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 *VisitObjCStringLiteral(const ObjCStringLiteral *E) {
53     std::string S(E->getString()->getStrData(),
54                   E->getString()->getByteLength());
55     llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(S);
56     return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
57   }
58 
59   llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
60     return Visit(E->getInitializer());
61   }
62 
63   llvm::Constant *VisitCastExpr(CastExpr* E) {
64     llvm::Constant *C = Visit(E->getSubExpr());
65 
66     return EmitConversion(C, E->getSubExpr()->getType(), E->getType());
67   }
68 
69   llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
70     return Visit(DAE->getExpr());
71   }
72 
73   llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
74     std::vector<llvm::Constant*> Elts;
75     const llvm::ArrayType *AType =
76         cast<llvm::ArrayType>(ConvertType(ILE->getType()));
77     unsigned NumInitElements = ILE->getNumInits();
78     // FIXME: Check for wide strings
79     if (NumInitElements > 0 && isa<StringLiteral>(ILE->getInit(0)) &&
80         ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
81       return Visit(ILE->getInit(0));
82     const llvm::Type *ElemTy = AType->getElementType();
83     unsigned NumElements = AType->getNumElements();
84 
85     // Initialising an array requires us to automatically
86     // initialise any elements that have not been initialised explicitly
87     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
88 
89     // Copy initializer elements.
90     unsigned i = 0;
91     bool RewriteType = false;
92     for (; i < NumInitableElts; ++i) {
93       llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(i), CGF);
94       RewriteType |= (C->getType() != ElemTy);
95       Elts.push_back(C);
96     }
97 
98     // Initialize remaining array elements.
99     for (; i < NumElements; ++i)
100       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
101 
102     if (RewriteType) {
103       // FIXME: Try to avoid packing the array
104       std::vector<const llvm::Type*> Types;
105       for (unsigned i = 0; i < Elts.size(); ++i)
106         Types.push_back(Elts[i]->getType());
107       const llvm::StructType *SType = llvm::StructType::get(Types, true);
108       return llvm::ConstantStruct::get(SType, Elts);
109     }
110 
111     return llvm::ConstantArray::get(AType, Elts);
112   }
113 
114   void InsertBitfieldIntoStruct(std::vector<llvm::Constant*>& Elts,
115                                 FieldDecl* Field, Expr* E) {
116     // Calculate the value to insert
117     llvm::Constant *C = CGM.EmitConstantExpr(E, CGF);
118     llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
119     if (!CI) {
120       CGM.ErrorUnsupported(E, "bitfield initialization");
121       return;
122     }
123     llvm::APInt V = CI->getValue();
124 
125     // Calculate information about the relevant field
126     const llvm::Type* Ty = CI->getType();
127     const llvm::TargetData &TD = CGM.getTypes().getTargetData();
128     unsigned size = TD.getTypeStoreSizeInBits(Ty);
129     unsigned fieldOffset = CGM.getTypes().getLLVMFieldNo(Field) * size;
130     CodeGenTypes::BitFieldInfo bitFieldInfo =
131         CGM.getTypes().getBitFieldInfo(Field);
132     fieldOffset += bitFieldInfo.Begin;
133 
134     // Find where to start the insertion
135     // FIXME: This is O(n^2) in the number of bit-fields!
136     // FIXME: This won't work if the struct isn't completely packed!
137     unsigned offset = 0, i = 0;
138     while (offset < (fieldOffset & -8))
139       offset += TD.getTypeStoreSizeInBits(Elts[i++]->getType());
140 
141     // Advance over 0 sized elements (must terminate in bounds since
142     // the bitfield must have a size).
143     while (TD.getTypeStoreSizeInBits(Elts[i]->getType()) == 0)
144       ++i;
145 
146     // Promote the size of V if necessary
147     // FIXME: This should never occur, but currently it can because
148     // initializer constants are cast to bool, and because clang is
149     // not enforcing bitfield width limits.
150     if (bitFieldInfo.Size > V.getBitWidth())
151       V.zext(bitFieldInfo.Size);
152 
153     // Insert the bits into the struct
154     // FIXME: This algorthm is only correct on X86!
155     // FIXME: THis algorthm assumes bit-fields only have byte-size elements!
