CGExprConstant.cpp revision 248a753f6b670692523c99afaeb8fe98f7ae3ca7 
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(ConvertType(E->getType()), 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      // FIXME: Remove this when sema of initializers is finished (and the code
97      // above).
98      if (C == 0 && ILE->getInit(i)->getType()->isVoidType()) {
99        if (ILE->getType()->isVoidType()) return 0;
100        return llvm::UndefValue::get(AType);
101      }
102      assert (C && "Failed to create initializer expression");
103      Elts.push_back(C);
104    }
105
106    // Initialize remaining array elements.
107    for (; i < NumElements; ++i)
108      Elts.push_back(llvm::Constant::getNullValue(ElemTy));
109
110    return llvm::ConstantArray::get(AType, Elts);
111  }
112
113  llvm::Constant *EmitStructInitialization(InitListExpr *ILE,
114                                           const llvm::StructType *SType) {
115
116    TagDecl *TD = ILE->getType()->getAsRecordType()->getDecl();
117    std::vector<llvm::Constant*> Elts;
118    const CGRecordLayout *CGR = CGM.getTypes().getCGRecordLayout(TD);
119    unsigned NumInitElements = ILE->getNumInits();
120    unsigned NumElements = SType->getNumElements();
121
122    // Initialising an structure requires us to automatically
123    // initialise any elements that have not been initialised explicitly
124    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
125
126    // Copy initializer elements. Skip padding fields.
127    unsigned EltNo = 0;  // Element no in ILE
128    unsigned FieldNo = 0; // Field no in  SType
129    while (EltNo < NumInitableElts) {
130
131      // Zero initialize padding field.
132      if (CGR->isPaddingField(FieldNo)) {
133        const llvm::Type *FieldTy = SType->getElementType(FieldNo);
134        Elts.push_back(llvm::Constant::getNullValue(FieldTy));
135        FieldNo++;
136        continue;
137      }
138
139      llvm::Constant *C = Visit(ILE->getInit(EltNo));
140      // FIXME: Remove this when sema of initializers is finished (and the code
141      // above).
142      if (C == 0 && ILE->getInit(EltNo)->getType()->isVoidType()) {
143        if (ILE->getType()->isVoidType()) return 0;
144        return llvm::UndefValue::get(SType);
145      }
146      assert (C && "Failed to create initializer expression");
147      Elts.push_back(C);
148      EltNo++;
149      FieldNo++;
150    }
151
152    // Initialize remaining structure elements.
153    for (unsigned i = Elts.size(); i < NumElements; ++i) {
154      const llvm::Type *FieldTy = SType->getElementType(i);
155      Elts.push_back(llvm::Constant::getNullValue(FieldTy));
156    }
157
158    return llvm::ConstantStruct::get(SType, Elts);
159  }
160
161  llvm::Constant *EmitVectorInitialization(InitListExpr *ILE,
162                                           const llvm::VectorType *VType) {
163
164    std::vector<llvm::Constant*> Elts;
165    unsigned NumInitElements = ILE->getNumInits();
166    unsigned NumElements = VType->getNumElements();
167
168    assert (NumInitElements == NumElements
169            && "Unsufficient vector init elelments");
170    // Copy initializer elements.
171    unsigned i = 0;
172    for (; i < NumElements; ++i) {
173
174      llvm::Constant *C = Visit(ILE->getInit(i));
175      // FIXME: Remove this when sema of initializers is finished (and the code
176      // above).
177      if (C == 0 && ILE->getInit(i)->getType()->isVoidType()) {
178        if (ILE->getType()->isVoidType()) return 0;
179        return llvm::UndefValue::get(VType);
180      }
181      assert (C && "Failed to create initializer expression");
182      Elts.push_back(C);
183    }
184
185    return llvm::ConstantVector::get(VType, Elts);
186  }
187
188  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
189    const llvm::CompositeType *CType =
190      dyn_cast<llvm::CompositeType>(ConvertType(ILE->getType()));
191
192    if (!CType) {
193        // We have a scalar in braces. Just use the first element.
194        return Visit(ILE->getInit(0));
195    }
196
197    if (const llvm::ArrayType *AType = dyn_cast<llvm::ArrayType>(CType))
198      return EmitArrayInitialization(ILE, AType);
199
200    if (const llvm::StructType *SType = dyn_cast<llvm::StructType>(CType))
201      return EmitStructInitialization(ILE, SType);
202
203    if (const llvm::VectorType *VType = dyn_cast<llvm::VectorType>(CType))
204      return EmitVectorInitialization(ILE, VType);
205
206    // Make sure we have an array at this point
207    assert(0 && "Unable to handle InitListExpr");
208    // Get rid of control reaches end of void function warning.
209    // Not reached.
