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 "clang/AST/AST.h"
17 #include "llvm/Constants.h"
18 #include "llvm/Function.h"
19 #include "llvm/GlobalVariable.h"
20 #include "llvm/Support/Compiler.h"
21 using namespace clang;
22 using namespace CodeGen;
23 
24 namespace  {
25 class VISIBILITY_HIDDEN ConstExprEmitter :
26   public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
27   CodeGenModule &CGM;
28   CodeGenFunction *CGF;
29 public:
30   ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
31     : CGM(cgm), CGF(cgf) {
32   }
33 
34   //===--------------------------------------------------------------------===//
35   //                            Visitor Methods
36   //===--------------------------------------------------------------------===//
37 
38   llvm::Constant *VisitStmt(Stmt *S) {
39     CGM.WarnUnsupported(S, "constant expression");
40     QualType T = cast<Expr>(S)->getType();
41     return llvm::UndefValue::get(CGM.getTypes().ConvertType(T));
42   }
43 
44   llvm::Constant *VisitParenExpr(ParenExpr *PE) {
45     return Visit(PE->getSubExpr());
46   }
47 
48   // Leaves
49   llvm::Constant *VisitIntegerLiteral(const IntegerLiteral *E) {
50     return llvm::ConstantInt::get(E->getValue());
51   }
52   llvm::Constant *VisitFloatingLiteral(const FloatingLiteral *E) {
53     return llvm::ConstantFP::get(E->getValue());
54   }
55   llvm::Constant *VisitCharacterLiteral(const CharacterLiteral *E) {
56     return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
57   }
58   llvm::Constant *VisitCXXBoolLiteralExpr(const CXXBoolLiteralExpr *E) {
59     return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
60   }
61 
62   llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
63     return Visit(E->getInitializer());
64   }
65 
66   llvm::Constant *VisitCastExpr(const CastExpr* E) {
67     llvm::Constant *C = Visit(E->getSubExpr());
68 
69     return EmitConversion(C, E->getSubExpr()->getType(), E->getType());
70   }
71 
72   llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
73     return Visit(DAE->getExpr());
74   }
75 
76   llvm::Constant *EmitArrayInitialization(InitListExpr *ILE,
77                                           const llvm::ArrayType *AType) {
78     std::vector<llvm::Constant*> Elts;
79     unsigned NumInitElements = ILE->getNumInits();
80     // FIXME: Check for wide strings
81     if (NumInitElements > 0 && isa<StringLiteral>(ILE->getInit(0)) &&
82         ILE->getType()->getAsArrayType()->getElementType()->isCharType())
83       return Visit(ILE->getInit(0));
84     const llvm::Type *ElemTy = AType->getElementType();
85     unsigned NumElements = AType->getNumElements();
86 
87     // Initialising an array requires us to automatically
88     // initialise any elements that have not been initialised explicitly
89     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
90 
91     // Copy initializer elements.
92     unsigned i = 0;
93     for (; i < NumInitableElts; ++i) {
94 
95       llvm::Constant *C = Visit(ILE->getInit(i));
96       // FIXME: Remove this when sema of initializers is finished (and the code
97       // above).
98       if (C == 0 && ILE->getInit(i)->getType()->isVoidType()) {
99         if (ILE->getType()->isVoidType()) return 0;
100         return llvm::UndefValue::get(AType);
101       }
102       assert (C && "Failed to create initializer expression");
103       Elts.push_back(C);
104     }
105 
106     // Initialize remaining array elements.
107     for (; i < NumElements; ++i)
108       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
109 
110     return llvm::ConstantArray::get(AType, Elts);
111   }
112 
113   llvm::Constant *EmitStructInitialization(InitListExpr *ILE,
114                                            const llvm::StructType *SType) {
115 
116     TagDecl *TD = ILE->getType()->getAsRecordType()->getDecl();
117     std::vector<llvm::Constant*> Elts;
118     const CGRecordLayout *CGR = CGM.getTypes().getCGRecordLayout(TD);
119     unsigned NumInitElements = ILE->getNumInits();
120     unsigned NumElements = SType->getNumElements();
121 
122     // Initialising an structure requires us to automatically
123     // initialise any elements that have not been initialised explicitly
124     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
125 
126     // Copy initializer elements. Skip padding fields.