156     unsigned bitsToInsert = bitFieldInfo.Size;
157     unsigned curBits = std::min(8 - (fieldOffset & 7), bitsToInsert);
158     unsigned byte = V.getLoBits(curBits).getZExtValue() << (fieldOffset & 7);
159     do {
160       llvm::Constant* byteC = llvm::ConstantInt::get(llvm::Type::Int8Ty, byte);
161       Elts[i] = llvm::ConstantExpr::getOr(Elts[i], byteC);
162       ++i;
163       V = V.lshr(curBits);
164       bitsToInsert -= curBits;
165 
166       if (!bitsToInsert)
167         break;
168 
169       curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
170       byte = V.getLoBits(curBits).getZExtValue();
171     } while (true);
172   }
173 
174   llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
175     const llvm::StructType *SType =
176         cast<llvm::StructType>(ConvertType(ILE->getType()));
177     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
178     std::vector<llvm::Constant*> Elts;
179 
180     // Initialize the whole structure to zero.
181     for (unsigned i = 0; i < SType->getNumElements(); ++i) {
182       const llvm::Type *FieldTy = SType->getElementType(i);
183       Elts.push_back(llvm::Constant::getNullValue(FieldTy));
184     }
185 
186     // Copy initializer elements. Skip padding fields.
187     unsigned EltNo = 0;  // Element no in ILE
188     int FieldNo = 0; // Field no in RecordDecl
189     bool RewriteType = false;
190     for (RecordDecl::field_iterator Field = RD->field_begin(),
191                                  FieldEnd = RD->field_end();
192          EltNo < ILE->getNumInits() && Field != FieldEnd; ++Field) {
193       FieldNo++;
194       if (!Field->getIdentifier())
195         continue;
196 
197       if (Field->isBitField()) {
198         InsertBitfieldIntoStruct(Elts, *Field, ILE->getInit(EltNo));
199       } else {
200         unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(*Field);
201         llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(EltNo), CGF);
202         RewriteType |= (C->getType() != Elts[FieldNo]->getType());
203         Elts[FieldNo] = C;
204       }
205       EltNo++;
206     }
207 
208     if (RewriteType) {
209       // FIXME: Make this work for non-packed structs
210       assert(SType->isPacked() && "Cannot recreate unpacked structs");
211       std::vector<const llvm::Type*> Types;
212       for (unsigned i = 0; i < Elts.size(); ++i)
213         Types.push_back(Elts[i]->getType());
214       SType = llvm::StructType::get(Types, true);
215     }
216 
217     return llvm::ConstantStruct::get(SType, Elts);
218   }
219 
220   llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
221     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
222     const llvm::Type *Ty = ConvertType(ILE->getType());
223 
224     // Find the field decl we're initializing, if any
225     int FieldNo = 0; // Field no in RecordDecl
226     FieldDecl* curField = 0;
227     for (RecordDecl::field_iterator Field = RD->field_begin(),
228                                  FieldEnd = RD->field_end();
229          Field != FieldEnd; ++Field) {
230       curField = *Field;
231       FieldNo++;
232       if (curField->getIdentifier())
233         break;
234     }
235 
236     if (!curField || !curField->getIdentifier() || ILE->getNumInits() == 0)
237       return llvm::Constant::getNullValue(Ty);
238 
239     if (curField->isBitField()) {
240       // Create a dummy struct for bit-field insertion
241       unsigned NumElts = CGM.getTargetData().getABITypeSize(Ty) / 8;
242       llvm::Constant* NV = llvm::Constant::getNullValue(llvm::Type::Int8Ty);
243       std::vector<llvm::Constant*> Elts(NumElts, NV);
244 
245       InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
246       const llvm::ArrayType *RetTy =
247           llvm::ArrayType::get(NV->getType(), NumElts);
248       return llvm::ConstantArray::get(RetTy, Elts);
249     }
250 
251     llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(0), CGF);
252 
253     // Build a struct with the union sub-element as the first member,
254     // and padded to the appropriate size
255     std::vector<llvm::Constant*> Elts;
256     std::vector<const llvm::Type*> Types;
257     Elts.push_back(C);
258     Types.push_back(C->getType());
259     unsigned CurSize = CGM.getTargetData().getTypeStoreSize(C->getType());
260     unsigned TotalSize = CGM.getTargetData().getTypeStoreSize(Ty);
261     while (CurSize < TotalSize) {
262       Elts.push_back(llvm::Constant::getNullValue(llvm::Type::Int8Ty));
263       Types.push_back(llvm::Type::Int8Ty);
264       CurSize++;
265     }
266 
267     // This always generates a packed struct
268     // FIXME: Try to generate an unpacked struct when we can
269     llvm::StructType* STy = llvm::StructType::get(Types, true);
270     return llvm::ConstantStruct::get(STy, Elts);
271   }
272 
273   llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
274     const llvm::VectorType *VType =
275         cast<llvm::VectorType>(ConvertType(ILE->getType()));
276     const llvm::Type *ElemTy = VType->getElementType();
277     std::vector<llvm::Constant*> Elts;
278     unsigned NumElements = VType->getNumElements();
279     unsigned NumInitElements = ILE->getNumInits();
280 
281     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
282 
283     // Copy initializer elements.