210    return 0;
211  }
212
213  llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
214    Expr* SExpr = ICExpr->getSubExpr();
215    QualType SType = SExpr->getType();
216    llvm::Constant *C; // the intermediate expression
217    QualType T;        // the type of the intermediate expression
218    if (SType->isArrayType()) {
219      // Arrays decay to a pointer to the first element
220      // VLAs would require special handling, but they can't occur here
221      C = EmitLValue(SExpr);
222      llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
223      llvm::Constant *Ops[] = {Idx0, Idx0};
224      C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
225
226      QualType ElemType = SType->getAsArrayType()->getElementType();
227      T = CGM.getContext().getPointerType(ElemType);
228    } else if (SType->isFunctionType()) {
229      // Function types decay to a pointer to the function
230      C = EmitLValue(SExpr);
231      T = CGM.getContext().getPointerType(SType);
232    } else {
233      C = Visit(SExpr);
234      T = SType;
235    }
236
237    // Perform the conversion; note that an implicit cast can both promote
238    // and convert an array/function
239    return EmitConversion(C, T, ICExpr->getType());
240  }
241
242  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
243    const char *StrData = E->getStrData();
244    unsigned Len = E->getByteLength();
245    assert(!E->getType()->isPointerType() && "Strings are always arrays");
246
247    // Otherwise this must be a string initializing an array in a static
248    // initializer.  Don't emit it as the address of the string, emit the string
249    // data itself as an inline array.
250    const ConstantArrayType *CAT = E->getType()->getAsConstantArrayType();
251    assert(CAT && "String isn't pointer or array!");
252
253    std::string Str(StrData, StrData + Len);
254    // Null terminate the string before potentially truncating it.
255    // FIXME: What about wchar_t strings?
256    Str.push_back(0);
257
258    uint64_t RealLen = CAT->getSize().getZExtValue();
259    // String or grow the initializer to the required size.
260    if (RealLen != Str.size())
261      Str.resize(RealLen);
262
263    return llvm::ConstantArray::get(Str, false);
264  }
265
266  llvm::Constant *VisitDeclRefExpr(DeclRefExpr *E) {
267    const ValueDecl *Decl = E->getDecl();
268    if (const EnumConstantDecl *EC = dyn_cast<EnumConstantDecl>(Decl))
269      return llvm::ConstantInt::get(EC->getInitVal());
270    assert(0 && "Unsupported decl ref type!");
271    return 0;
272  }
273
274  llvm::Constant *VisitSizeOfAlignOfTypeExpr(const SizeOfAlignOfTypeExpr *E) {
275    return EmitSizeAlignOf(E->getArgumentType(), E->getType(), E->isSizeOf());
276  }
277
278  // Unary operators
279  llvm::Constant *VisitUnaryPlus(const UnaryOperator *E) {
280    return Visit(E->getSubExpr());
281  }
282  llvm::Constant *VisitUnaryMinus(const UnaryOperator *E) {
283    return llvm::ConstantExpr::getNeg(Visit(E->getSubExpr()));
284  }
285  llvm::Constant *VisitUnaryNot(const UnaryOperator *E) {
286    return llvm::ConstantExpr::getNot(Visit(E->getSubExpr()));
287  }
288  llvm::Constant *VisitUnaryLNot(const UnaryOperator *E) {
289    llvm::Constant *SubExpr = Visit(E->getSubExpr());
290
291    if (E->getSubExpr()->getType()->isRealFloatingType()) {
292      // Compare against 0.0 for fp scalars.
293      llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
294      SubExpr = llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UEQ, SubExpr,
295                                            Zero);
296    } else {
297      assert((E->getSubExpr()->getType()->isIntegerType() ||
298              E->getSubExpr()->getType()->isPointerType()) &&
299             "Unknown scalar type to convert");
300      // Compare against an integer or pointer null.