127     unsigned EltNo = 0;  // Element no in ILE
128     unsigned FieldNo = 0; // Field no in  SType
129     while (EltNo < NumInitableElts) {
130 
131       // Zero initialize padding field.
132       if (CGR->isPaddingField(FieldNo)) {
133         const llvm::Type *FieldTy = SType->getElementType(FieldNo);
134         Elts.push_back(llvm::Constant::getNullValue(FieldTy));
135         FieldNo++;
136         continue;
137       }
138 
139       llvm::Constant *C = Visit(ILE->getInit(EltNo));
140       // FIXME: Remove this when sema of initializers is finished (and the code
141       // above).
142       if (C == 0 && ILE->getInit(EltNo)->getType()->isVoidType()) {
143         if (ILE->getType()->isVoidType()) return 0;
144         return llvm::UndefValue::get(SType);
145       }
146       assert (C && "Failed to create initializer expression");
147       Elts.push_back(C);
148       EltNo++;
149       FieldNo++;
150     }
151 
152     // Initialize remaining structure elements.
153     for (unsigned i = Elts.size(); i < NumElements; ++i) {
154       const llvm::Type *FieldTy = SType->getElementType(i);
155       Elts.push_back(llvm::Constant::getNullValue(FieldTy));
156     }
157 
158     return llvm::ConstantStruct::get(SType, Elts);
159   }
160 
161   llvm::Constant *EmitVectorInitialization(InitListExpr *ILE,
162                                            const llvm::VectorType *VType) {
163 
164     std::vector<llvm::Constant*> Elts;
165     unsigned NumInitElements = ILE->getNumInits();
166     unsigned NumElements = VType->getNumElements();
167 
168     assert (NumInitElements == NumElements
169             && "Unsufficient vector init elelments");
170     // Copy initializer elements.
171     unsigned i = 0;
172     for (; i < NumElements; ++i) {
173 
174       llvm::Constant *C = Visit(ILE->getInit(i));
175       // FIXME: Remove this when sema of initializers is finished (and the code
176       // above).
177       if (C == 0 && ILE->getInit(i)->getType()->isVoidType()) {
178         if (ILE->getType()->isVoidType()) return 0;
179         return llvm::UndefValue::get(VType);
180       }
181       assert (C && "Failed to create initializer expression");
182       Elts.push_back(C);
183     }
184 
185     return llvm::ConstantVector::get(VType, Elts);
186   }
187 
188   llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
189     const llvm::CompositeType *CType =
190       dyn_cast<llvm::CompositeType>(ConvertType(ILE->getType()));
191 
192     if (!CType) {
193         // We have a scalar in braces. Just use the first element.
194         return Visit(ILE->getInit(0));
195     }
196 
197     if (const llvm::ArrayType *AType = dyn_cast<llvm::ArrayType>(CType))
198       return EmitArrayInitialization(ILE, AType);
199 
200     if (const llvm::StructType *SType = dyn_cast<llvm::StructType>(CType))
201       return EmitStructInitialization(ILE, SType);
202 
203     if (const llvm::VectorType *VType = dyn_cast<llvm::VectorType>(CType))
204       return EmitVectorInitialization(ILE, VType);
205 
206     // Make sure we have an array at this point
207     assert(0 && "Unable to handle InitListExpr");
208     // Get rid of control reaches end of void function warning.
209     // Not reached.
