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::getInt8Ty(CGF->getLLVMContext());
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::getInt8Ty(CGM.getLLVMContext());
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::getInt8Ty(VMContext);
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(VMContext,
549                                     CGM.GetStringForStringLiteral(E), false);
550   }
551 
552   llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
553     // This must be an @encode initializing an array in a static initializer.
554     // Don't emit it as the address of the string, emit the string data itself
555     // as an inline array.
556     std::string Str;
557     CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
558     const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
559 
560     // Resize the string to the right size, adding zeros at the end, or
561     // truncating as needed.
562     Str.resize(CAT->getSize().getZExtValue(), '\0');
563     return llvm::ConstantArray::get(VMContext, Str, false);
564   }
565 
566   llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
567     return Visit(E->getSubExpr());
568   }
569 
570   // Utility methods
571   const llvm::Type *ConvertType(QualType T) {
572     return CGM.getTypes().ConvertType(T);
573   }
574 
575 public:
576   llvm::Constant *EmitLValue(Expr *E) {
577     switch (E->getStmtClass()) {
578     default: break;
579     case Expr::CompoundLiteralExprClass: {
580       // Note that due to the nature of compound literals, this is guaranteed
581       // to be the only use of the variable, so we just generate it here.
582       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
583       llvm::Constant* C = Visit(CLE->getInitializer());
584       // FIXME: "Leaked" on failure.
585       if (C)
586         C = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
587                                      E->getType().isConstQualified(),
588                                      llvm::GlobalValue::InternalLinkage,
589                                      C, ".compoundliteral");
590       return C;
591     }
592     case Expr::DeclRefExprClass:
593     case Expr::QualifiedDeclRefExprClass: {
594       NamedDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
595       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
596         return CGM.GetAddrOfFunction(GlobalDecl(FD));
597       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
598         // We can never refer to a variable with local storage.
599         if (!VD->hasLocalStorage()) {
600           if (VD->isFileVarDecl() || VD->hasExternalStorage())
601             return CGM.GetAddrOfGlobalVar(VD);
602           else if (VD->isBlockVarDecl()) {
603             assert(CGF && "Can't access static local vars without CGF");
604             return CGF->GetAddrOfStaticLocalVar(VD);
605           }
606         }
607       }
608       break;
609     }
610     case Expr::StringLiteralClass:
611       return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
612     case Expr::ObjCEncodeExprClass:
613       return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
614     case Expr::ObjCStringLiteralClass: {
615       ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
616       llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(SL);
617       return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
618     }
619     case Expr::PredefinedExprClass: {
620       // __func__/__FUNCTION__ -> "".  __PRETTY_FUNCTION__ -> "top level".
621       std::string Str;
622       if (cast<PredefinedExpr>(E)->getIdentType() ==
623           PredefinedExpr::PrettyFunction)
624         Str = "top level";
625 
626       return CGM.GetAddrOfConstantCString(Str, ".tmp");
627     }
628     case Expr::AddrLabelExprClass: {
629       assert(CGF && "Invalid address of label expression outside function.");
630       unsigned id =
631           CGF->GetIDForAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
632       llvm::Constant *C =
633             llvm::ConstantInt::get(llvm::Type::getInt32Ty(VMContext), id);
634       return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
635     }
636     case Expr::CallExprClass: {
637       CallExpr* CE = cast<CallExpr>(E);
638       if (CE->isBuiltinCall(CGM.getContext()) !=
639             Builtin::BI__builtin___CFStringMakeConstantString)
640         break;
641       const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
642       const StringLiteral *Literal = cast<StringLiteral>(Arg);
643       // FIXME: need to deal with UCN conversion issues.
644       return CGM.GetAddrOfConstantCFString(Literal);
645     }
646     case Expr::BlockExprClass: {
647       std::string FunctionName;
648       if (CGF)
649         FunctionName = CGF->CurFn->getName();
650       else
651         FunctionName = "global";
652 
653       return CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
654     }
655     }
656 
657     return 0;
658   }
659 };
660 
661 }  // end anonymous namespace.
662 
663 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
664                                                 QualType DestType,
665                                                 CodeGenFunction *CGF) {
666   Expr::EvalResult Result;
667 
668   bool Success = false;
669 
670   if (DestType->isReferenceType())
671     Success = E->EvaluateAsLValue(Result, Context);
672   else
673     Success = E->Evaluate(Result, Context);
674 
675   if (Success) {
676     assert(!Result.HasSideEffects &&
677            "Constant expr should not have any side effects!");
678     switch (Result.Val.getKind()) {
679     case APValue::Uninitialized:
680       assert(0 && "Constant expressions should be initialized.");
681       return 0;
682     case APValue::LValue: {
683       const llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
684       llvm::Constant *Offset =
685         llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext),
686                                Result.Val.getLValueOffset());
687 
688       llvm::Constant *C;
689       if (const Expr *LVBase = Result.Val.getLValueBase()) {
690         C = ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
691 
692         // Apply offset if necessary.
