CGExprConstant.cpp revision 7d801eae4db97c46e47c40d431d34225ce6f6143 
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    // If this is an empty initializer list, we value-initialize the
245    // union.
246    if (ILE->getNumInits() == 0)
247      return llvm::Constant::getNullValue(Ty);
248
249    FieldDecl* curField = ILE->getInitializedFieldInUnion();
250    if (!curField) {
251      // There's no field to initialize, so value-initialize the union.
252#ifndef NDEBUG
253      // Make sure that it's really an empty and not a failure of
254      // semantic analysis.
255      for (RecordDecl::field_iterator Field = RD->field_begin(),
256                                   FieldEnd = RD->field_end();
257           Field != FieldEnd; ++Field)
258        assert(Field->isUnnamedBitfield() && "Only unnamed bitfields allowed");
259#endif
260      return llvm::Constant::getNullValue(Ty);
261    }
262
263    if (curField->isBitField()) {
264      // Create a dummy struct for bit-field insertion
265      unsigned NumElts = CGM.getTargetData().getTypePaddedSize(Ty) / 8;
266      llvm::Constant* NV = llvm::Constant::getNullValue(llvm::Type::Int8Ty);
267      std::vector<llvm::Constant*> Elts(NumElts, NV);
268
269      InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
270      const llvm::ArrayType *RetTy =
271          llvm::ArrayType::get(NV->getType(), NumElts);
272      return llvm::ConstantArray::get(RetTy, Elts);
273    }
274
275    return EmitUnion(CGM.EmitConstantExpr(ILE->getInit(0), CGF), Ty);
276  }
277
278  llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
279    const llvm::VectorType *VType =
280        cast<llvm::VectorType>(ConvertType(ILE->getType()));
281    const llvm::Type *ElemTy = VType->getElementType();
282    std::vector<llvm::Constant*> Elts;
283    unsigned NumElements = VType->getNumElements();
284    unsigned NumInitElements = ILE->getNumInits();
285
286    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
287
288    // Copy initializer elements.
289    unsigned i = 0;
290    for (; i < NumInitableElts; ++i) {
291      llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(i), CGF);
292      Elts.push_back(C);
293    }
294
295    for (; i < NumElements; ++i)
296      Elts.push_back(llvm::Constant::getNullValue(ElemTy));
297
298    return llvm::ConstantVector::get(VType, Elts);
299  }
300
301  llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
302    const llvm::Type* RetTy = CGM.getTypes().ConvertType(E->getType());
303    return llvm::Constant::getNullValue(RetTy);
304  }
305
306  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
307    if (ILE->getType()->isScalarType()) {
308      // We have a scalar in braces. Just use the first element.
309      if (ILE->getNumInits() > 0)
310        return CGM.EmitConstantExpr(ILE->getInit(0), CGF);
311
312      const llvm::Type* RetTy = CGM.getTypes().ConvertType(ILE->getType());
313      return llvm::Constant::getNullValue(RetTy);
314    }
315
316    if (ILE->getType()->isArrayType())
317      return EmitArrayInitialization(ILE);
318
319    if (ILE->getType()->isStructureType())
320      return EmitStructInitialization(ILE);
321
322    if (ILE->getType()->isUnionType())
323      return EmitUnionInitialization(ILE);
324
325    if (ILE->getType()->isVectorType())
326      return EmitVectorInitialization(ILE);
327
328    assert(0 && "Unable to handle InitListExpr");
329    // Get rid of control reaches end of void function warning.
330    // Not reached.
331    return 0;
332  }
333
334  llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
335    Expr* SExpr = ICExpr->getSubExpr();
336    QualType SType = SExpr->getType();
337    llvm::Constant *C; // the intermediate expression
338    QualType T;        // the type of the intermediate expression
339    if (SType->isArrayType()) {
340      // Arrays decay to a pointer to the first element
341      // VLAs would require special handling, but they can't occur here
342      C = EmitLValue(SExpr);
343      llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
344      llvm::Constant *Ops[] = {Idx0, Idx0};
345      C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
346      T = CGM.getContext().getArrayDecayedType(SType);
347    } else if (SType->isFunctionType()) {
348      // Function types decay to a pointer to the function
349      C = EmitLValue(SExpr);
350      T = CGM.getContext().getPointerType(SType);
351    } else {
352      C = Visit(SExpr);
353      T = SType;
354    }
355
356    // Perform the conversion; note that an implicit cast can both promote
357    // and convert an array/function
358    return EmitConversion(C, T, ICExpr->getType());
359  }
360
361  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
362    assert(!E->getType()->isPointerType() && "Strings are always arrays");
363
364    // Otherwise this must be a string initializing an array in a static
365    // initializer.  Don't emit it as the address of the string, emit the string
366    // data itself as an inline array.
