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/StmtVisitor.h"
20 #include "llvm/Constants.h"
21 #include "llvm/Function.h"
22 #include "llvm/GlobalVariable.h"
23 #include "llvm/Support/Compiler.h"
24 #include "llvm/Target/TargetData.h"
25 using namespace clang;
26 using namespace CodeGen;
27 
28 namespace  {
29 class VISIBILITY_HIDDEN ConstExprEmitter :
30   public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
31   CodeGenModule &CGM;
32   CodeGenFunction *CGF;
33 public:
34   ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
35     : CGM(cgm), CGF(cgf) {
36   }
37 
38   //===--------------------------------------------------------------------===//
39   //                            Visitor Methods
40   //===--------------------------------------------------------------------===//
41 
42   llvm::Constant *VisitStmt(Stmt *S) {
43     CGM.ErrorUnsupported(S, "constant expression");
44     QualType T = cast<Expr>(S)->getType();
45     return llvm::UndefValue::get(CGM.getTypes().ConvertType(T));
46   }
47 
48   llvm::Constant *VisitParenExpr(ParenExpr *PE) {
49     return Visit(PE->getSubExpr());
50   }
51 
52   llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
53     return Visit(E->getInitializer());
54   }
55 
56   llvm::Constant *VisitCastExpr(CastExpr* E) {
57     // GCC cast to union extension
58     if (E->getType()->isUnionType()) {
59       const llvm::Type *Ty = ConvertType(E->getType());
60       return EmitUnion(CGM.EmitConstantExpr(E->getSubExpr(), CGF), Ty);
61     }
62 
63     llvm::Constant *C = Visit(E->getSubExpr());
64 
65     return EmitConversion(C, E->getSubExpr()->getType(), E->getType());
66   }
67 
68   llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
69     return Visit(DAE->getExpr());
70   }
71 
72   llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
73     std::vector<llvm::Constant*> Elts;
74     const llvm::ArrayType *AType =
75         cast<llvm::ArrayType>(ConvertType(ILE->getType()));
76     unsigned NumInitElements = ILE->getNumInits();
77     // FIXME: Check for wide strings
78     if (NumInitElements > 0 && isa<StringLiteral>(ILE->getInit(0)) &&
79         ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
80       return Visit(ILE->getInit(0));
81     const llvm::Type *ElemTy = AType->getElementType();
82     unsigned NumElements = AType->getNumElements();
83 
84     // Initialising an array requires us to automatically
85     // initialise any elements that have not been initialised explicitly
86     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
87 
88     // Copy initializer elements.
89     unsigned i = 0;
90     bool RewriteType = false;
91     for (; i < NumInitableElts; ++i) {
92       llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(i), CGF);
93       RewriteType |= (C->getType() != ElemTy);
94       Elts.push_back(C);
95     }
96 
97     // Initialize remaining array elements.
98     for (; i < NumElements; ++i)
99       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
100 
101     if (RewriteType) {
102       // FIXME: Try to avoid packing the array
103       std::vector<const llvm::Type*> Types;
104       for (unsigned i = 0; i < Elts.size(); ++i)
105         Types.push_back(Elts[i]->getType());
106       const llvm::StructType *SType = llvm::StructType::get(Types, true);
107       return llvm::ConstantStruct::get(SType, Elts);
108     }
109 
110     return llvm::ConstantArray::get(AType, Elts);
111   }
112 
113   void InsertBitfieldIntoStruct(std::vector<llvm::Constant*>& Elts,
114                                 FieldDecl* Field, Expr* E) {
115     // Calculate the value to insert
116     llvm::Constant *C = CGM.EmitConstantExpr(E, CGF);
117     llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
118     if (!CI) {
119       CGM.ErrorUnsupported(E, "bitfield initialization");
120       return;
121     }
122     llvm::APInt V = CI->getValue();
123 
124     // Calculate information about the relevant field
125     const llvm::Type* Ty = CI->getType();
126     const llvm::TargetData &TD = CGM.getTypes().getTargetData();
127     unsigned size = TD.getTypeStoreSizeInBits(Ty);
128     unsigned fieldOffset = CGM.getTypes().getLLVMFieldNo(Field) * size;
129     CodeGenTypes::BitFieldInfo bitFieldInfo =
130         CGM.getTypes().getBitFieldInfo(Field);
131     fieldOffset += bitFieldInfo.Begin;
132 
133     // Find where to start the insertion
134     // FIXME: This is O(n^2) in the number of bit-fields!
