CGExprConstant.cpp revision ef648c76745ee5e4105eec22dbc97fac18145bd6 
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 "clang/AST/AST.h"
17#include "llvm/Constants.h"
18#include "llvm/Function.h"
19#include "llvm/GlobalVariable.h"
20#include "llvm/Support/Compiler.h"
21using namespace clang;
22using namespace CodeGen;
23
24namespace  {
25class VISIBILITY_HIDDEN ConstExprEmitter :
26  public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
27  CodeGenModule &CGM;
28  CodeGenFunction *CGF;
29public:
30  ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
31    : CGM(cgm), CGF(cgf) {
32  }
33
34  //===--------------------------------------------------------------------===//
35  //                            Visitor Methods
36  //===--------------------------------------------------------------------===//
37
38  llvm::Constant *VisitStmt(Stmt *S) {
39    CGM.WarnUnsupported(S, "constant expression");
40    QualType T = cast<Expr>(S)->getType();
41    return llvm::UndefValue::get(CGM.getTypes().ConvertType(T));
42  }
43
44  llvm::Constant *VisitParenExpr(ParenExpr *PE) {
45    return Visit(PE->getSubExpr());
46  }
47
48  // Leaves
49  llvm::Constant *VisitIntegerLiteral(const IntegerLiteral *E) {
50    return llvm::ConstantInt::get(E->getValue());
51  }
52  llvm::Constant *VisitFloatingLiteral(const FloatingLiteral *E) {
53    return llvm::ConstantFP::get(E->getValue());
54  }
55  llvm::Constant *VisitCharacterLiteral(const CharacterLiteral *E) {
56    return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
57  }
58  llvm::Constant *VisitCXXBoolLiteralExpr(const CXXBoolLiteralExpr *E) {
59    return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
60  }
61
62  llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
63    return Visit(E->getInitializer());
64  }
65
66  llvm::Constant *VisitCastExpr(const CastExpr* E) {
67    llvm::Constant *C = Visit(E->getSubExpr());
68
69    return EmitConversion(C, E->getSubExpr()->getType(), E->getType());
70  }
71
72  llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
73    return Visit(DAE->getExpr());
74  }
75
76  llvm::Constant *EmitArrayInitialization(InitListExpr *ILE,
77                                          const llvm::ArrayType *AType) {
78    std::vector<llvm::Constant*> Elts;
79    unsigned NumInitElements = ILE->getNumInits();
80    // FIXME: Check for wide strings
81    if (NumInitElements > 0 && isa<StringLiteral>(ILE->getInit(0)) &&
82        ILE->getType()->getAsArrayType()->getElementType()->isCharType())
83      return Visit(ILE->getInit(0));
84    const llvm::Type *ElemTy = AType->getElementType();
85    unsigned NumElements = AType->getNumElements();
86
87    // Initialising an array requires us to automatically
88    // initialise any elements that have not been initialised explicitly
89    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
90
91    // Copy initializer elements.
92    unsigned i = 0;
93    for (; i < NumInitableElts; ++i) {
94
95      llvm::Constant *C = Visit(ILE->getInit(i));
96      assert (C && "Failed to create initializer expression");
97      Elts.push_back(C);
98    }
99
100    // Initialize remaining array elements.
101    for (; i < NumElements; ++i)
102      Elts.push_back(llvm::Constant::getNullValue(ElemTy));
103
104    return llvm::ConstantArray::get(AType, Elts);
105  }
106
107  llvm::Constant *EmitStructInitialization(InitListExpr *ILE,
108                                           const llvm::StructType *SType) {
109
110    TagDecl *TD = ILE->getType()->getAsRecordType()->getDecl();
111    std::vector<llvm::Constant*> Elts;
112    const CGRecordLayout *CGR = CGM.getTypes().getCGRecordLayout(TD);
113    unsigned NumInitElements = ILE->getNumInits();
114    unsigned NumElements = SType->getNumElements();
115
116    // Initialising an structure requires us to automatically
117    // initialise any elements that have not been initialised explicitly
118    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
119
120    // Copy initializer elements. Skip padding fields.
121    unsigned EltNo = 0;  // Element no in ILE
122    unsigned FieldNo = 0; // Field no in  SType
123    while (EltNo < NumInitableElts) {
124
125      // Zero initialize padding field.