367    return llvm::ConstantArray::get(CGM.GetStringForStringLiteral(E), false);
368  }
369
370  llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
371    return Visit(E->getSubExpr());
372  }
373
374  // Utility methods
375  const llvm::Type *ConvertType(QualType T) {
376    return CGM.getTypes().ConvertType(T);
377  }
378
379  llvm::Constant *EmitConversionToBool(llvm::Constant *Src, QualType SrcType) {
380    assert(SrcType->isCanonical() && "EmitConversion strips typedefs");
381
382    if (SrcType->isRealFloatingType()) {
383      // Compare against 0.0 for fp scalars.
384      llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
385      return llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UNE, Src, Zero);
386    }
387
388    assert((SrcType->isIntegerType() || SrcType->isPointerType()) &&
389           "Unknown scalar type to convert");
390
391    // Compare against an integer or pointer null.
392    llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
393    return llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_NE, Src, Zero);
394  }
395
396  llvm::Constant *EmitConversion(llvm::Constant *Src, QualType SrcType,
397                                 QualType DstType) {
398    SrcType = CGM.getContext().getCanonicalType(SrcType);
399    DstType = CGM.getContext().getCanonicalType(DstType);
400    if (SrcType == DstType) return Src;
401
402    // Handle conversions to bool first, they are special: comparisons against 0.
403    if (DstType->isBooleanType())
404      return EmitConversionToBool(Src, SrcType);
405
406    const llvm::Type *DstTy = ConvertType(DstType);
407
408    // Ignore conversions like int -> uint.
409    if (Src->getType() == DstTy)
410      return Src;
411
412    // Handle pointer conversions next: pointers can only be converted to/from
413    // other pointers and integers.
414    if (isa<llvm::PointerType>(DstTy)) {
415      // The source value may be an integer, or a pointer.
416      if (isa<llvm::PointerType>(Src->getType()))
417        return llvm::ConstantExpr::getBitCast(Src, DstTy);
418      assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
419      return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
420    }
421
422    if (isa<llvm::PointerType>(Src->getType())) {
423      // Must be an ptr to int cast.
424      assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
425      return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
426    }
427
428    // A scalar source can be splatted to a vector of the same element type
429    if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
430      assert((cast<llvm::VectorType>(DstTy)->getElementType()
431              == Src->getType()) &&
432             "Vector element type must match scalar type to splat.");
433      unsigned NumElements = DstType->getAsVectorType()->getNumElements();
434      llvm::SmallVector<llvm::Constant*, 16> Elements;
435      for (unsigned i = 0; i < NumElements; i++)
436        Elements.push_back(Src);
437
438      return llvm::ConstantVector::get(&Elements[0], NumElements);
439    }
440
441    if (isa<llvm::VectorType>(Src->getType()) ||
442        isa<llvm::VectorType>(DstTy)) {
443      return llvm::ConstantExpr::getBitCast(Src, DstTy);
444    }
445
446    // Finally, we have the arithmetic types: real int/float.
447    if (isa<llvm::IntegerType>(Src->getType())) {
448      bool InputSigned = SrcType->isSignedIntegerType();
449      if (isa<llvm::IntegerType>(DstTy))
450        return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
451      else if (InputSigned)
452        return llvm::ConstantExpr::getSIToFP(Src, DstTy);
453      else
454        return llvm::ConstantExpr::getUIToFP(Src, DstTy);
455    }
456
457    assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
458    if (isa<llvm::IntegerType>(DstTy)) {
459      if (DstType->isSignedIntegerType())
460        return llvm::ConstantExpr::getFPToSI(Src, DstTy);
461      else
462        return llvm::ConstantExpr::getFPToUI(Src, DstTy);
463    }
464
465    assert(DstTy->isFloatingPoint() && "Unknown real conversion");
466    if (DstTy->getTypeID() < Src->getType()->getTypeID())
467      return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
468    else
469      return llvm::ConstantExpr::getFPExtend(Src, DstTy);
470  }
471
472public:
473  llvm::Constant *EmitLValue(Expr *E) {
474    switch (E->getStmtClass()) {
475    default: break;
476    case Expr::ParenExprClass:
477      // Elide parenthesis
478      return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
479    case Expr::CompoundLiteralExprClass: {
480      // Note that due to the nature of compound literals, this is guaranteed
481      // to be the only use of the variable, so we just generate it here.