301      llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
302      SubExpr = llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_EQ, SubExpr,
303                                            Zero);
304    }
305
306    return llvm::ConstantExpr::getZExt(SubExpr, ConvertType(E->getType()));
307  }
308  llvm::Constant *VisitUnarySizeOf(const UnaryOperator *E) {
309    return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), true);
310  }
311  llvm::Constant *VisitUnaryAlignOf(const UnaryOperator *E) {
312    return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), false);
313  }
314  llvm::Constant *VisitUnaryAddrOf(const UnaryOperator *E) {
315    return EmitLValue(E->getSubExpr());
316  }
317  llvm::Constant *VisitUnaryOffsetOf(const UnaryOperator *E) {
318    int64_t Val = E->evaluateOffsetOf(CGM.getContext());
319
320    assert(E->getType()->isIntegerType() && "Result type must be an integer!");
321
322    uint32_t ResultWidth =
323      static_cast<uint32_t>(CGM.getContext().getTypeSize(E->getType()));
324    return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
325  }
326
327  // Binary operators
328  llvm::Constant *VisitBinOr(const BinaryOperator *E) {
329    llvm::Constant *LHS = Visit(E->getLHS());
330    llvm::Constant *RHS = Visit(E->getRHS());
331
332    return llvm::ConstantExpr::getOr(LHS, RHS);
333  }
334  llvm::Constant *VisitBinSub(const BinaryOperator *E) {
335    llvm::Constant *LHS = Visit(E->getLHS());
336    llvm::Constant *RHS = Visit(E->getRHS());
337
338    if (!isa<llvm::PointerType>(RHS->getType())) {
339      // pointer - int
340      if (isa<llvm::PointerType>(LHS->getType())) {
341        llvm::Constant *Idx = llvm::ConstantExpr::getNeg(RHS);
342
343        return llvm::ConstantExpr::getGetElementPtr(LHS, &Idx, 1);
344      }
345
346      // int - int
347      return llvm::ConstantExpr::getSub(LHS, RHS);
348    }
349
350    assert(0 && "Unhandled bin sub case!");
351    return 0;
352  }
353
354  llvm::Constant *VisitBinShl(const BinaryOperator *E) {
355    llvm::Constant *LHS = Visit(E->getLHS());
356    llvm::Constant *RHS = Visit(E->getRHS());
357
358    // LLVM requires the LHS and RHS to be the same type: promote or truncate the
359    // RHS to the same size as the LHS.
360    if (LHS->getType() != RHS->getType())
361      RHS = llvm::ConstantExpr::getIntegerCast(RHS, LHS->getType(), false);
362
363    return llvm::ConstantExpr::getShl(LHS, RHS);
364  }
365
366  llvm::Constant *VisitBinMul(const BinaryOperator *E) {
367    llvm::Constant *LHS = Visit(E->getLHS());
368    llvm::Constant *RHS = Visit(E->getRHS());
369
370    return llvm::ConstantExpr::getMul(LHS, RHS);
371  }
372
373  llvm::Constant *VisitBinDiv(const BinaryOperator *E) {
374    llvm::Constant *LHS = Visit(E->getLHS());
375    llvm::Constant *RHS = Visit(E->getRHS());
376
377    if (LHS->getType()->isFPOrFPVector())
378      return llvm::ConstantExpr::getFDiv(LHS, RHS);
379    else if (E->getType()->isUnsignedIntegerType())
380      return llvm::ConstantExpr::getUDiv(LHS, RHS);
381    else
382      return llvm::ConstantExpr::getSDiv(LHS, RHS);
383  }
384
385  llvm::Constant *VisitBinAdd(const BinaryOperator *E) {
386    llvm::Constant *LHS = Visit(E->getLHS());
387    llvm::Constant *RHS = Visit(E->getRHS());
388
389    if (!E->getType()->isPointerType())
390      return llvm::ConstantExpr::getAdd(LHS, RHS);
391
392    llvm::Constant *Ptr, *Idx;
393    if (isa<llvm::PointerType>(LHS->getType())) { // pointer + int
394      Ptr = LHS;
395      Idx = RHS;
396    } else { // int + pointer
397      Ptr = RHS;
398      Idx = LHS;
399    }
400
401    return llvm::ConstantExpr::getGetElementPtr(Ptr, &Idx, 1);
402  }
403
404  llvm::Constant *VisitBinAnd(const BinaryOperator *E) {
405    llvm::Constant *LHS = Visit(E->getLHS());
406    llvm::Constant *RHS = Visit(E->getRHS());
407
408    return llvm::ConstantExpr::getAnd(LHS, RHS);
409  }
410
411  // Utility methods
412  const llvm::Type *ConvertType(QualType T) {
413    return CGM.getTypes().ConvertType(T);
414  }
415
416  llvm::Constant *EmitConversionToBool(llvm::Constant *Src, QualType SrcType) {
417    assert(SrcType->isCanonical() && "EmitConversion strips typedefs");
418
419    if (SrcType->isRealFloatingType()) {
420      // Compare against 0.0 for fp scalars.
421      llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
422      return llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UNE, Src, Zero);
423    }
424
425    assert((SrcType->isIntegerType() || SrcType->isPointerType()) &&
426           "Unknown scalar type to convert");
427
428    // Compare against an integer or pointer null.
429    llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
430    return llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_NE, Src, Zero);
431  }
432
433  llvm::Constant *EmitConversion(llvm::Constant *Src, QualType SrcType,
434                                 QualType DstType) {
435    SrcType = SrcType.getCanonicalType();
436    DstType = DstType.getCanonicalType();
437    if (SrcType == DstType) return Src;
438
439    // Handle conversions to bool first, they are special: comparisons against 0.