126      if (CGR->isPaddingField(FieldNo)) {
127        const llvm::Type *FieldTy = SType->getElementType(FieldNo);
128        Elts.push_back(llvm::Constant::getNullValue(FieldTy));
129        FieldNo++;
130        continue;
131      }
132
133      llvm::Constant *C = Visit(ILE->getInit(EltNo));
134      assert (C && "Failed to create initializer expression");
135      Elts.push_back(C);
136      EltNo++;
137      FieldNo++;
138    }
139
140    // Initialize remaining structure elements.
141    for (unsigned i = Elts.size(); i < NumElements; ++i) {
142      const llvm::Type *FieldTy = SType->getElementType(i);
143      Elts.push_back(llvm::Constant::getNullValue(FieldTy));
144    }
145
146    return llvm::ConstantStruct::get(SType, Elts);
147  }
148
149  llvm::Constant *EmitVectorInitialization(InitListExpr *ILE,
150                                           const llvm::VectorType *VType) {
151
152    std::vector<llvm::Constant*> Elts;
153    unsigned NumInitElements = ILE->getNumInits();
154    unsigned NumElements = VType->getNumElements();
155
156    assert (NumInitElements == NumElements
157            && "Unsufficient vector init elelments");
158    // Copy initializer elements.
159    unsigned i = 0;
160    for (; i < NumElements; ++i) {
161
162      llvm::Constant *C = Visit(ILE->getInit(i));
163      assert (C && "Failed to create initializer expression");
164      Elts.push_back(C);
165    }
166
167    return llvm::ConstantVector::get(VType, Elts);
168  }
169
170  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
171    const llvm::CompositeType *CType =
172      dyn_cast<llvm::CompositeType>(ConvertType(ILE->getType()));
173
174    if (!CType) {
175        // We have a scalar in braces. Just use the first element.
176        return Visit(ILE->getInit(0));
177    }
178
179    if (const llvm::ArrayType *AType = dyn_cast<llvm::ArrayType>(CType))
180      return EmitArrayInitialization(ILE, AType);
181
182    if (const llvm::StructType *SType = dyn_cast<llvm::StructType>(CType))
183      return EmitStructInitialization(ILE, SType);
184
185    if (const llvm::VectorType *VType = dyn_cast<llvm::VectorType>(CType))
186      return EmitVectorInitialization(ILE, VType);
187
188    // Make sure we have an array at this point
189    assert(0 && "Unable to handle InitListExpr");
190    // Get rid of control reaches end of void function warning.
191    // Not reached.
192    return 0;
193  }
194
195  llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
196    Expr* SExpr = ICExpr->getSubExpr();
197    QualType SType = SExpr->getType();
198    llvm::Constant *C; // the intermediate expression
199    QualType T;        // the type of the intermediate expression
200    if (SType->isArrayType()) {
201      // Arrays decay to a pointer to the first element
202      // VLAs would require special handling, but they can't occur here
203      C = EmitLValue(SExpr);
204      llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
205      llvm::Constant *Ops[] = {Idx0, Idx0};
206      C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
207
208      QualType ElemType = SType->getAsArrayType()->getElementType();
209      T = CGM.getContext().getPointerType(ElemType);
210    } else if (SType->isFunctionType()) {
211      // Function types decay to a pointer to the function
212      C = EmitLValue(SExpr);
213      T = CGM.getContext().getPointerType(SType);
214    } else {
215      C = Visit(SExpr);
216      T = SType;
217    }
218
219    // Perform the conversion; note that an implicit cast can both promote
220    // and convert an array/function
221    return EmitConversion(C, T, ICExpr->getType());
222  }
223
224  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
225    const char *StrData = E->getStrData();
226    unsigned Len = E->getByteLength();
227    assert(!E->getType()->isPointerType() && "Strings are always arrays");
228
229    // Otherwise this must be a string initializing an array in a static
230    // initializer.  Don't emit it as the address of the string, emit the string
231    // data itself as an inline array.
232    const ConstantArrayType *CAT = E->getType()->getAsConstantArrayType();
233    assert(CAT && "String isn't pointer or array!");
234
235    std::string Str(StrData, StrData + Len);
236    // Null terminate the string before potentially truncating it.
237    // FIXME: What about wchar_t strings?
238    Str.push_back(0);
239
240    uint64_t RealLen = CAT->getSize().getZExtValue();
241    // String or grow the initializer to the required size.