210     return 0;
211   }
212 
213   llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
214     Expr* SExpr = ICExpr->getSubExpr();
215     QualType SType = SExpr->getType();
216     llvm::Constant *C; // the intermediate expression
217     QualType T;        // the type of the intermediate expression
218     if (SType->isArrayType()) {
219       // Arrays decay to a pointer to the first element
220       // VLAs would require special handling, but they can't occur here
221       C = EmitLValue(SExpr);
222       llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
223       llvm::Constant *Ops[] = {Idx0, Idx0};
224       C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
225 
226       QualType ElemType = SType->getAsArrayType()->getElementType();
227       T = CGM.getContext().getPointerType(ElemType);
228     } else if (SType->isFunctionType()) {
229       // Function types decay to a pointer to the function
230       C = EmitLValue(SExpr);
231       T = CGM.getContext().getPointerType(SType);
232     } else {
233       C = Visit(SExpr);
234       T = SType;
235     }
236 
237     // Perform the conversion; note that an implicit cast can both promote
238     // and convert an array/function
239     return EmitConversion(C, T, ICExpr->getType());
240   }
241 
242   llvm::Constant *VisitStringLiteral(StringLiteral *E) {
243     const char *StrData = E->getStrData();
244     unsigned Len = E->getByteLength();
245     assert(!E->getType()->isPointerType() && "Strings are always arrays");
246 
247     // Otherwise this must be a string initializing an array in a static
248     // initializer.  Don't emit it as the address of the string, emit the string
249     // data itself as an inline array.
250     const ConstantArrayType *CAT = E->getType()->getAsConstantArrayType();
251     assert(CAT && "String isn't pointer or array!");
252 
253     std::string Str(StrData, StrData + Len);
254     // Null terminate the string before potentially truncating it.
255     // FIXME: What about wchar_t strings?
256     Str.push_back(0);
257 
258     uint64_t RealLen = CAT->getSize().getZExtValue();
259     // String or grow the initializer to the required size.
260     if (RealLen != Str.size())
261       Str.resize(RealLen);
262 
263     return llvm::ConstantArray::get(Str, false);
264   }
265 
266   llvm::Constant *VisitDeclRefExpr(DeclRefExpr *E) {
267     const ValueDecl *Decl = E->getDecl();
268     if (const EnumConstantDecl *EC = dyn_cast<EnumConstantDecl>(Decl))
269       return llvm::ConstantInt::get(EC->getInitVal());
270     assert(0 && "Unsupported decl ref type!");
271     return 0;
272   }
273 
274   llvm::Constant *VisitSizeOfAlignOfTypeExpr(const SizeOfAlignOfTypeExpr *E) {
275     return EmitSizeAlignOf(E->getArgumentType(), E->getType(), E->isSizeOf());
276   }
277 
278   // Unary operators
279   llvm::Constant *VisitUnaryPlus(const UnaryOperator *E) {
280     return Visit(E->getSubExpr());
281   }
282   llvm::Constant *VisitUnaryMinus(const UnaryOperator *E) {
283     return llvm::ConstantExpr::getNeg(Visit(E->getSubExpr()));
284   }
285   llvm::Constant *VisitUnaryNot(const UnaryOperator *E) {
286     return llvm::ConstantExpr::getNot(Visit(E->getSubExpr()));
287   }
288   llvm::Constant *VisitUnaryLNot(const UnaryOperator *E) {
289     llvm::Constant *SubExpr = Visit(E->getSubExpr());
290 
291     if (E->getSubExpr()->getType()->isRealFloatingType()) {
292       // Compare against 0.0 for fp scalars.
293       llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
294       SubExpr = llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UEQ, SubExpr,
295                                             Zero);
296     } else {
297       assert((E->getSubExpr()->getType()->isIntegerType() ||
298               E->getSubExpr()->getType()->isPointerType()) &&
299              "Unknown scalar type to convert");
300       // Compare against an integer or pointer null.