135     // FIXME: This won't work if the struct isn't completely packed!
136     unsigned offset = 0, i = 0;
137     while (offset < (fieldOffset & -8))
138       offset += TD.getTypeStoreSizeInBits(Elts[i++]->getType());
139 
140     // Advance over 0 sized elements (must terminate in bounds since
141     // the bitfield must have a size).
142     while (TD.getTypeStoreSizeInBits(Elts[i]->getType()) == 0)
143       ++i;
144 
145     // Promote the size of V if necessary
146     // FIXME: This should never occur, but currently it can because
147     // initializer constants are cast to bool, and because clang is
148     // not enforcing bitfield width limits.
149     if (bitFieldInfo.Size > V.getBitWidth())
150       V.zext(bitFieldInfo.Size);
151 
152     // Insert the bits into the struct
153     // FIXME: This algorthm is only correct on X86!
154     // FIXME: THis algorthm assumes bit-fields only have byte-size elements!
155     unsigned bitsToInsert = bitFieldInfo.Size;
156     unsigned curBits = std::min(8 - (fieldOffset & 7), bitsToInsert);
157     unsigned byte = V.getLoBits(curBits).getZExtValue() << (fieldOffset & 7);
158     do {
159       llvm::Constant* byteC = llvm::ConstantInt::get(llvm::Type::Int8Ty, byte);
160       Elts[i] = llvm::ConstantExpr::getOr(Elts[i], byteC);
161       ++i;
162       V = V.lshr(curBits);
163       bitsToInsert -= curBits;
164 
165       if (!bitsToInsert)
166         break;
167 
168       curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
169       byte = V.getLoBits(curBits).getZExtValue();
170     } while (true);
171   }
172 
173   llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
174     const llvm::StructType *SType =
175         cast<llvm::StructType>(ConvertType(ILE->getType()));
176     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
177     std::vector<llvm::Constant*> Elts;
178 
179     // Initialize the whole structure to zero.
180     for (unsigned i = 0; i < SType->getNumElements(); ++i) {
181       const llvm::Type *FieldTy = SType->getElementType(i);
182       Elts.push_back(llvm::Constant::getNullValue(FieldTy));
183     }
184 
185     // Copy initializer elements. Skip padding fields.
186     unsigned EltNo = 0;  // Element no in ILE
187     int FieldNo = 0; // Field no in RecordDecl
188     bool RewriteType = false;
189     for (RecordDecl::field_iterator Field = RD->field_begin(),
190                                  FieldEnd = RD->field_end();
191          EltNo < ILE->getNumInits() && Field != FieldEnd; ++Field) {
192       FieldNo++;
193       if (!Field->getIdentifier())
194         continue;
195 
196       if (Field->isBitField()) {
197         InsertBitfieldIntoStruct(Elts, *Field, ILE->getInit(EltNo));
198       } else {
199         unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(*Field);
200         llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(EltNo), CGF);
201         RewriteType |= (C->getType() != Elts[FieldNo]->getType());
202         Elts[FieldNo] = C;
203       }
204       EltNo++;
205     }
206 
207     if (RewriteType) {
208       // FIXME: Make this work for non-packed structs
209       assert(SType->isPacked() && "Cannot recreate unpacked structs");
210       std::vector<const llvm::Type*> Types;
211       for (unsigned i = 0; i < Elts.size(); ++i)
212         Types.push_back(Elts[i]->getType());
213       SType = llvm::StructType::get(Types, true);
214     }
215 
216     return llvm::ConstantStruct::get(SType, Elts);
217   }
218 
219   llvm::Constant *EmitUnion(llvm::Constant *C, const llvm::Type *Ty) {
220     // Build a struct with the union sub-element as the first member,
221     // and padded to the appropriate size
222     std::vector<llvm::Constant*> Elts;
223     std::vector<const llvm::Type*> Types;
224     Elts.push_back(C);
225     Types.push_back(C->getType());
226     unsigned CurSize = CGM.getTargetData().getTypeStoreSize(C->getType());
227     unsigned TotalSize = CGM.getTargetData().getTypeStoreSize(Ty);
228     while (CurSize < TotalSize) {
229       Elts.push_back(llvm::Constant::getNullValue(llvm::Type::Int8Ty));