242    if (RealLen != Str.size())
243      Str.resize(RealLen);
244
245    return llvm::ConstantArray::get(Str, false);
246  }
247
248  llvm::Constant *VisitDeclRefExpr(DeclRefExpr *E) {
249    const ValueDecl *Decl = E->getDecl();
250    if (const EnumConstantDecl *EC = dyn_cast<EnumConstantDecl>(Decl))
251      return llvm::ConstantInt::get(EC->getInitVal());
252    assert(0 && "Unsupported decl ref type!");
253    return 0;
254  }
255
256  llvm::Constant *VisitSizeOfAlignOfTypeExpr(const SizeOfAlignOfTypeExpr *E) {
257    return EmitSizeAlignOf(E->getArgumentType(), E->getType(), E->isSizeOf());
258  }
259
260  // Unary operators
261  llvm::Constant *VisitUnaryPlus(const UnaryOperator *E) {
262    return Visit(E->getSubExpr());
263  }
264  llvm::Constant *VisitUnaryMinus(const UnaryOperator *E) {
265    return llvm::ConstantExpr::getNeg(Visit(E->getSubExpr()));
266  }
267  llvm::Constant *VisitUnaryNot(const UnaryOperator *E) {
268    return llvm::ConstantExpr::getNot(Visit(E->getSubExpr()));
269  }
270  llvm::Constant *VisitUnaryLNot(const UnaryOperator *E) {
271    llvm::Constant *SubExpr = Visit(E->getSubExpr());
272
273    if (E->getSubExpr()->getType()->isRealFloatingType()) {
274      // Compare against 0.0 for fp scalars.
275      llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
276      SubExpr = llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UEQ, SubExpr,
277                                            Zero);
278    } else {
279      assert((E->getSubExpr()->getType()->isIntegerType() ||
280              E->getSubExpr()->getType()->isPointerType()) &&
281             "Unknown scalar type to convert");
282      // Compare against an integer or pointer null.
283      llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
284      SubExpr = llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_EQ, SubExpr,
285                                            Zero);
286    }
287
288    return llvm::ConstantExpr::getZExt(SubExpr, ConvertType(E->getType()));
289  }
290  llvm::Constant *VisitUnarySizeOf(const UnaryOperator *E) {
291    return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), true);
292  }
293  llvm::Constant *VisitUnaryAlignOf(const UnaryOperator *E) {
294    return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), false);
295  }
296  llvm::Constant *VisitUnaryAddrOf(const UnaryOperator *E) {
297    return EmitLValue(E->getSubExpr());
298  }
299  llvm::Constant *VisitUnaryOffsetOf(const UnaryOperator *E) {
300    int64_t Val = E->evaluateOffsetOf(CGM.getContext());
301
302    assert(E->getType()->isIntegerType() && "Result type must be an integer!");
303
304    uint32_t ResultWidth =
305      static_cast<uint32_t>(CGM.getContext().getTypeSize(E->getType()));
306    return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
307  }
308
309  // Binary operators
310  llvm::Constant *VisitBinOr(const BinaryOperator *E) {
311    llvm::Constant *LHS = Visit(E->getLHS());
312    llvm::Constant *RHS = Visit(E->getRHS());
313
314    return llvm::ConstantExpr::getOr(LHS, RHS);
315  }
316  llvm::Constant *VisitBinSub(const BinaryOperator *E) {
317    llvm::Constant *LHS = Visit(E->getLHS());
318    llvm::Constant *RHS = Visit(E->getRHS());
319
320    if (!isa<llvm::PointerType>(RHS->getType())) {
321      // pointer - int
322      if (isa<llvm::PointerType>(LHS->getType())) {
323        llvm::Constant *Idx = llvm::ConstantExpr::getNeg(RHS);
324
325        return llvm::ConstantExpr::getGetElementPtr(LHS, &Idx, 1);
326      }
327
328      // int - int
329      return llvm::ConstantExpr::getSub(LHS, RHS);
330    }
331
332    assert(0 && "Unhandled bin sub case!");
333    return 0;
334  }
335
336  llvm::Constant *VisitBinShl(const BinaryOperator *E) {
337    llvm::Constant *LHS = Visit(E->getLHS());
338    llvm::Constant *RHS = Visit(E->getRHS());
339
340    // LLVM requires the LHS and RHS to be the same type: promote or truncate the
341    // RHS to the same size as the LHS.
