CGExprConstant.cpp revision b83d287bc7f47d36fb0751a481e2ef9308b37252 
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    return EmitConversion(C, E->getSubExpr()->getType(), E->getType());
65  }
66
67  llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
68    return Visit(DAE->getExpr());
69  }
70
71  llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
72    std::vector<llvm::Constant*> Elts;
73    const llvm::ArrayType *AType =
74        cast<llvm::ArrayType>(ConvertType(ILE->getType()));
75    unsigned NumInitElements = ILE->getNumInits();
76    // FIXME: Check for wide strings
77    if (NumInitElements > 0 && isa<StringLiteral>(ILE->getInit(0)) &&
78        ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
79      return Visit(ILE->getInit(0));
80    const llvm::Type *ElemTy = AType->getElementType();
81    unsigned NumElements = AType->getNumElements();
82
83    // Initialising an array requires us to automatically
84    // initialise any elements that have not been initialised explicitly
85    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
86
87    // Copy initializer elements.
88    unsigned i = 0;
89    bool RewriteType = false;
90    for (; i < NumInitableElts; ++i) {
91      llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(i), CGF);
92      if (!C)
93        return 0;
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    if (!C)
119      return;
120
121    llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
122    if (!CI) {
123      CGM.ErrorUnsupported(E, "bitfield initialization");
124      return;
125    }
126    llvm::APInt V = CI->getValue();
127
128    // Calculate information about the relevant field
129    const llvm::Type* Ty = CI->getType();
130    const llvm::TargetData &TD = CGM.getTypes().getTargetData();
131    unsigned size = TD.getTypePaddedSizeInBits(Ty);
132    unsigned fieldOffset = CGM.getTypes().getLLVMFieldNo(Field) * size;
133    CodeGenTypes::BitFieldInfo bitFieldInfo =
134        CGM.getTypes().getBitFieldInfo(Field);
135    fieldOffset += bitFieldInfo.Begin;
136
137    // Find where to start the insertion
138    // FIXME: This is O(n^2) in the number of bit-fields!
139    // FIXME: This won't work if the struct isn't completely packed!
140    unsigned offset = 0, i = 0;
141    while (offset < (fieldOffset & -8))
142      offset += TD.getTypePaddedSizeInBits(Elts[i++]->getType());
143
144    // Advance over 0 sized elements (must terminate in bounds since
145    // the bitfield must have a size).
146    while (TD.getTypePaddedSizeInBits(Elts[i]->getType()) == 0)
147      ++i;
148
149    // Promote the size of V if necessary
150    // FIXME: This should never occur, but currently it can because
151    // initializer constants are cast to bool, and because clang is
152    // not enforcing bitfield width limits.
153    if (bitFieldInfo.Size > V.getBitWidth())
154      V.zext(bitFieldInfo.Size);
155
156    // Insert the bits into the struct
157    // FIXME: This algorthm is only correct on X86!
158    // FIXME: THis algorthm assumes bit-fields only have byte-size elements!
159    unsigned bitsToInsert = bitFieldInfo.Size;
160    unsigned curBits = std::min(8 - (fieldOffset & 7), bitsToInsert);
161    unsigned byte = V.getLoBits(curBits).getZExtValue() << (fieldOffset & 7);
162    do {
163      llvm::Constant* byteC = llvm::ConstantInt::get(llvm::Type::Int8Ty, byte);
164      Elts[i] = llvm::ConstantExpr::getOr(Elts[i], byteC);
165      ++i;
166      V = V.lshr(curBits);
167      bitsToInsert -= curBits;
168
169      if (!bitsToInsert)
170        break;
171
172      curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
173      byte = V.getLoBits(curBits).getZExtValue();
174    } while (true);
175  }
176
177  llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
178    const llvm::StructType *SType =
179        cast<llvm::StructType>(ConvertType(ILE->getType()));
180    RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
181    std::vector<llvm::Constant*> Elts;
182
183    // Initialize the whole structure to zero.