301       llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
302       SubExpr = llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_EQ, SubExpr,
303                                             Zero);
304     }
305 
306     return llvm::ConstantExpr::getZExt(SubExpr, ConvertType(E->getType()));
307   }
308   llvm::Constant *VisitUnarySizeOf(const UnaryOperator *E) {
309     return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), true);
310   }
311   llvm::Constant *VisitUnaryAlignOf(const UnaryOperator *E) {
312     return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), false);
313   }
314   llvm::Constant *VisitUnaryAddrOf(const UnaryOperator *E) {
315     return EmitLValue(E->getSubExpr());
316   }
317   llvm::Constant *VisitUnaryOffsetOf(const UnaryOperator *E) {
318     int64_t Val = E->evaluateOffsetOf(CGM.getContext());
319 
320     assert(E->getType()->isIntegerType() && "Result type must be an integer!");
321 
322     uint32_t ResultWidth =
323       static_cast<uint32_t>(CGM.getContext().getTypeSize(E->getType()));
324     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
325   }
326 
327   // Binary operators
328   llvm::Constant *VisitBinOr(const BinaryOperator *E) {
329     llvm::Constant *LHS = Visit(E->getLHS());
330     llvm::Constant *RHS = Visit(E->getRHS());
331 
332     return llvm::ConstantExpr::getOr(LHS, RHS);
333   }
334   llvm::Constant *VisitBinSub(const BinaryOperator *E) {
335     llvm::Constant *LHS = Visit(E->getLHS());
336     llvm::Constant *RHS = Visit(E->getRHS());
337 
338     if (!isa<llvm::PointerType>(RHS->getType())) {
339       // pointer - int
340       if (isa<llvm::PointerType>(LHS->getType())) {
341         llvm::Constant *Idx = llvm::ConstantExpr::getNeg(RHS);
342 
343         return llvm::ConstantExpr::getGetElementPtr(LHS, &Idx, 1);
344       }
345 
346       // int - int
347       return llvm::ConstantExpr::getSub(LHS, RHS);
348     }
349 
350     assert(0 && "Unhandled bin sub case!");
351     return 0;
352   }
353 
354   llvm::Constant *VisitBinShl(const BinaryOperator *E) {
355     llvm::Constant *LHS = Visit(E->getLHS());
356     llvm::Constant *RHS = Visit(E->getRHS());
357 
358     // LLVM requires the LHS and RHS to be the same type: promote or truncate the
359     // RHS to the same size as the LHS.
360     if (LHS->getType() != RHS->getType())
361       RHS = llvm::ConstantExpr::getIntegerCast(RHS, LHS->getType(), false);
362 
363     return llvm::ConstantExpr::getShl(LHS, RHS);
364   }
365 
366   llvm::Constant *VisitBinMul(const BinaryOperator *E) {
367     llvm::Constant *LHS = Visit(E->getLHS());
368     llvm::Constant *RHS = Visit(E->getRHS());
369 
370     return llvm::ConstantExpr::getMul(LHS, RHS);
371   }
372 
373   llvm::Constant *VisitBinDiv(const BinaryOperator *E) {
374     llvm::Constant *LHS = Visit(E->getLHS());
375     llvm::Constant *RHS = Visit(E->getRHS());
376 
377     if (LHS->getType()->isFPOrFPVector())
378       return llvm::ConstantExpr::getFDiv(LHS, RHS);
379     else if (E->getType()->isUnsignedIntegerType())
380       return llvm::ConstantExpr::getUDiv(LHS, RHS);
381     else
382       return llvm::ConstantExpr::getSDiv(LHS, RHS);
383   }
384 
385   llvm::Constant *VisitBinAdd(const BinaryOperator *E) {
386     llvm::Constant *LHS = Visit(E->getLHS());
387     llvm::Constant *RHS = Visit(E->getRHS());
388 
389     if (!E->getType()->isPointerType())
390       return llvm::ConstantExpr::getAdd(LHS, RHS);
391 
392     llvm::Constant *Ptr, *Idx;
393     if (isa<llvm::PointerType>(LHS->getType())) { // pointer + int
394       Ptr = LHS;
395       Idx = RHS;
396     } else { // int + pointer
397       Ptr = RHS;
398       Idx = LHS;
399     }
400 
401     return llvm::ConstantExpr::getGetElementPtr(Ptr, &Idx, 1);
402   }
403 
404   llvm::Constant *VisitBinAnd(const BinaryOperator *E) {
405     llvm::Constant *LHS = Visit(E->getLHS());
406     llvm::Constant *RHS = Visit(E->getRHS());
407 
408     return llvm::ConstantExpr::getAnd(LHS, RHS);
409   }
410 
411   // Utility methods
412   const llvm::Type *ConvertType(QualType T) {
413     return CGM.getTypes().ConvertType(T);
414   }
415 
416   llvm::Constant *EmitConversionToBool(llvm::Constant *Src, QualType SrcType) {
417     assert(SrcType->isCanonical() && "EmitConversion strips typedefs");
418 
419     if (SrcType->isRealFloatingType()) {
420       // Compare against 0.0 for fp scalars.