284     unsigned i = 0;
285     for (; i < NumInitableElts; ++i) {
286       llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(i), CGF);
287       Elts.push_back(C);
288     }
289 
290     for (; i < NumElements; ++i)
291       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
292 
293     return llvm::ConstantVector::get(VType, Elts);
294   }
295 
296   llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
297     if (ILE->getType()->isScalarType()) {
298       // We have a scalar in braces. Just use the first element.
299       if (ILE->getNumInits() > 0)
300         return CGM.EmitConstantExpr(ILE->getInit(0), CGF);
301 
302       const llvm::Type* RetTy = CGM.getTypes().ConvertType(ILE->getType());
303       return llvm::Constant::getNullValue(RetTy);
304     }
305 
306     // FIXME: We don't codegen or sema designators yet.
307     if (ILE->hadDesignators()) {
308       CGM.ErrorUnsupported(ILE, "initializer list with designators");
309       return llvm::UndefValue::get(ConvertType(ILE->getType()));
310     }
311 
312     if (ILE->getType()->isArrayType())
313       return EmitArrayInitialization(ILE);
314 
315     if (ILE->getType()->isStructureType())
316       return EmitStructInitialization(ILE);
317 
318     if (ILE->getType()->isUnionType())
319       return EmitUnionInitialization(ILE);
320 
321     if (ILE->getType()->isVectorType())
322       return EmitVectorInitialization(ILE);
323 
324     assert(0 && "Unable to handle InitListExpr");
325     // Get rid of control reaches end of void function warning.
326     // Not reached.
327     return 0;
328   }
329 
330   llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
331     Expr* SExpr = ICExpr->getSubExpr();
332     QualType SType = SExpr->getType();
333     llvm::Constant *C; // the intermediate expression
334     QualType T;        // the type of the intermediate expression
335     if (SType->isArrayType()) {
336       // Arrays decay to a pointer to the first element
337       // VLAs would require special handling, but they can't occur here
338       C = EmitLValue(SExpr);
339       llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
340       llvm::Constant *Ops[] = {Idx0, Idx0};
341       C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
342       T = CGM.getContext().getArrayDecayedType(SType);
343     } else if (SType->isFunctionType()) {
344       // Function types decay to a pointer to the function
345       C = EmitLValue(SExpr);
346       T = CGM.getContext().getPointerType(SType);
347     } else {
348       C = Visit(SExpr);
349       T = SType;
350     }
351 
352     // Perform the conversion; note that an implicit cast can both promote
353     // and convert an array/function
354     return EmitConversion(C, T, ICExpr->getType());
355   }
356 
357   llvm::Constant *VisitStringLiteral(StringLiteral *E) {
358     assert(!E->getType()->isPointerType() && "Strings are always arrays");
359 
360     // Otherwise this must be a string initializing an array in a static
361     // initializer.  Don't emit it as the address of the string, emit the string
362     // data itself as an inline array.