184    for (unsigned i = 0; i < SType->getNumElements(); ++i) {
185      const llvm::Type *FieldTy = SType->getElementType(i);
186      Elts.push_back(llvm::Constant::getNullValue(FieldTy));
187    }
188
189    // Copy initializer elements. Skip padding fields.
190    unsigned EltNo = 0;  // Element no in ILE
191    int FieldNo = 0; // Field no in RecordDecl
192    bool RewriteType = false;
193    for (RecordDecl::field_iterator Field = RD->field_begin(),
194                                 FieldEnd = RD->field_end();
195         EltNo < ILE->getNumInits() && Field != FieldEnd; ++Field) {
196      FieldNo++;
197      if (!Field->getIdentifier())
198        continue;
199
200      if (Field->isBitField()) {
201        InsertBitfieldIntoStruct(Elts, *Field, ILE->getInit(EltNo));
202      } else {
203        unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(*Field);
204        llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(EltNo), CGF);
205        if (!C) return 0;
206        RewriteType |= (C->getType() != Elts[FieldNo]->getType());
207        Elts[FieldNo] = C;
208      }
209      EltNo++;
210    }
211
212    if (RewriteType) {
213      // FIXME: Make this work for non-packed structs
214      assert(SType->isPacked() && "Cannot recreate unpacked structs");
215      std::vector<const llvm::Type*> Types;
216      for (unsigned i = 0; i < Elts.size(); ++i)
217        Types.push_back(Elts[i]->getType());
218      SType = llvm::StructType::get(Types, true);
219    }
220
221    return llvm::ConstantStruct::get(SType, Elts);
222  }
223
224  llvm::Constant *EmitUnion(llvm::Constant *C, const llvm::Type *Ty) {
225    if (!C)
226      return 0;
227
228    // Build a struct with the union sub-element as the first member,
229    // and padded to the appropriate size
230    std::vector<llvm::Constant*> Elts;
231    std::vector<const llvm::Type*> Types;
232    Elts.push_back(C);
233    Types.push_back(C->getType());
234    unsigned CurSize = CGM.getTargetData().getTypePaddedSize(C->getType());
235    unsigned TotalSize = CGM.getTargetData().getTypePaddedSize(Ty);
236    while (CurSize < TotalSize) {
237      Elts.push_back(llvm::Constant::getNullValue(llvm::Type::Int8Ty));
238      Types.push_back(llvm::Type::Int8Ty);
239      CurSize++;
240    }
241
242    // This always generates a packed struct
243    // FIXME: Try to generate an unpacked struct when we can
244    llvm::StructType* STy = llvm::StructType::get(Types, true);
245    return llvm::ConstantStruct::get(STy, Elts);
246  }
247
248  llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
249    const llvm::Type *Ty = ConvertType(ILE->getType());
250
251    // If this is an empty initializer list, we value-initialize the
252    // union.
253    if (ILE->getNumInits() == 0)
254      return llvm::Constant::getNullValue(Ty);
255
256    FieldDecl* curField = ILE->getInitializedFieldInUnion();
257    if (!curField) {
258      // There's no field to initialize, so value-initialize the union.
259#ifndef NDEBUG
260      // Make sure that it's really an empty and not a failure of
261      // semantic analysis.
262      RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
263      for (RecordDecl::field_iterator Field = RD->field_begin(),
264                                   FieldEnd = RD->field_end();
265           Field != FieldEnd; ++Field)
266        assert(Field->isUnnamedBitfield() && "Only unnamed bitfields allowed");
267#endif
268      return llvm::Constant::getNullValue(Ty);
269    }
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      if (!C)
301        return 0;
302      Elts.push_back(C);
303    }
304
305    for (; i < NumElements; ++i)
306      Elts.push_back(llvm::Constant::getNullValue(ElemTy));
307
308    return llvm::ConstantVector::get(VType, Elts);
309  }
310
311  llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
312    const llvm::Type* RetTy = CGM.getTypes().ConvertType(E->getType());
313    return llvm::Constant::getNullValue(RetTy);
314  }
315
316  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
317    if (ILE->getType()->isScalarType()) {
318      // We have a scalar in braces. Just use the first element.