230       Types.push_back(llvm::Type::Int8Ty);
231       CurSize++;
232     }
233 
234     // This always generates a packed struct
235     // FIXME: Try to generate an unpacked struct when we can
236     llvm::StructType* STy = llvm::StructType::get(Types, true);
237     return llvm::ConstantStruct::get(STy, Elts);
238   }
239 
240   llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
241     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
242     const llvm::Type *Ty = ConvertType(ILE->getType());
243 
244     // Find the field decl we're initializing, if any
245     // FIXME: C99 designated initializers won't always initialize the
246     // first field
247     int FieldNo = 0; // Field no in RecordDecl
248     FieldDecl* curField = 0;
249     bool sawAnyFields = false;
250     for (RecordDecl::field_iterator Field = RD->field_begin(),
251                                  FieldEnd = RD->field_end();
252          Field != FieldEnd; ++Field) {
253       curField = *Field;
254       FieldNo++;
255 
256       if (curField->isUnnamedBitfield())
257         continue;
258 
259       // If we have an initializer, find the field whose type is the
260       // same as that initializer. This
261       sawAnyFields = true;
262       if (ILE->getNumInits() > 0 &&
263           CGM.getContext().getCanonicalType(curField->getType()) ==
264             CGM.getContext().getCanonicalType(ILE->getInit(0)->getType()))
265         break;
266     }
267 
268     if (!curField || !curField->getIdentifier() || ILE->getNumInits() == 0)
269       return llvm::Constant::getNullValue(Ty);
270 
271     if (curField->isBitField()) {
272       // Create a dummy struct for bit-field insertion
273       unsigned NumElts = CGM.getTargetData().getTypePaddedSize(Ty) / 8;
274       llvm::Constant* NV = llvm::Constant::getNullValue(llvm::Type::Int8Ty);
275       std::vector<llvm::Constant*> Elts(NumElts, NV);
276 
277       InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
278       const llvm::ArrayType *RetTy =
279           llvm::ArrayType::get(NV->getType(), NumElts);
280       return llvm::ConstantArray::get(RetTy, Elts);
281     }
282 
283     return EmitUnion(CGM.EmitConstantExpr(ILE->getInit(0), CGF), Ty);
284   }
285 
286   llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
287     const llvm::VectorType *VType =
288         cast<llvm::VectorType>(ConvertType(ILE->getType()));
289     const llvm::Type *ElemTy = VType->getElementType();
290     std::vector<llvm::Constant*> Elts;
291     unsigned NumElements = VType->getNumElements();
292     unsigned NumInitElements = ILE->getNumInits();
293 
294     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
295 
296     // Copy initializer elements.
297     unsigned i = 0;
298     for (; i < NumInitableElts; ++i) {
299       llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(i), CGF);
300       Elts.push_back(C);
301     }
302 
303     for (; i < NumElements; ++i)
304       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
305 
306     return llvm::ConstantVector::get(VType, Elts);
307   }
308 
309   llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
310     if (ILE->getType()->isScalarType()) {
311       // We have a scalar in braces. Just use the first element.
312       if (ILE->getNumInits() > 0)
313         return CGM.EmitConstantExpr(ILE->getInit(0), CGF);
314 
315       const llvm::Type* RetTy = CGM.getTypes().ConvertType(ILE->getType());
316       return llvm::Constant::getNullValue(RetTy);
317     }
318 
319     if (ILE->getType()->isArrayType())
320       return EmitArrayInitialization(ILE);
321 
322     if (ILE->getType()->isStructureType())
323       return EmitStructInitialization(ILE);
324 
325     if (ILE->getType()->isUnionType())
326       return EmitUnionInitialization(ILE);
327 
328     if (ILE->getType()->isVectorType())
329       return EmitVectorInitialization(ILE);
330 
331     assert(0 && "Unable to handle InitListExpr");
332     // Get rid of control reaches end of void function warning.
333     // Not reached.