363     return llvm::ConstantArray::get(CGM.GetStringForStringLiteral(E), false);
364   }
365 
366   llvm::Constant *VisitAddrLabelExpr(const AddrLabelExpr *E) {
367     assert(CGF && "Invalid address of label expression outside function.");
368     llvm::Constant *C =
369       llvm::ConstantInt::get(llvm::Type::Int32Ty,
370                              CGF->GetIDForAddrOfLabel(E->getLabel()));
371     return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
372   }
373 
374   llvm::Constant *VisitUnaryAddrOf(const UnaryOperator *E) {
375     return EmitLValue(E->getSubExpr());
376   }
377   llvm::Constant *VisitUnaryOffsetOf(const UnaryOperator *E) {
378     int64_t Val = E->evaluateOffsetOf(CGM.getContext());
379 
380     assert(E->getType()->isIntegerType() && "Result type must be an integer!");
381 
382     uint32_t ResultWidth =
383       static_cast<uint32_t>(CGM.getContext().getTypeSize(E->getType()));
384     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
385   }
386 
387   llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
388     return Visit(E->getSubExpr());
389   }
390 
391   // Binary operators
392 
393   llvm::Constant *VisitCallExpr(const CallExpr *E) {
394     Expr::EvalResult Result;
395     if (E->Evaluate(Result, CGM.getContext())) {
396       if (Result.Val.isInt())
397         return llvm::ConstantInt::get(Result.Val.getInt());
398       if (Result.Val.isFloat())
399         return llvm::ConstantFP::get(Result.Val.getFloat());
400     }
401 
402     // Handle __builtin___CFStringMakeConstantString.
403     if (E->isBuiltinCall() ==Builtin::BI__builtin___CFStringMakeConstantString){
404       const Expr *Arg = E->getArg(0)->IgnoreParenCasts();
405 
406       const StringLiteral *Literal = cast<StringLiteral>(Arg);
407       std::string S(Literal->getStrData(), Literal->getByteLength());
408       return CGM.GetAddrOfConstantCFString(S);
409     }
410 
411     CGM.ErrorUnsupported(E, "constant call expression");
412     return llvm::Constant::getNullValue(ConvertType(E->getType()));
413   }
414 
415   // Utility methods
416   const llvm::Type *ConvertType(QualType T) {
417     return CGM.getTypes().ConvertType(T);
418   }
419 
420   llvm::Constant *EmitConversionToBool(llvm::Constant *Src, QualType SrcType) {
421     assert(SrcType->isCanonical() && "EmitConversion strips typedefs");
422 
423     if (SrcType->isRealFloatingType()) {
424       // Compare against 0.0 for fp scalars.
425       llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
426       return llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UNE, Src, Zero);
427     }
428 
429     assert((SrcType->isIntegerType() || SrcType->isPointerType()) &&
430            "Unknown scalar type to convert");
431 
432     // Compare against an integer or pointer null.
433     llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
434     return llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_NE, Src, Zero);
435   }
436 
437   llvm::Constant *EmitConversion(llvm::Constant *Src, QualType SrcType,
438                                  QualType DstType) {
439     SrcType = CGM.getContext().getCanonicalType(SrcType);
440     DstType = CGM.getContext().getCanonicalType(DstType);
441     if (SrcType == DstType) return Src;
442 
443     // Handle conversions to bool first, they are special: comparisons against 0.
444     if (DstType->isBooleanType())
445       return EmitConversionToBool(Src, SrcType);
446 
447     const llvm::Type *DstTy = ConvertType(DstType);
448 
449     // Ignore conversions like int -> uint.
450     if (Src->getType() == DstTy)
451       return Src;
452 
453     // Handle pointer conversions next: pointers can only be converted to/from
454     // other pointers and integers.
455     if (isa<llvm::PointerType>(DstTy)) {
456       // The source value may be an integer, or a pointer.
457       if (isa<llvm::PointerType>(Src->getType()))
458         return llvm::ConstantExpr::getBitCast(Src, DstTy);
459       assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
460       return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
461     }
462 
463     if (isa<llvm::PointerType>(Src->getType())) {
464       // Must be an ptr to int cast.