319      if (ILE->getNumInits() > 0)
320        return CGM.EmitConstantExpr(ILE->getInit(0), CGF);
321
322      const llvm::Type* RetTy = CGM.getTypes().ConvertType(ILE->getType());
323      return llvm::Constant::getNullValue(RetTy);
324    }
325
326    if (ILE->getType()->isArrayType())
327      return EmitArrayInitialization(ILE);
328
329    if (ILE->getType()->isStructureType())
330      return EmitStructInitialization(ILE);
331
332    if (ILE->getType()->isUnionType())
333      return EmitUnionInitialization(ILE);
334
335    if (ILE->getType()->isVectorType())
336      return EmitVectorInitialization(ILE);
337
338    assert(0 && "Unable to handle InitListExpr");
339    // Get rid of control reaches end of void function warning.
340    // Not reached.
341    return 0;
342  }
343
344  llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
345    Expr* SExpr = ICExpr->getSubExpr();
346    QualType SType = SExpr->getType();
347    llvm::Constant *C; // the intermediate expression
348    QualType T;        // the type of the intermediate expression
349    if (SType->isArrayType()) {
350      // Arrays decay to a pointer to the first element
351      // VLAs would require special handling, but they can't occur here
352      C = EmitLValue(SExpr);
353      llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
354      llvm::Constant *Ops[] = {Idx0, Idx0};
355      C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
356      T = CGM.getContext().getArrayDecayedType(SType);
357    } else if (SType->isFunctionType()) {
358      // Function types decay to a pointer to the function
359      C = EmitLValue(SExpr);
360      T = CGM.getContext().getPointerType(SType);
361    } else {
362      C = Visit(SExpr);
363      T = SType;
364    }
365
366    // Perform the conversion; note that an implicit cast can both promote
367    // and convert an array/function
368    return EmitConversion(C, T, ICExpr->getType());
369  }
370
371  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
372    assert(!E->getType()->isPointerType() && "Strings are always arrays");
373
374    // Otherwise this must be a string initializing an array in a static
375    // initializer.  Don't emit it as the address of the string, emit the string
376    // data itself as an inline array.
377    return llvm::ConstantArray::get(CGM.GetStringForStringLiteral(E), false);
378  }
379
380  llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
381    return Visit(E->getSubExpr());
382  }
383
384  llvm::Constant *VisitBlockExpr(const BlockExpr *E) {
385    assert (!E->hasBlockDeclRefExprs() && "global block with BlockDeclRefs");
386
387    const char *Name = "";
388    if (const NamedDecl *ND = dyn_cast<NamedDecl>(CGF->CurFuncDecl))
389      Name = ND->getNameAsString().c_str();
390    return CGM.GetAddrOfGlobalBlock(E, Name);
391  }
392
393  // Utility methods
394  const llvm::Type *ConvertType(QualType T) {
395    return CGM.getTypes().ConvertType(T);
396  }
397
398  llvm::Constant *EmitConversionToBool(llvm::Constant *Src, QualType SrcType) {
399    assert(SrcType->isCanonical() && "EmitConversion strips typedefs");
400
401    if (SrcType->isRealFloatingType()) {
402      // Compare against 0.0 for fp scalars.
403      llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
404      return llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UNE, Src, Zero);
405    }
406
407    assert((SrcType->isIntegerType() || SrcType->isPointerType()) &&
408           "Unknown scalar type to convert");
409
410    // Compare against an integer or pointer null.
411    llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
412    return llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_NE, Src, Zero);
413  }
414
415  llvm::Constant *EmitConversion(llvm::Constant *Src, QualType SrcType,
416                                 QualType DstType) {
417    if (!Src)
418      return 0;
419
420    SrcType = CGM.getContext().getCanonicalType(SrcType);
421    DstType = CGM.getContext().getCanonicalType(DstType);
422    if (SrcType == DstType) return Src;
423
424    // Handle conversions to bool first, they are special: comparisons against 0.