334     return 0;
335   }
336 
337   llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
338     Expr* SExpr = ICExpr->getSubExpr();
339     QualType SType = SExpr->getType();
340     llvm::Constant *C; // the intermediate expression
341     QualType T;        // the type of the intermediate expression
342     if (SType->isArrayType()) {
343       // Arrays decay to a pointer to the first element
344       // VLAs would require special handling, but they can't occur here
345       C = EmitLValue(SExpr);
346       llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
347       llvm::Constant *Ops[] = {Idx0, Idx0};
348       C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
349       T = CGM.getContext().getArrayDecayedType(SType);
350     } else if (SType->isFunctionType()) {
351       // Function types decay to a pointer to the function
352       C = EmitLValue(SExpr);
353       T = CGM.getContext().getPointerType(SType);
354     } else {
355       C = Visit(SExpr);
356       T = SType;
357     }
358 
359     // Perform the conversion; note that an implicit cast can both promote
360     // and convert an array/function
361     return EmitConversion(C, T, ICExpr->getType());
362   }
363 
364   llvm::Constant *VisitStringLiteral(StringLiteral *E) {
365     assert(!E->getType()->isPointerType() && "Strings are always arrays");
366 
367     // Otherwise this must be a string initializing an array in a static
368     // initializer.  Don't emit it as the address of the string, emit the string
369     // data itself as an inline array.
370     return llvm::ConstantArray::get(CGM.GetStringForStringLiteral(E), false);
371   }
372 
373   llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
374     return Visit(E->getSubExpr());
375   }
376 
377   // Utility methods
378   const llvm::Type *ConvertType(QualType T) {
379     return CGM.getTypes().ConvertType(T);
380   }
381 
382   llvm::Constant *EmitConversionToBool(llvm::Constant *Src, QualType SrcType) {
383     assert(SrcType->isCanonical() && "EmitConversion strips typedefs");
384 
385     if (SrcType->isRealFloatingType()) {
386       // Compare against 0.0 for fp scalars.
387       llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
388       return llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UNE, Src, Zero);
389     }
390 
391     assert((SrcType->isIntegerType() || SrcType->isPointerType()) &&
392            "Unknown scalar type to convert");
393 
394     // Compare against an integer or pointer null.
395     llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
396     return llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_NE, Src, Zero);
397   }
398 
399   llvm::Constant *EmitConversion(llvm::Constant *Src, QualType SrcType,
400                                  QualType DstType) {
401     SrcType = CGM.getContext().getCanonicalType(SrcType);
402     DstType = CGM.getContext().getCanonicalType(DstType);
403     if (SrcType == DstType) return Src;
404 
405     // Handle conversions to bool first, they are special: comparisons against 0.
406     if (DstType->isBooleanType())
407       return EmitConversionToBool(Src, SrcType);
408 
409     const llvm::Type *DstTy = ConvertType(DstType);
410 
411     // Ignore conversions like int -> uint.
412     if (Src->getType() == DstTy)
413       return Src;
414 
415     // Handle pointer conversions next: pointers can only be converted to/from
416     // other pointers and integers.
417     if (isa<llvm::PointerType>(DstTy)) {
418       // The source value may be an integer, or a pointer.
419       if (isa<llvm::PointerType>(Src->getType()))
420         return llvm::ConstantExpr::getBitCast(Src, DstTy);
421       assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
422       return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
423     }
424 
425     if (isa<llvm::PointerType>(Src->getType())) {
426       // Must be an ptr to int cast.
427       assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
428       return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
429     }
430 
431     // A scalar source can be splatted to a vector of the same element type
432     if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
433       assert((cast<llvm::VectorType>(DstTy)->getElementType()
434               == Src->getType()) &&
435              "Vector element type must match scalar type to splat.");
436       unsigned NumElements = DstType->getAsVectorType()->getNumElements();
437       llvm::SmallVector<llvm::Constant*, 16> Elements;
438       for (unsigned i = 0; i < NumElements; i++)
439         Elements.push_back(Src);
440 
441       return llvm::ConstantVector::get(&Elements[0], NumElements);
442     }
443 
444     if (isa<llvm::VectorType>(Src->getType()) ||
445         isa<llvm::VectorType>(DstTy)) {
446       return llvm::ConstantExpr::getBitCast(Src, DstTy);
447     }
448 
449     // Finally, we have the arithmetic types: real int/float.