465       assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
466       return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
467     }
468 
469     // A scalar source can be splatted to a vector of the same element type
470     if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
471       assert((cast<llvm::VectorType>(DstTy)->getElementType()
472               == Src->getType()) &&
473              "Vector element type must match scalar type to splat.");
474       unsigned NumElements = DstType->getAsVectorType()->getNumElements();
475       llvm::SmallVector<llvm::Constant*, 16> Elements;
476       for (unsigned i = 0; i < NumElements; i++)
477         Elements.push_back(Src);
478 
479       return llvm::ConstantVector::get(&Elements[0], NumElements);
480     }
481 
482     if (isa<llvm::VectorType>(Src->getType()) ||
483         isa<llvm::VectorType>(DstTy)) {
484       return llvm::ConstantExpr::getBitCast(Src, DstTy);
485     }
486 
487     // Finally, we have the arithmetic types: real int/float.
488     if (isa<llvm::IntegerType>(Src->getType())) {
489       bool InputSigned = SrcType->isSignedIntegerType();
490       if (isa<llvm::IntegerType>(DstTy))
491         return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
492       else if (InputSigned)
493         return llvm::ConstantExpr::getSIToFP(Src, DstTy);
494       else
495         return llvm::ConstantExpr::getUIToFP(Src, DstTy);
496     }
497 
498     assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
499     if (isa<llvm::IntegerType>(DstTy)) {
500       if (DstType->isSignedIntegerType())
501         return llvm::ConstantExpr::getFPToSI(Src, DstTy);
502       else
503         return llvm::ConstantExpr::getFPToUI(Src, DstTy);
504     }
505 
506     assert(DstTy->isFloatingPoint() && "Unknown real conversion");
507     if (DstTy->getTypeID() < Src->getType()->getTypeID())
508       return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
509     else
510       return llvm::ConstantExpr::getFPExtend(Src, DstTy);
511   }
512 
513   llvm::Constant *EmitSizeAlignOf(QualType TypeToSize,
514                                   QualType RetType, bool isSizeOf) {
515     std::pair<uint64_t, unsigned> Info =
516       CGM.getContext().getTypeInfo(TypeToSize);
517 
518     uint64_t Val = isSizeOf ? Info.first : Info.second;
519     Val /= 8;  // Return size in bytes, not bits.
520 
521     assert(RetType->isIntegerType() && "Result type must be an integer!");
522 
523     uint32_t ResultWidth =
524       static_cast<uint32_t>(CGM.getContext().getTypeSize(RetType));
525     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
526   }
527 
528 public:
529   llvm::Constant *EmitLValue(Expr *E) {
530     switch (E->getStmtClass()) {
531     default: break;
532     case Expr::ParenExprClass:
533       // Elide parenthesis
534       return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
535     case Expr::CompoundLiteralExprClass: {
536       // Note that due to the nature of compound literals, this is guaranteed
537       // to be the only use of the variable, so we just generate it here.
538       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
539       llvm::Constant* C = Visit(CLE->getInitializer());
540       C = new llvm::GlobalVariable(C->getType(),E->getType().isConstQualified(),
541                                    llvm::GlobalValue::InternalLinkage,
542                                    C, ".compoundliteral", &CGM.getModule());
543       return C;
544     }
545     case Expr::DeclRefExprClass: {
546       NamedDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
547       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
548         return CGM.GetAddrOfFunction(FD);
549       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
550         if (VD->isFileVarDecl())
551           return CGM.GetAddrOfGlobalVar(VD);
552         else if (VD->isBlockVarDecl()) {
553           assert(CGF && "Can't access static local vars without CGF");
554           return CGF->GetAddrOfStaticLocalVar(VD);
555         }
556       }
557       break;
558     }
559     case Expr::MemberExprClass: {
560       MemberExpr* ME = cast<MemberExpr>(E);
561       llvm::Constant *Base;
562       if (ME->isArrow())
563         Base = Visit(ME->getBase());
564       else
565         Base = EmitLValue(ME->getBase());
566 
567       FieldDecl *Field = dyn_cast<FieldDecl>(ME->getMemberDecl());
568       // FIXME: Handle other kinds of member expressions.