425    if (DstType->isBooleanType())
426      return EmitConversionToBool(Src, SrcType);
427
428    const llvm::Type *DstTy = ConvertType(DstType);
429
430    // Ignore conversions like int -> uint.
431    if (Src->getType() == DstTy)
432      return Src;
433
434    // Handle pointer conversions next: pointers can only be converted to/from
435    // other pointers and integers.
436    if (isa<llvm::PointerType>(DstTy)) {
437      // The source value may be an integer, or a pointer.
438      if (isa<llvm::PointerType>(Src->getType()))
439        return llvm::ConstantExpr::getBitCast(Src, DstTy);
440      assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
441      return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
442    }
443
444    if (isa<llvm::PointerType>(Src->getType())) {
445      // Must be an ptr to int cast.
446      assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
447      return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
448    }
449
450    // A scalar source can be splatted to a vector of the same element type
451    if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
452      assert((cast<llvm::VectorType>(DstTy)->getElementType()
453              == Src->getType()) &&
454             "Vector element type must match scalar type to splat.");
455      unsigned NumElements = DstType->getAsVectorType()->getNumElements();
456      llvm::SmallVector<llvm::Constant*, 16> Elements;
457      for (unsigned i = 0; i < NumElements; i++)
458        Elements.push_back(Src);
459
460      return llvm::ConstantVector::get(&Elements[0], NumElements);
461    }
462
463    if (isa<llvm::VectorType>(Src->getType()) ||
464        isa<llvm::VectorType>(DstTy)) {
465      return llvm::ConstantExpr::getBitCast(Src, DstTy);
466    }
467
468    // Finally, we have the arithmetic types: real int/float.
469    if (isa<llvm::IntegerType>(Src->getType())) {
470      bool InputSigned = SrcType->isSignedIntegerType();
471      if (isa<llvm::IntegerType>(DstTy))
472        return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
473      else if (InputSigned)
474        return llvm::ConstantExpr::getSIToFP(Src, DstTy);
475      else
476        return llvm::ConstantExpr::getUIToFP(Src, DstTy);
477    }
478
479    assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
480    if (isa<llvm::IntegerType>(DstTy)) {
481      if (DstType->isSignedIntegerType())
482        return llvm::ConstantExpr::getFPToSI(Src, DstTy);
483      else
484        return llvm::ConstantExpr::getFPToUI(Src, DstTy);
485    }
486
487    assert(DstTy->isFloatingPoint() && "Unknown real conversion");
488    if (DstTy->getTypeID() < Src->getType()->getTypeID())
489      return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
490    else
491      return llvm::ConstantExpr::getFPExtend(Src, DstTy);
492  }
493
494public:
495  llvm::Constant *EmitLValue(Expr *E) {
496    switch (E->getStmtClass()) {
497    default: break;
498    case Expr::ParenExprClass:
499      // Elide parenthesis
500      return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
501    case Expr::CompoundLiteralExprClass: {
502      // Note that due to the nature of compound literals, this is guaranteed
503      // to be the only use of the variable, so we just generate it here.
504      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
505      llvm::Constant* C = Visit(CLE->getInitializer());
506      // FIXME: "Leaked" on failure.
