.
584       if (C)
585         C = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
586                                      E->getType().isConstQualified(),
587                                      llvm::GlobalValue::InternalLinkage,
588                                      C, ".compoundliteral");
589       return C;
590     }
591     case Expr::DeclRefExprClass:
592     case Expr::QualifiedDeclRefExprClass: {
593       NamedDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
594       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
595         return CGM.GetAddrOfFunction(GlobalDecl(FD));
596       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
597         // We can never refer to a variable with local storage.
598         if (!VD->hasLocalStorage()) {
599           if (VD->isFileVarDecl() || VD->hasExternalStorage())
600             return CGM.GetAddrOfGlobalVar(VD);
601           else if (VD->isBlockVarDecl()) {
602             assert(CGF && "Can't access static local vars without CGF");
603             return CGF->GetAddrOfStaticLocalVar(VD);
604           }
605         }
606       }
607       break;
608     }
609     case Expr::StringLiteralClass:
610       return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
611     case Expr::ObjCEncodeExprClass:
612       return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
613     case Expr::ObjCStringLiteralClass: {
614       ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
615       llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(SL);
616       return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
617     }
618     case Expr::PredefinedExprClass: {
619       // __func__/__FUNCTION__ -> "".  __PRETTY_FUNCTION__ -> "top level".
620       std::string Str;
621       if (cast<PredefinedExpr>(E)->getIdentType() ==
622           PredefinedExpr::PrettyFunction)
623         Str = "top level";
624 
625       return CGM.GetAddrOfConstantCString(Str, ".tmp");
626     }
627     case Expr::AddrLabelExprClass: {
628       assert(CGF && "Invalid address of label expression outside function.");
629       unsigned id = CGF->GetIDForAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
630       llvm::Constant *C = llvm::ConstantInt::get(llvm::Type::Int32Ty, id);
631       return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
632     }
633     case Expr::CallExprClass: {
634       CallExpr* CE = cast<CallExpr>(E);
635       if (CE->isBuiltinCall(CGM.getContext()) !=
636             Builtin::BI__builtin___CFStringMakeConstantString)
637         break;
638       const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
639       const StringLiteral *Literal = cast<StringLiteral>(Arg);
640       // FIXME: need to deal with UCN conversion issues.
641       return CGM.GetAddrOfConstantCFString(Literal);
642     }
643     case Expr::BlockExprClass: {
644       std::string FunctionName;
645       if (CGF)
646         FunctionName = CGF->CurFn->getName();
647       else
648         FunctionName = "global";
649 
650       return CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
651     }
652     }
653 
654     return 0;
655   }
656 };
657 
658 }  // end anonymous namespace.
659 
660 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
661                                                 QualType DestType,
662                                                 CodeGenFunction *CGF) {
663   Expr::EvalResult Result;
664 
665   bool Success = false;
666 
667   if (DestType->isReferenceType())
668     Success = E->EvaluateAsLValue(Result, Context);
669   else
670     Success = E->Evaluate(Result, Context);
671 
672   if (Success) {
673     assert(!Result.HasSideEffects &&
674            "Constant expr should not have any side effects!");
675     switch (Result.Val.getKind()) {
676     case APValue::Uninitialized:
677       assert(0 && "Constant expressions should be initialized.");
678       return 0;
679     case APValue::LValue: {
680       const llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
681       llvm::Constant *Offset =
682         llvm::ConstantInt::get(llvm::Type::Int64Ty,
683                                Result.Val.getLValueOffset());
684 
685       llvm::Constant *C;
686       if (const Expr *LVBase = Result.Val.getLValueBase()) {
687         C = ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
688 
689         // Apply offset if necessary.
690         if (!Offset->isNullValue()) {
691           const llvm::Type *Type =
692             llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
693           llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
694           Casted = llvm::ConstantExpr::getGetElementPtr(Casted, &Offset, 1);
695           C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
696         }
697 
698         // Convert to the appropriate type; this could be an lvalue for
699         // an integer.
700         if (isa<llvm::PointerType>(DestTy))
701           return llvm::ConstantExpr::getBitCast(C, DestTy);
702 
703         return llvm::ConstantExpr::getPtrToInt(C, DestTy);
704       } else {
705         C = Offset;
706 
707         // Convert to the appropriate type; this could be an lvalue for
708         // an integer.
709         if (isa<llvm::PointerType>(DestTy))
710           return llvm::ConstantExpr::getIntToPtr(C, DestTy);
711 
712         // If the types don't match this should only be a truncate.
713         if (C->getType() != DestTy)
714           return llvm::ConstantExpr::getTrunc(C, DestTy);
715 
716         return C;
717       }
718     }
719     case APValue::Int: {
720       llvm::Constant *C = llvm::ConstantInt::get(VMContext,
721                                                  Result.Val.getInt());
722 
723       if (C->getType() == llvm::Type::Int1Ty) {
724         const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
725         C = llvm::ConstantExpr::getZExt(C, BoolTy);
726       }
727       return C;
728     }
729     case APValue::ComplexInt: {
730       llvm::Constant *Complex[2];
731 
732       Complex[0] = llvm::ConstantInt::get(VMContext,
733                                           Result.Val.getComplexIntReal());
734       Complex[1] = llvm::ConstantInt::get(VMContext,
735                                           Result.Val.getComplexIntImag());
736 
737       return llvm::ConstantStruct::get(VMContext, Complex, 2);
738     }
739     case APValue::Float:
740       return llvm::ConstantFP::get(VMContext, Result.Val.getFloat());
741     case APValue::ComplexFloat: {
742       llvm::Constant *Complex[2];
743 
744       Complex[0] = llvm::ConstantFP::get(VMContext,
745                                          Result.Val.getComplexFloatReal());
746       Complex[1] = llvm::ConstantFP::get(VMContext,
747                                          Result.Val.getComplexFloatImag());
748 
749       return llvm::ConstantStruct::get(VMContext, Complex, 2);
750     }
751     case APValue::Vector: {
752       llvm::SmallVector<llvm::Constant *, 4> Inits;
753       unsigned NumElts = Result.Val.getVectorLength();
754 
755       for (unsigned i = 0; i != NumElts; ++i) {
756         APValue &Elt = Result.Val.getVectorElt(i);
757         if (Elt.isInt())
758           Inits.push_back(llvm::ConstantInt::get(VMContext, Elt.getInt()));
759         else
760           Inits.push_back(llvm::ConstantFP::get(VMContext, Elt.getFloat()));
761       }
762       return llvm::ConstantVector::get(&Inits[0], Inits.size());
763     }
764     }
765   }
766 
767   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
768   if (C && C->getType() == llvm::Type::Int1Ty) {
769     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
770     C = llvm::ConstantExpr::getZExt(C, BoolTy);
771   }
772   return C;
773 }
774 
775 llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
776   // Always return an LLVM null constant for now; this will change when we
777   // get support for IRGen of member pointers.
778   return llvm::Constant::getNullValue(getTypes().ConvertTypeForMem(T));
779 }
780