569       assert(Field && "No code generation for non-field member expressions");
570       unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(Field);
571       llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
572       llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
573                                                    FieldNumber);
574       llvm::Value *Ops[] = {Zero, Idx};
575       return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
576     }
577     case Expr::ArraySubscriptExprClass: {
578       ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
579       llvm::Constant *Base = Visit(ASExpr->getBase());
580       llvm::Constant *Index = Visit(ASExpr->getIdx());
581       assert(!ASExpr->getBase()->getType()->isVectorType() &&
582              "Taking the address of a vector component is illegal!");
583       return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
584     }
585     case Expr::StringLiteralClass:
586       return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
587     case Expr::ObjCStringLiteralClass: {
588       ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
589       std::string S(SL->getString()->getStrData(),
590                     SL->getString()->getByteLength());
591       llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(S);
592       return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
593     }
594     case Expr::UnaryOperatorClass: {
595       UnaryOperator *Exp = cast<UnaryOperator>(E);
596       switch (Exp->getOpcode()) {
597       default: break;
598       case UnaryOperator::Extension:
599         // Extension is just a wrapper for expressions
600         return EmitLValue(Exp->getSubExpr());
601       case UnaryOperator::Real:
602       case UnaryOperator::Imag: {
603         // The address of __real or __imag is just a GEP off the address
604         // of the internal expression
605         llvm::Constant* C = EmitLValue(Exp->getSubExpr());
606         llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
607         llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
608                                        Exp->getOpcode() == UnaryOperator::Imag);
609         llvm::Value *Ops[] = {Zero, Idx};
610         return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
611       }
612       case UnaryOperator::Deref:
613         // The address of a deref is just the value of the expression
614         return Visit(Exp->getSubExpr());
615       }
616       break;
617     }
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     }
629     CGM.ErrorUnsupported(E, "constant l-value expression");
630     llvm::Type *Ty = llvm::PointerType::getUnqual(ConvertType(E->getType()));
631     return llvm::UndefValue::get(Ty);
632   }
633 };
634 
635 }  // end anonymous namespace.
636 
637 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
638                                                 CodeGenFunction *CGF) {
639   QualType type = Context.getCanonicalType(E->getType());
640 
641   Expr::EvalResult Result;
642 
643   if (E->Evaluate(Result, Context)) {
644     assert(!Result.HasSideEffects &&
645            "Constant expr should not have any side effects!");
646     switch (Result.Val.getKind()) {
647     default: assert(0 && "unhandled value kind!");
648     case APValue::LValue: {
649       llvm::Constant *Offset =
650         llvm::ConstantInt::get(llvm::Type::Int64Ty,
651                                Result.Val.getLValueOffset());
652 
653       if (const Expr *LVBase = Result.Val.getLValueBase()) {
654         llvm::Constant *C =
655           ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
656 
657         const llvm::Type *Type =
658           llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
659         const llvm::Type *DestType = getTypes().ConvertTypeForMem(E->getType());
660 
661         // FIXME: It's a little ugly that we need to cast to a pointer,
662         // apply the GEP and then cast back.
663         C = llvm::ConstantExpr::getBitCast(C, Type);
664         C = llvm::ConstantExpr::getGetElementPtr(C, &Offset, 1);
665 
666         return llvm::ConstantExpr::getBitCast(C, DestType);
667       }
668 
669       return llvm::ConstantExpr::getIntToPtr(Offset,
670                                              getTypes().ConvertType(type));
671     }
672     case APValue::Int: {
673       llvm::Constant *C = llvm::ConstantInt::get(Result.Val.getInt());
674 
675       if (C->getType() == llvm::Type::Int1Ty) {
676         const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
677         C = llvm::ConstantExpr::getZExt(C, BoolTy);
678       }
679       return C;
680     }
681     case APValue::Float:
682       return llvm::ConstantFP::get(Result.Val.getFloat());
683     case APValue::ComplexFloat: {
684       llvm::Constant *Complex[2];
685 
686       Complex[0] = llvm::ConstantFP::get(Result.Val.getComplexFloatReal());
687       Complex[1] = llvm::ConstantFP::get(Result.Val.getComplexFloatImag());
688 
689       return llvm::ConstantStruct::get(Complex, 2);
690     }
691     }
692   }
693 
694   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
695   if (C->getType() == llvm::Type::Int1Ty) {
696     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
697     C = llvm::ConstantExpr::getZExt(C, BoolTy);
698   }
699   return C;
700 }
701