421       llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
422       return llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UNE, Src, Zero);
423     }
424 
425     assert((SrcType->isIntegerType() || SrcType->isPointerType()) &&
426            "Unknown scalar type to convert");
427 
428     // Compare against an integer or pointer null.
429     llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
430     return llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_NE, Src, Zero);
431   }
432 
433   llvm::Constant *EmitConversion(llvm::Constant *Src, QualType SrcType,
434                                  QualType DstType) {
435     SrcType = SrcType.getCanonicalType();
436     DstType = DstType.getCanonicalType();
437     if (SrcType == DstType) return Src;
438 
439     // Handle conversions to bool first, they are special: comparisons against 0.
440     if (DstType->isBooleanType())
441       return EmitConversionToBool(Src, SrcType);
442 
443     const llvm::Type *DstTy = ConvertType(DstType);
444 
445     // Ignore conversions like int -> uint.
446     if (Src->getType() == DstTy)
447       return Src;
448 
449     // Handle pointer conversions next: pointers can only be converted to/from
450     // other pointers and integers.
451     if (isa<PointerType>(DstType)) {
452       // The source value may be an integer, or a pointer.
453       if (isa<llvm::PointerType>(Src->getType()))
454         return llvm::ConstantExpr::getBitCast(Src, DstTy);
455       assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
456       return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
457     }
458 
459     if (isa<PointerType>(SrcType)) {
460       // Must be an ptr to int cast.
461       assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
462       return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
463     }
464 
465     // A scalar source can be splatted to a vector of the same element type
466     if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
467       const llvm::VectorType *VT = cast<llvm::VectorType>(DstTy);
468       assert((VT->getElementType() == Src->getType()) &&
469              "Vector element type must match scalar type to splat.");
470       unsigned NumElements = DstType->getAsVectorType()->getNumElements();
471       llvm::SmallVector<llvm::Constant*, 16> Elements;
472       for (unsigned i = 0; i < NumElements; i++)
473         Elements.push_back(Src);
474 
475       return llvm::ConstantVector::get(&Elements[0], NumElements);
476     }
477 
478     if (isa<llvm::VectorType>(Src->getType()) ||
479         isa<llvm::VectorType>(DstTy)) {
480       return llvm::ConstantExpr::getBitCast(Src, DstTy);
481     }
482 
483     // Finally, we have the arithmetic types: real int/float.
484     if (isa<llvm::IntegerType>(Src->getType())) {
485       bool InputSigned = SrcType->isSignedIntegerType();
486       if (isa<llvm::IntegerType>(DstTy))
487         return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
488       else if (InputSigned)
489         return llvm::ConstantExpr::getSIToFP(Src, DstTy);
490       else
491         return llvm::ConstantExpr::getUIToFP(Src, DstTy);
492     }
493 
494     assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
495     if (isa<llvm::IntegerType>(DstTy)) {
496       if (DstType->isSignedIntegerType())
497         return llvm::ConstantExpr::getFPToSI(Src, DstTy);
498       else
499         return llvm::ConstantExpr::getFPToUI(Src, DstTy);
500     }
501 
502     assert(DstTy->isFloatingPoint() && "Unknown real conversion");
503     if (DstTy->getTypeID() < Src->getType()->getTypeID())
504       return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
505     else
506       return llvm::ConstantExpr::getFPExtend(Src, DstTy);
507   }
508 
509   llvm::Constant *EmitSizeAlignOf(QualType TypeToSize,
510                                   QualType RetType, bool isSizeOf) {
511     std::pair<uint64_t, unsigned> Info =
512       CGM.getContext().getTypeInfo(TypeToSize);
513 
514     uint64_t Val = isSizeOf ? Info.first : Info.second;
515     Val /= 8;  // Return size in bytes, not bits.
516 
517     assert(RetType->isIntegerType() && "Result type must be an integer!");
518 
519     uint32_t ResultWidth =
520       static_cast<uint32_t>(CGM.getContext().getTypeSize(RetType));
521     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
522   }
523 
524   llvm::Constant *EmitLValue(Expr *E) {
525     switch (E->getStmtClass()) {
526     default: break;
527     case Expr::ParenExprClass:
528       // Elide parenthesis
529       return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
530     case Expr::CompoundLiteralExprClass: {
531       // Note that due to the nature of compound literals, this is guaranteed
532       // to be the only use of the variable, so we just generate it here.