450     if (isa<llvm::IntegerType>(Src->getType())) {
451       bool InputSigned = SrcType->isSignedIntegerType();
452       if (isa<llvm::IntegerType>(DstTy))
453         return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
454       else if (InputSigned)
455         return llvm::ConstantExpr::getSIToFP(Src, DstTy);
456       else
457         return llvm::ConstantExpr::getUIToFP(Src, DstTy);
458     }
459 
460     assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
461     if (isa<llvm::IntegerType>(DstTy)) {
462       if (DstType->isSignedIntegerType())
463         return llvm::ConstantExpr::getFPToSI(Src, DstTy);
464       else
465         return llvm::ConstantExpr::getFPToUI(Src, DstTy);
466     }
467 
468     assert(DstTy->isFloatingPoint() && "Unknown real conversion");
469     if (DstTy->getTypeID() < Src->getType()->getTypeID())
470       return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
471     else
472       return llvm::ConstantExpr::getFPExtend(Src, DstTy);
473   }
474 
475 public:
476   llvm::Constant *EmitLValue(Expr *E) {
477     switch (E->getStmtClass()) {
478     default: break;
479     case Expr::ParenExprClass:
480       // Elide parenthesis
481       return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
482     case Expr::CompoundLiteralExprClass: {
483       // Note that due to the nature of compound literals, this is guaranteed
484       // to be the only use of the variable, so we just generate it here.
485       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
486       llvm::Constant* C = Visit(CLE->getInitializer());
487       C = new llvm::GlobalVariable(C->getType(),E->getType().isConstQualified(),
488                                    llvm::GlobalValue::InternalLinkage,
489                                    C, ".compoundliteral", &CGM.getModule());
490       return C;
491     }
492     case Expr::DeclRefExprClass:
493     case Expr::QualifiedDeclRefExprClass: {
494       NamedDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
495       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
496         return CGM.GetAddrOfFunction(FD);
497       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
498         if (VD->isFileVarDecl())
499           return CGM.GetAddrOfGlobalVar(VD);
500         else if (VD->isBlockVarDecl()) {
501           assert(CGF && "Can't access static local vars without CGF");
502           return CGF->GetAddrOfStaticLocalVar(VD);
503         }
504       }
505       break;
506     }
507     case Expr::MemberExprClass: {
508       MemberExpr* ME = cast<MemberExpr>(E);
509       llvm::Constant *Base;
510       if (ME->isArrow())
511         Base = Visit(ME->getBase());
512       else
513         Base = EmitLValue(ME->getBase());
514 
515       FieldDecl *Field = dyn_cast<FieldDecl>(ME->getMemberDecl());
516       // FIXME: Handle other kinds of member expressions.
517       assert(Field && "No code generation for non-field member expressions");
518       unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(Field);
519       llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
520       llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
521                                                    FieldNumber);
522       llvm::Value *Ops[] = {Zero, Idx};
523       return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
524     }
525     case Expr::ArraySubscriptExprClass: {
526       ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
527       llvm::Constant *Base = Visit(ASExpr->getBase());
528       llvm::Constant *Index = Visit(ASExpr->getIdx());
529       assert(!ASExpr->getBase()->getType()->isVectorType() &&
530              "Taking the address of a vector component is illegal!");
531       return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
532     }
533     case Expr::StringLiteralClass:
534       return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
535     case Expr::ObjCStringLiteralClass: {
536       ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
537       std::string S(SL->getString()->getStrData(),
538                     SL->getString()->getByteLength());
539       llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(S);
540       return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
541     }
542     case Expr::UnaryOperatorClass: {
543       UnaryOperator *Exp = cast<UnaryOperator>(E);
544       switch (Exp->getOpcode()) {
545       default: break;
546       case UnaryOperator::Extension:
547         // Extension is just a wrapper for expressions
548         return EmitLValue(Exp->getSubExpr());
549       case UnaryOperator::Real:
550       case UnaryOperator::Imag: {
551         // The address of __real or __imag is just a GEP off the address
552         // of the internal expression
553         llvm::Constant* C = EmitLValue(Exp->getSubExpr());
554         llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
555         llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
556                                        Exp->getOpcode() == UnaryOperator::Imag);
557         llvm::Value *Ops[] = {Zero, Idx};
558         return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
559       }
560       case UnaryOperator::Deref:
561         // The address of a deref is just the value of the expression
562         return Visit(Exp->getSubExpr());
563       }
564       break;
565     }
566 
567     case Expr::PredefinedExprClass: {
568       // __func__/__FUNCTION__ -> "".  __PRETTY_FUNCTION__ -> "top level".