342    if (LHS->getType() != RHS->getType())
343      RHS = llvm::ConstantExpr::getIntegerCast(RHS, LHS->getType(), false);
344
345    return llvm::ConstantExpr::getShl(LHS, RHS);
346  }
347
348  llvm::Constant *VisitBinMul(const BinaryOperator *E) {
349    llvm::Constant *LHS = Visit(E->getLHS());
350    llvm::Constant *RHS = Visit(E->getRHS());
351
352    return llvm::ConstantExpr::getMul(LHS, RHS);
353  }
354
355  llvm::Constant *VisitBinDiv(const BinaryOperator *E) {
356    llvm::Constant *LHS = Visit(E->getLHS());
357    llvm::Constant *RHS = Visit(E->getRHS());
358
359    if (LHS->getType()->isFPOrFPVector())
360      return llvm::ConstantExpr::getFDiv(LHS, RHS);
361    else if (E->getType()->isUnsignedIntegerType())
362      return llvm::ConstantExpr::getUDiv(LHS, RHS);
363    else
364      return llvm::ConstantExpr::getSDiv(LHS, RHS);
365  }
366
367  llvm::Constant *VisitBinAdd(const BinaryOperator *E) {
368    llvm::Constant *LHS = Visit(E->getLHS());
369    llvm::Constant *RHS = Visit(E->getRHS());
370
371    if (!E->getType()->isPointerType())
372      return llvm::ConstantExpr::getAdd(LHS, RHS);
373
374    llvm::Constant *Ptr, *Idx;
375    if (isa<llvm::PointerType>(LHS->getType())) { // pointer + int
376      Ptr = LHS;
377      Idx = RHS;
378    } else { // int + pointer
379      Ptr = RHS;
380      Idx = LHS;
381    }
382
383    return llvm::ConstantExpr::getGetElementPtr(Ptr, &Idx, 1);
384  }
385
386  llvm::Constant *VisitBinAnd(const BinaryOperator *E) {
387    llvm::Constant *LHS = Visit(E->getLHS());
388    llvm::Constant *RHS = Visit(E->getRHS());
389
390    return llvm::ConstantExpr::getAnd(LHS, RHS);
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    SrcType = SrcType.getCanonicalType();
418    DstType = DstType.getCanonicalType();
419    if (SrcType == DstType) return Src;
420
421    // Handle conversions to bool first, they are special: comparisons against 0.
422    if (DstType->isBooleanType())
423      return EmitConversionToBool(Src, SrcType);
424
425    const llvm::Type *DstTy = ConvertType(DstType);
426
427    // Ignore conversions like int -> uint.
428    if (Src->getType() == DstTy)
429      return Src;
430
431    // Handle pointer conversions next: pointers can only be converted to/from
432    // other pointers and integers.
433    if (isa<PointerType>(DstType)) {
434      // The source value may be an integer, or a pointer.
435      if (isa<llvm::PointerType>(Src->getType()))
436        return llvm::ConstantExpr::getBitCast(Src, DstTy);
437      assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
438      return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
439    }
440
441    if (isa<PointerType>(SrcType)) {
442      // Must be an ptr to int cast.
443      assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
444      return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
445    }
446
447    // A scalar source can be splatted to a vector of the same element type
448    if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
449      const llvm::VectorType *VT = cast<llvm::VectorType>(DstTy);
450      assert((VT->getElementType() == Src->getType()) &&
451             "Vector element type must match scalar type to splat.");
452      unsigned NumElements = DstType->getAsVectorType()->getNumElements();
453      llvm::SmallVector<llvm::Constant*, 16> Elements;
454      for (unsigned i = 0; i < NumElements; i++)
455        Elements.push_back(Src);
456
457      return llvm::ConstantVector::get(&Elements[0], NumElements);
458    }
459
460    if (isa<llvm::VectorType>(Src->getType()) ||
461        isa<llvm::VectorType>(DstTy)) {
462      return llvm::ConstantExpr::getBitCast(Src, DstTy);
463    }
464
465    // Finally, we have the arithmetic types: real int/float.
466    if (isa<llvm::IntegerType>(Src->getType())) {
467      bool InputSigned = SrcType->isSignedIntegerType();
468      if (isa<llvm::IntegerType>(DstTy))
469        return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
470      else if (InputSigned)
471        return llvm::ConstantExpr::getSIToFP(Src, DstTy);
472      else
473        return llvm::ConstantExpr::getUIToFP(Src, DstTy);
474    }
475
476    assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
477    if (isa<llvm::IntegerType>(DstTy)) {
478      if (DstType->isSignedIntegerType())
479        return llvm::ConstantExpr::getFPToSI(Src, DstTy);
480      else
481        return llvm::ConstantExpr::getFPToUI(Src, DstTy);
482    }
483
484    assert(DstTy->isFloatingPoint() && "Unknown real conversion");
485    if (DstTy->getTypeID() < Src->getType()->getTypeID())
486      return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
487    else
488      return llvm::ConstantExpr::getFPExtend(Src, DstTy);
489  }
490
491  llvm::Constant *EmitSizeAlignOf(QualType TypeToSize,
492                                  QualType RetType, bool isSizeOf) {
493    std::pair<uint64_t, unsigned> Info =
494      CGM.getContext().getTypeInfo(TypeToSize);
495
496    uint64_t Val = isSizeOf ? Info.first : Info.second;