507      if (C)
508        C = new llvm::GlobalVariable(C->getType(),
509                                     E->getType().isConstQualified(),
510                                     llvm::GlobalValue::InternalLinkage,
511                                     C, ".compoundliteral", &CGM.getModule());
512      return C;
513    }
514    case Expr::DeclRefExprClass:
515    case Expr::QualifiedDeclRefExprClass: {
516      NamedDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
517      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
518        return CGM.GetAddrOfFunction(FD);
519      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
520        if (VD->isFileVarDecl())
521          return CGM.GetAddrOfGlobalVar(VD);
522        else if (VD->isBlockVarDecl()) {
523          assert(CGF && "Can't access static local vars without CGF");
524          return CGF->GetAddrOfStaticLocalVar(VD);
525        }
526      }
527      break;
528    }
529    case Expr::MemberExprClass: {
530      MemberExpr* ME = cast<MemberExpr>(E);
531      llvm::Constant *Base;
532      if (ME->isArrow())
533        Base = Visit(ME->getBase());
534      else
535        Base = EmitLValue(ME->getBase());
536      if (!Base)
537        return 0;
538
539      FieldDecl *Field = dyn_cast<FieldDecl>(ME->getMemberDecl());
540      // FIXME: Handle other kinds of member expressions.
541      assert(Field && "No code generation for non-field member expressions");
542      unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(Field);
543      llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
544      llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
545                                                   FieldNumber);
546      llvm::Value *Ops[] = {Zero, Idx};
547      return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
548    }
549    case Expr::ArraySubscriptExprClass: {
550      ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
551      assert(!ASExpr->getBase()->getType()->isVectorType() &&
552             "Taking the address of a vector component is illegal!");
553
554      llvm::Constant *Base = Visit(ASExpr->getBase());
555      llvm::Constant *Index = Visit(ASExpr->getIdx());
556      if (!Base || !Index)
557        return 0;
558      return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
559    }
560    case Expr::StringLiteralClass:
561      return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
562    case Expr::ObjCStringLiteralClass: {
563      ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
564      std::string S(SL->getString()->getStrData(),
565                    SL->getString()->getByteLength());
566      llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(S);
567      return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
568    }
569    case Expr::UnaryOperatorClass: {
570      UnaryOperator *Exp = cast<UnaryOperator>(E);
571      switch (Exp->getOpcode()) {
572      default: break;
573      case UnaryOperator::Extension:
574        // Extension is just a wrapper for expressions
575        return EmitLValue(Exp->getSubExpr());
576      case UnaryOperator::Real:
577      case UnaryOperator::Imag: {
578        // The address of __real or __imag is just a GEP off the address
579        // of the internal expression
580        llvm::Constant* C = EmitLValue(Exp->getSubExpr());
581        llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
582        llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
583                                       Exp->getOpcode() == UnaryOperator::Imag);
584        llvm::Value *Ops[] = {Zero, Idx};
585        return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
586      }
587      case UnaryOperator::Deref:
588        // The address of a deref is just the value of the expression
589        return Visit(Exp->getSubExpr());
590      }
591      break;
592    }
593
594    case Expr::PredefinedExprClass: {
595      // __func__/__FUNCTION__ -> "".  __PRETTY_FUNCTION__ -> "top level".
596      std::string Str;
597      if (cast<PredefinedExpr>(E)->getIdentType() ==
598          PredefinedExpr::PrettyFunction)
599        Str = "top level";
600
601      return CGM.GetAddrOfConstantCString(Str, ".tmp");
602    }
603    case Expr::AddrLabelExprClass: {
604      assert(CGF && "Invalid address of label expression outside function.");
605      unsigned id = CGF->GetIDForAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
606      llvm::Constant *C = llvm::ConstantInt::get(llvm::Type::Int32Ty, id);
607      return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
608    }
609    case Expr::CallExprClass: {
610      CallExpr* CE = cast<CallExpr>(E);
611      if (CE->isBuiltinCall(CGM.getContext()) !=
612            Builtin::BI__builtin___CFStringMakeConstantString)
613        break;
614      const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
615      const StringLiteral *Literal = cast<StringLiteral>(Arg);
616      std::string S(Literal->getStrData(), Literal->getByteLength());
617      return CGM.GetAddrOfConstantCFString(S);
618    }
619    case Expr::BlockExprClass: {
620      BlockExpr *B = cast<BlockExpr>(E);
621      if (!B->hasBlockDeclRefExprs())
622        return CGF->BuildBlockLiteralTmp(B);
623    }
624    }
625
626    return 0;
627  }
628};
629
630}  // end anonymous namespace.