533       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
534       llvm::Constant* C = Visit(CLE->getInitializer());
535       C = new llvm::GlobalVariable(C->getType(),E->getType().isConstQualified(),
536                                    llvm::GlobalValue::InternalLinkage,
537                                    C, ".compoundliteral", &CGM.getModule());
538       return C;
539     }
540     case Expr::DeclRefExprClass: {
541       ValueDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
542       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
543         return CGM.GetAddrOfFunctionDecl(FD, false);
544       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
545         if (VD->isFileVarDecl())
546           return CGM.GetAddrOfGlobalVar(VD, false);
547         else if (VD->isBlockVarDecl()) {
548           assert(CGF && "Can't access static local vars without CGF");
549           return CGF->GetAddrOfStaticLocalVar(VD);
550         }
551       }
552       break;
553     }
554     case Expr::MemberExprClass: {
555       MemberExpr* ME = cast<MemberExpr>(E);
556       llvm::Constant *Base;
557       if (ME->isArrow())
558         Base = Visit(ME->getBase());
559       else
560         Base = EmitLValue(ME->getBase());
561 
562       unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(ME->getMemberDecl());
563       llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
564       llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
565                                                    FieldNumber);
566       llvm::Value *Ops[] = {Zero, Idx};
567       return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
568     }
569     case Expr::ArraySubscriptExprClass: {
570       ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
571       llvm::Constant *Base = Visit(ASExpr->getBase());
572       llvm::Constant *Index = Visit(ASExpr->getIdx());
573       assert(!ASExpr->getBase()->getType()->isVectorType() &&
574              "Taking the address of a vector component is illegal!");
575       return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
576     }
577     case Expr::StringLiteralClass: {
578       StringLiteral *String = cast<StringLiteral>(E);
579       assert(!String->isWide() && "Cannot codegen wide strings yet");
580       const char *StrData = String->getStrData();
581       unsigned Len = String->getByteLength();
582 
583       return CGM.GetAddrOfConstantString(std::string(StrData, StrData + Len));
584     }
585     case Expr::UnaryOperatorClass: {
586       UnaryOperator *Exp = cast<UnaryOperator>(E);
587       switch (Exp->getOpcode()) {
588       default: break;
589       case UnaryOperator::Extension:
590         // Extension is just a wrapper for expressions
591         return EmitLValue(Exp->getSubExpr());
592       case UnaryOperator::Real:
593       case UnaryOperator::Imag: {
594         // The address of __real or __imag is just a GEP off the address
595         // of the internal expression
596         llvm::Constant* C = EmitLValue(Exp->getSubExpr());
597         llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
598         llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
599                                        Exp->getOpcode() == UnaryOperator::Imag);
600         llvm::Value *Ops[] = {Zero, Idx};
601         return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
602       }
603       case UnaryOperator::Deref:
604         // The address of a deref is just the value of the expression
605         return Visit(Exp->getSubExpr());
606       }
607       break;
608     }
609     }
610     CGM.WarnUnsupported(E, "constant l-value expression");
611     llvm::Type *Ty = llvm::PointerType::getUnqual(ConvertType(E->getType()));
612     return llvm::UndefValue::get(Ty);
613   }
614 
615 };
616 
617 }  // end anonymous namespace.
618 
619 
620 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
621                                                 CodeGenFunction *CGF)
622 {
623   QualType type = E->getType().getCanonicalType();
624 
625   if (type->isIntegerType()) {
626     llvm::APSInt Value(static_cast<uint32_t>(Context.getTypeSize(type)));
627     if (E->isIntegerConstantExpr(Value, Context)) {
628       return llvm::ConstantInt::get(Value);
629     }
630   }
631 
632   return ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
633 }
634