482      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
483      llvm::Constant* C = Visit(CLE->getInitializer());
484      C = new llvm::GlobalVariable(C->getType(),E->getType().isConstQualified(),
485                                   llvm::GlobalValue::InternalLinkage,
486                                   C, ".compoundliteral", &CGM.getModule());
487      return C;
488    }
489    case Expr::DeclRefExprClass:
490    case Expr::QualifiedDeclRefExprClass: {
491      NamedDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
492      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
493        return CGM.GetAddrOfFunction(FD);
494      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
495        if (VD->isFileVarDecl())
496          return CGM.GetAddrOfGlobalVar(VD);
497        else if (VD->isBlockVarDecl()) {
498          assert(CGF && "Can't access static local vars without CGF");
499          return CGF->GetAddrOfStaticLocalVar(VD);
500        }
501      }
502      break;
503    }
504    case Expr::MemberExprClass: {
505      MemberExpr* ME = cast<MemberExpr>(E);
506      llvm::Constant *Base;
507      if (ME->isArrow())
508        Base = Visit(ME->getBase());
509      else
510        Base = EmitLValue(ME->getBase());
511
512      FieldDecl *Field = dyn_cast<FieldDecl>(ME->getMemberDecl());
513      // FIXME: Handle other kinds of member expressions.
514      assert(Field && "No code generation for non-field member expressions");
515      unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(Field);
516      llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
517      llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
518                                                   FieldNumber);
519      llvm::Value *Ops[] = {Zero, Idx};
520      return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
521    }
522    case Expr::ArraySubscriptExprClass: {
523      ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
524      llvm::Constant *Base = Visit(ASExpr->getBase());
525      llvm::Constant *Index = Visit(ASExpr->getIdx());
526      assert(!ASExpr->getBase()->getType()->isVectorType() &&
527             "Taking the address of a vector component is illegal!");
528      return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
529    }
530    case Expr::StringLiteralClass:
531      return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
532    case Expr::ObjCStringLiteralClass: {
533      ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
534      std::string S(SL->getString()->getStrData(),
535                    SL->getString()->getByteLength());
536      llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(S);
537      return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
538    }
539    case Expr::UnaryOperatorClass: {
540      UnaryOperator *Exp = cast<UnaryOperator>(E);
541      switch (Exp->getOpcode()) {
542      default: break;
543      case UnaryOperator::Extension:
544        // Extension is just a wrapper for expressions
545        return EmitLValue(Exp->getSubExpr());
546      case UnaryOperator::Real:
547      case UnaryOperator::Imag: {
548        // The address of __real or __imag is just a GEP off the address
549        // of the internal expression
550        llvm::Constant* C = EmitLValue(Exp->getSubExpr());
551        llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
552        llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
553                                       Exp->getOpcode() == UnaryOperator::Imag);
554        llvm::Value *Ops[] = {Zero, Idx};
555        return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
556      }
557      case UnaryOperator::Deref:
558        // The address of a deref is just the value of the expression
559        return Visit(Exp->getSubExpr());
560      }
561      break;
562    }
563
564    case Expr::PredefinedExprClass: {
565      // __func__/__FUNCTION__ -> "".  __PRETTY_FUNCTION__ -> "top level".