631
632llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
633                                                CodeGenFunction *CGF) {
634  Expr::EvalResult Result;
635
636  if (E->Evaluate(Result, Context)) {
637    assert(!Result.HasSideEffects &&
638           "Constant expr should not have any side effects!");
639    switch (Result.Val.getKind()) {
640    case APValue::Uninitialized:
641      assert(0 && "Constant expressions should be initialized.");
642      return 0;
643    case APValue::LValue: {
644      const llvm::Type *DestType = getTypes().ConvertTypeForMem(E->getType());
645      llvm::Constant *Offset =
646        llvm::ConstantInt::get(llvm::Type::Int64Ty,
647                               Result.Val.getLValueOffset());
648
649      llvm::Constant *C;
650      if (const Expr *LVBase = Result.Val.getLValueBase()) {
651        C = ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
652
653        // Apply offset if necessary.
654        if (!Offset->isNullValue()) {
655          const llvm::Type *Type =
656            llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
657          llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
658          Casted = llvm::ConstantExpr::getGetElementPtr(Casted, &Offset, 1);
659          C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
660        }
661
662        // Convert to the appropriate type; this could be an lvalue for
663        // an integer.
664        if (isa<llvm::PointerType>(DestType))
665          return llvm::ConstantExpr::getBitCast(C, DestType);
666
667        return llvm::ConstantExpr::getPtrToInt(C, DestType);
668      } else {
669        C = Offset;
670
671        // Convert to the appropriate type; this could be an lvalue for
672        // an integer.
673        if (isa<llvm::PointerType>(DestType))
674          return llvm::ConstantExpr::getIntToPtr(C, DestType);
675
676        // If the types don't match this should only be a truncate.
677        if (C->getType() != DestType)
678          return llvm::ConstantExpr::getTrunc(C, DestType);
679
680        return C;
681      }
682    }
683    case APValue::Int: {
684      llvm::Constant *C = llvm::ConstantInt::get(Result.Val.getInt());
685
686      if (C->getType() == llvm::Type::Int1Ty) {
687        const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
688        C = llvm::ConstantExpr::getZExt(C, BoolTy);
689      }
690      return C;
691    }
692    case APValue::ComplexInt: {
693      llvm::Constant *Complex[2];
694
695      Complex[0] = llvm::ConstantInt::get(Result.Val.getComplexIntReal());
696      Complex[1] = llvm::ConstantInt::get(Result.Val.getComplexIntImag());
697
698      return llvm::ConstantStruct::get(Complex, 2);
699    }
700    case APValue::Float:
701      return llvm::ConstantFP::get(Result.Val.getFloat());
702    case APValue::ComplexFloat: {
703      llvm::Constant *Complex[2];
704
705      Complex[0] = llvm::ConstantFP::get(Result.Val.getComplexFloatReal());
706      Complex[1] = llvm::ConstantFP::get(Result.Val.getComplexFloatImag());
707
708      return llvm::ConstantStruct::get(Complex, 2);
709    }
710    case APValue::Vector: {
711      llvm::SmallVector<llvm::Constant *, 4> Inits;
712      unsigned NumElts = Result.Val.getVectorLength();
713
714      for (unsigned i = 0; i != NumElts; ++i) {
715        APValue &Elt = Result.Val.getVectorElt(i);
716        if (Elt.isInt())
717          Inits.push_back(llvm::ConstantInt::get(Elt.getInt()));
718        else
719          Inits.push_back(llvm::ConstantFP::get(Elt.getFloat()));
720      }
721      return llvm::ConstantVector::get(&Inits[0], Inits.size());
722    }
723    }
724  }
725
726  llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
727  if (C && C->getType() == llvm::Type::Int1Ty) {
728    const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
729    C = llvm::ConstantExpr::getZExt(C, BoolTy);
730  }
731  return C;
732}
733