693         if (!Offset->isNullValue()) {
694           const llvm::Type *Type =
695             llvm::PointerType::getUnqual(llvm::Type::getInt8Ty(VMContext));
696           llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
697           Casted = llvm::ConstantExpr::getGetElementPtr(Casted, &Offset, 1);
698           C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
699         }
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::getBitCast(C, DestTy);
705 
706         return llvm::ConstantExpr::getPtrToInt(C, DestTy);
707       } else {
708         C = Offset;
709 
710         // Convert to the appropriate type; this could be an lvalue for
711         // an integer.
712         if (isa<llvm::PointerType>(DestTy))
713           return llvm::ConstantExpr::getIntToPtr(C, DestTy);
714 
715         // If the types don't match this should only be a truncate.
716         if (C->getType() != DestTy)
717           return llvm::ConstantExpr::getTrunc(C, DestTy);
718 
719         return C;
720       }
721     }
722     case APValue::Int: {
723       llvm::Constant *C = llvm::ConstantInt::get(VMContext,
724                                                  Result.Val.getInt());
725 
726       if (C->getType() == llvm::Type::getInt1Ty(VMContext)) {
727         const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
728         C = llvm::ConstantExpr::getZExt(C, BoolTy);
729       }
730       return C;
731     }
732     case APValue::ComplexInt: {
733       llvm::Constant *Complex[2];
734 
735       Complex[0] = llvm::ConstantInt::get(VMContext,
736                                           Result.Val.getComplexIntReal());
737       Complex[1] = llvm::ConstantInt::get(VMContext,
738                                           Result.Val.getComplexIntImag());
739 
740       return llvm::ConstantStruct::get(VMContext, Complex, 2);
741     }
742     case APValue::Float:
743       return llvm::ConstantFP::get(VMContext, Result.Val.getFloat());
744     case APValue::ComplexFloat: {
745       llvm::Constant *Complex[2];
746 
747       Complex[0] = llvm::ConstantFP::get(VMContext,
748                                          Result.Val.getComplexFloatReal());
749       Complex[1] = llvm::ConstantFP::get(VMContext,
750                                          Result.Val.getComplexFloatImag());
751 
752       return llvm::ConstantStruct::get(VMContext, Complex, 2);
753     }
754     case APValue::Vector: {
755       llvm::SmallVector<llvm::Constant *, 4> Inits;
756       unsigned NumElts = Result.Val.getVectorLength();
757 
758       for (unsigned i = 0; i != NumElts; ++i) {
759         APValue &Elt = Result.Val.getVectorElt(i);
760         if (Elt.isInt())
761           Inits.push_back(llvm::ConstantInt::get(VMContext, Elt.getInt()));
762         else
763           Inits.push_back(llvm::ConstantFP::get(VMContext, Elt.getFloat()));
764       }
765       return llvm::ConstantVector::get(&Inits[0], Inits.size());
766     }
767     }
768   }
769 
770   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
771   if (C && C->getType() == llvm::Type::getInt1Ty(VMContext)) {
772     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
773     C = llvm::ConstantExpr::getZExt(C, BoolTy);
774   }
775   return C;
776 }
777 
778 llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
779   if (const ConstantArrayType *CAT = Context.getAsConstantArrayType(T)) {
780 
781     QualType ElementTy = CAT->getElementType();
782 
783     // FIXME: Handle arrays of structs that contain member pointers.
784     if (Context.getBaseElementType(ElementTy)->isMemberPointerType()) {
785       llvm::Constant *Element = EmitNullConstant(ElementTy);
786       uint64_t NumElements = CAT->getSize().getZExtValue();
787       std::vector<llvm::Constant *> Array(NumElements);
788       for (uint64_t i = 0; i != NumElements; ++i)
789         Array[i] = Element;
790 
791       const llvm::ArrayType *ATy =
792         cast<llvm::ArrayType>(getTypes().ConvertTypeForMem(T));
793       return llvm::ConstantArray::get(ATy, Array);
794     }
795   }
796 
797   // FIXME: Handle structs that contain member pointers.
798   if (T->isMemberPointerType())
799     return llvm::Constant::getAllOnesValue(getTypes().ConvertTypeForMem(T));
800 
801   return llvm::Constant::getNullValue(getTypes().ConvertTypeForMem(T));
802 }
803