CGExprConstant.cpp revision 34e7946831a63f96d3ba3478c74ca8e25ee52d7e 
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"
25using namespace clang;
26using namespace CodeGen;
27
28namespace  {
29class VISIBILITY_HIDDEN ConstExprEmitter :
30  public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
31  CodeGenModule &CGM;
32  CodeGenFunction *CGF;
33public:
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
475public:
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
600llvm::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