566      std::string Str;
567      if (cast<PredefinedExpr>(E)->getIdentType() ==
568          PredefinedExpr::PrettyFunction)
569        Str = "top level";
570
571      return CGM.GetAddrOfConstantCString(Str, ".tmp");
572    }
573    case Expr::AddrLabelExprClass: {
574      assert(CGF && "Invalid address of label expression outside function.");
575      unsigned id = CGF->GetIDForAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
576      llvm::Constant *C = llvm::ConstantInt::get(llvm::Type::Int32Ty, id);
577      return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
578    }
579    case Expr::CallExprClass: {
580      CallExpr* CE = cast<CallExpr>(E);
581      if (CE->isBuiltinCall() != Builtin::BI__builtin___CFStringMakeConstantString)
582        break;
583      const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
584      const StringLiteral *Literal = cast<StringLiteral>(Arg);
585      std::string S(Literal->getStrData(), Literal->getByteLength());
586      return CGM.GetAddrOfConstantCFString(S);
587    }
588    }
589    CGM.ErrorUnsupported(E, "constant l-value expression");
590    llvm::Type *Ty = llvm::PointerType::getUnqual(ConvertType(E->getType()));
591    return llvm::UndefValue::get(Ty);
592  }
593};
594
595}  // end anonymous namespace.
596
597llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
598                                                CodeGenFunction *CGF) {
599  QualType type = Context.getCanonicalType(E->getType());
600
601  Expr::EvalResult Result;
602
603  if (E->Evaluate(Result, Context)) {
604    assert(!Result.HasSideEffects &&
605           "Constant expr should not have any side effects!");
606    switch (Result.Val.getKind()) {
607    case APValue::Uninitialized:
608      assert(0 && "Constant expressions should be uninitialized.");
609      return llvm::UndefValue::get(getTypes().ConvertType(type));
610    case APValue::LValue: {
611      llvm::Constant *Offset =
612        llvm::ConstantInt::get(llvm::Type::Int64Ty,
613                               Result.Val.getLValueOffset());
614
615      if (const Expr *LVBase = Result.Val.getLValueBase()) {
616        llvm::Constant *C =
617          ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
618
619        const llvm::Type *Type =
620          llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
621        const llvm::Type *DestType = getTypes().ConvertTypeForMem(E->getType());
622
623        // FIXME: It's a little ugly that we need to cast to a pointer,
624        // apply the GEP and then cast back.
625        C = llvm::ConstantExpr::getBitCast(C, Type);
626        C = llvm::ConstantExpr::getGetElementPtr(C, &Offset, 1);
627
628        return llvm::ConstantExpr::getBitCast(C, DestType);
629      }
630
631      return llvm::ConstantExpr::getIntToPtr(Offset,
632                                             getTypes().ConvertType(type));
633    }
634    case APValue::Int: {
635      llvm::Constant *C = llvm::ConstantInt::get(Result.Val.getInt());
636
637      if (C->getType() == llvm::Type::Int1Ty) {
638        const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
639        C = llvm::ConstantExpr::getZExt(C, BoolTy);
640      }
641      return C;
642    }
643    case APValue::ComplexInt: {
644      llvm::Constant *Complex[2];
645
646      Complex[0] = llvm::ConstantInt::get(Result.Val.getComplexIntReal());
647      Complex[1] = llvm::ConstantInt::get(Result.Val.getComplexIntImag());
648
649      return llvm::ConstantStruct::get(Complex, 2);
650    }
651    case APValue::Float:
652      return llvm::ConstantFP::get(Result.Val.getFloat());
653    case APValue::ComplexFloat: {
654      llvm::Constant *Complex[2];
655
656      Complex[0] = llvm::ConstantFP::get(Result.Val.getComplexFloatReal());
657      Complex[1] = llvm::ConstantFP::get(Result.Val.getComplexFloatImag());
658
659      return llvm::ConstantStruct::get(Complex, 2);
660    }
661    case APValue::Vector: {
662      llvm::SmallVector<llvm::Constant *, 4> Inits;
663      unsigned NumElts = Result.Val.getVectorLength();
664
665      for (unsigned i = 0; i != NumElts; ++i) {
666        APValue &Elt = Result.Val.getVectorElt(i);
667        if (Elt.isInt())
668          Inits.push_back(llvm::ConstantInt::get(Elt.getInt()));
669        else
670          Inits.push_back(llvm::ConstantFP::get(Elt.getFloat()));
671      }
672      return llvm::ConstantVector::get(&Inits[0], Inits.size());
673    }
674    }
675  }
676
677  llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
678  if (C->getType() == llvm::Type::Int1Ty) {
679    const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
680    C = llvm::ConstantExpr::getZExt(C, BoolTy);
681  }
682  return C;
683}
684