497    Val /= 8;  // Return size in bytes, not bits.
498
499    assert(RetType->isIntegerType() && "Result type must be an integer!");
500
501    uint32_t ResultWidth =
502      static_cast<uint32_t>(CGM.getContext().getTypeSize(RetType));
503    return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
504  }
505
506  llvm::Constant *EmitLValue(Expr *E) {
507    switch (E->getStmtClass()) {
508    default: break;
509    case Expr::ParenExprClass:
510      // Elide parenthesis
511      return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
512    case Expr::CompoundLiteralExprClass: {
513      // Note that due to the nature of compound literals, this is guaranteed
514      // to be the only use of the variable, so we just generate it here.
515      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
516      llvm::Constant* C = Visit(CLE->getInitializer());
517      C = new llvm::GlobalVariable(C->getType(),E->getType().isConstQualified(),
518                                   llvm::GlobalValue::InternalLinkage,
519                                   C, ".compoundliteral", &CGM.getModule());
520      return C;
521    }
522    case Expr::DeclRefExprClass: {
523      ValueDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
524      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
525        return CGM.GetAddrOfFunctionDecl(FD, false);
526      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
527        if (VD->isFileVarDecl())
528          return CGM.GetAddrOfGlobalVar(VD, false);
529        else if (VD->isBlockVarDecl()) {
530          assert(CGF && "Can't access static local vars without CGF");
531          return CGF->GetAddrOfStaticLocalVar(VD);
532        }
533      }
534      break;
535    }
536    case Expr::MemberExprClass: {
537      MemberExpr* ME = cast<MemberExpr>(E);
538      llvm::Constant *Base;
539      if (ME->isArrow())
540        Base = Visit(ME->getBase());
541      else
542        Base = EmitLValue(ME->getBase());
543
544      unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(ME->getMemberDecl());
545      llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
546      llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
547                                                   FieldNumber);
548      llvm::Value *Ops[] = {Zero, Idx};
549      return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
550    }
551    case Expr::ArraySubscriptExprClass: {
552      ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
553      llvm::Constant *Base = Visit(ASExpr->getBase());
554      llvm::Constant *Index = Visit(ASExpr->getIdx());
555      assert(!ASExpr->getBase()->getType()->isVectorType() &&
556             "Taking the address of a vector component is illegal!");
557      return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
558    }
559    case Expr::StringLiteralClass: {
560      StringLiteral *String = cast<StringLiteral>(E);
561      assert(!String->isWide() && "Cannot codegen wide strings yet");
562      const char *StrData = String->getStrData();
563      unsigned Len = String->getByteLength();
564
565      return CGM.GetAddrOfConstantString(std::string(StrData, StrData + Len));
566    }
567    case Expr::UnaryOperatorClass: {
568      UnaryOperator *Exp = cast<UnaryOperator>(E);
569      switch (Exp->getOpcode()) {
570      default: break;
571      case UnaryOperator::Extension:
572        // Extension is just a wrapper for expressions
573        return EmitLValue(Exp->getSubExpr());
574      case UnaryOperator::Real:
575      case UnaryOperator::Imag: {
576        // The address of __real or __imag is just a GEP off the address
577        // of the internal expression
578        llvm::Constant* C = EmitLValue(Exp->getSubExpr());
579        llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
580        llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
581                                       Exp->getOpcode() == UnaryOperator::Imag);
582        llvm::Value *Ops[] = {Zero, Idx};
583        return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
584      }
585      case UnaryOperator::Deref:
586        // The address of a deref is just the value of the expression
587        return Visit(Exp->getSubExpr());
588      }
589      break;
590    }
591    }
592    CGM.WarnUnsupported(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
599}  // end anonymous namespace.
600
601
602llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
603                                                CodeGenFunction *CGF)
604{
605  QualType type = E->getType().getCanonicalType();
606
607  if (type->isIntegerType()) {
608    llvm::APSInt Value(static_cast<uint32_t>(Context.getTypeSize(type)));
609    if (E->isIntegerConstantExpr(Value, Context)) {
610      return llvm::ConstantInt::get(Value);
611    }
612  }
613
614  return ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
615}
616