569       std::string Str;
570       if (cast<PredefinedExpr>(E)->getIdentType() ==
571           PredefinedExpr::PrettyFunction)
572         Str = "top level";
573 
574       return CGM.GetAddrOfConstantCString(Str, ".tmp");
575     }
576     case Expr::AddrLabelExprClass: {
577       assert(CGF && "Invalid address of label expression outside function.");
578       unsigned id = CGF->GetIDForAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
579       llvm::Constant *C = llvm::ConstantInt::get(llvm::Type::Int32Ty, id);
580       return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
581     }
582     case Expr::CallExprClass: {
583       CallExpr* CE = cast<CallExpr>(E);
584       if (CE->isBuiltinCall() != Builtin::BI__builtin___CFStringMakeConstantString)
585         break;
586       const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
587       const StringLiteral *Literal = cast<StringLiteral>(Arg);
588       std::string S(Literal->getStrData(), Literal->getByteLength());
589       return CGM.GetAddrOfConstantCFString(S);
590     }
591     }
592     CGM.ErrorUnsupported(E, "constant l-value expression");
593     llvm::Type *Ty = llvm::PointerType::getUnqual(ConvertType(E->getType()));
594     return llvm::UndefValue::get(Ty);
595   }
596 };
597 
598 }  // end anonymous namespace.
599 
600 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
601                                                 CodeGenFunction *CGF) {
602   QualType type = Context.getCanonicalType(E->getType());
603 
604   Expr::EvalResult Result;
605 
606   if (E->Evaluate(Result, Context)) {
607     assert(!Result.HasSideEffects &&
608            "Constant expr should not have any side effects!");
609     switch (Result.Val.getKind()) {
610     case APValue::Uninitialized:
611       assert(0 && "Constant expressions should be uninitialized.");
612       return llvm::UndefValue::get(getTypes().ConvertType(type));
613     case APValue::LValue: {
614       llvm::Constant *Offset =
615         llvm::ConstantInt::get(llvm::Type::Int64Ty,
616                                Result.Val.getLValueOffset());
617 
618       if (const Expr *LVBase = Result.Val.getLValueBase()) {
619         llvm::Constant *C =
620           ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
621 
622         const llvm::Type *Type =
623           llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
624         const llvm::Type *DestType = getTypes().ConvertTypeForMem(E->getType());
625 
626         // FIXME: It's a little ugly that we need to cast to a pointer,
627         // apply the GEP and then cast back.
628         C = llvm::ConstantExpr::getBitCast(C, Type);
629         C = llvm::ConstantExpr::getGetElementPtr(C, &Offset, 1);
630 
631         return llvm::ConstantExpr::getBitCast(C, DestType);
632       }
633 
634       return llvm::ConstantExpr::getIntToPtr(Offset,
635                                              getTypes().ConvertType(type));
636     }
637     case APValue::Int: {
638       llvm::Constant *C = llvm::ConstantInt::get(Result.Val.getInt());
639 
640       if (C->getType() == llvm::Type::Int1Ty) {
641         const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
642         C = llvm::ConstantExpr::getZExt(C, BoolTy);
643       }
644       return C;
645     }
646     case APValue::ComplexInt: {
647       llvm::Constant *Complex[2];
648 
649       Complex[0] = llvm::ConstantInt::get(Result.Val.getComplexIntReal());
650       Complex[1] = llvm::ConstantInt::get(Result.Val.getComplexIntImag());
651 
652       return llvm::ConstantStruct::get(Complex, 2);
653     }
654     case APValue::Float:
655       return llvm::ConstantFP::get(Result.Val.getFloat());
656     case APValue::ComplexFloat: {
657       llvm::Constant *Complex[2];
658 
659       Complex[0] = llvm::ConstantFP::get(Result.Val.getComplexFloatReal());
660       Complex[1] = llvm::ConstantFP::get(Result.Val.getComplexFloatImag());
661 
662       return llvm::ConstantStruct::get(Complex, 2);
663     }
664     case APValue::Vector: {
665       llvm::SmallVector<llvm::Constant *, 4> Inits;
666       unsigned NumElts = Result.Val.getVectorLength();
667 
668       for (unsigned i = 0; i != NumElts; ++i) {
669         APValue &Elt = Result.Val.getVectorElt(i);
670         if (Elt.isInt())
671           Inits.push_back(llvm::ConstantInt::get(Elt.getInt()));
672         else
673           Inits.push_back(llvm::ConstantFP::get(Elt.getFloat()));
674       }
675       return llvm::ConstantVector::get(&Inits[0], Inits.size());
676     }
677     }
678   }
679 
680   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
681   if (C->getType() == llvm::Type::Int1Ty) {
682     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
683     C = llvm::ConstantExpr::getZExt(C, BoolTy);
684   }
685   return C;
686 }
687