440    if (DstType->isBooleanType())
441      return EmitConversionToBool(Src, SrcType);
442
443    const llvm::Type *DstTy = ConvertType(DstType);
444
445    // Ignore conversions like int -> uint.
446    if (Src->getType() == DstTy)
447      return Src;
448
449    // Handle pointer conversions next: pointers can only be converted to/from
450    // other pointers and integers.
451    if (isa<PointerType>(DstType)) {
452      // The source value may be an integer, or a pointer.
453      if (isa<llvm::PointerType>(Src->getType()))
454        return llvm::ConstantExpr::getBitCast(Src, DstTy);
455      assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
456      return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
457    }
458
459    if (isa<PointerType>(SrcType)) {
460      // Must be an ptr to int cast.
461      assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
462      return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
463    }
464
465    // A scalar source can be splatted to a vector of the same element type
466    if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
467      const llvm::VectorType *VT = cast<llvm::VectorType>(DstTy);
468      assert((VT->getElementType() == Src->getType()) &&
469             "Vector element type must match scalar type to splat.");
470      unsigned NumElements = DstType->getAsVectorType()->getNumElements();
471      llvm::SmallVector<llvm::Constant*, 16> Elements;
472      for (unsigned i = 0; i < NumElements; i++)
473        Elements.push_back(Src);
474
475      return llvm::ConstantVector::get(&Elements[0], NumElements);
476    }
477
478    if (isa<llvm::VectorType>(Src->getType()) ||
479        isa<llvm::VectorType>(DstTy)) {
480      return llvm::ConstantExpr::getBitCast(Src, DstTy);
481    }
482
483    // Finally, we have the arithmetic types: real int/float.
484    if (isa<llvm::IntegerType>(Src->getType())) {
485      bool InputSigned = SrcType->isSignedIntegerType();
486      if (isa<llvm::IntegerType>(DstTy))
487        return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
488      else if (InputSigned)
489        return llvm::ConstantExpr::getSIToFP(Src, DstTy);
490      else
491        return llvm::ConstantExpr::getUIToFP(Src, DstTy);
492    }
493
494    assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
495    if (isa<llvm::IntegerType>(DstTy)) {
496      if (DstType->isSignedIntegerType())
497        return llvm::ConstantExpr::getFPToSI(Src, DstTy);
498      else
499        return llvm::ConstantExpr::getFPToUI(Src, DstTy);
500    }
501
502    assert(DstTy->isFloatingPoint() && "Unknown real conversion");
503    if (DstTy->getTypeID() < Src->getType()->getTypeID())
504      return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
505    else
506      return llvm::ConstantExpr::getFPExtend(Src, DstTy);
507  }
508
509  llvm::Constant *EmitSizeAlignOf(QualType TypeToSize,
510                                  QualType RetType, bool isSizeOf) {
511    std::pair<uint64_t, unsigned> Info =
512      CGM.getContext().getTypeInfo(TypeToSize);
513
514    uint64_t Val = isSizeOf ? Info.first : Info.second;
515    Val /= 8;  // Return size in bytes, not bits.
516
517    assert(RetType->isIntegerType() && "Result type must be an integer!");
518
519    uint32_t ResultWidth =
520      static_cast<uint32_t>(CGM.getContext().getTypeSize(RetType));
521    return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
522  }
523
524  llvm::Constant *EmitLValue(Expr *E) {
525    switch (E->getStmtClass()) {
526    default: break;
527    case Expr::ParenExprClass:
528      // Elide parenthesis
529      return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
530    case Expr::CompoundLiteralExprClass: {
531      // Note that due to the nature of compound literals, this is guaranteed
532      // to be the only use of the variable, so we just generate it here.
533      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
534      llvm::Constant* C = Visit(CLE->getInitializer());
535      C = new llvm::GlobalVariable(C->getType(),E->getType().isConstQualified(),
536                                   llvm::GlobalValue::InternalLinkage,
537                                   C, ".compoundliteral", &CGM.getModule());
538      return C;
539    }
540    case Expr::DeclRefExprClass: {
541      ValueDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
542      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
543        return CGM.GetAddrOfFunctionDecl(FD, false);
544      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
545        if (VD->isFileVarDecl())
546          return CGM.GetAddrOfGlobalVar(VD, false);
547        else if (VD->isBlockVarDecl()) {
548          assert(CGF && "Can't access static local vars without CGF");
549          return CGF->GetAddrOfStaticLocalVar(VD);
550        }
551      }
552      break;
553    }
554    case Expr::MemberExprClass: {
555      MemberExpr* ME = cast<MemberExpr>(E);
556      llvm::Constant *Base;
557      if (ME->isArrow())
558        Base = Visit(ME->getBase());
559      else
560        Base = EmitLValue(ME->getBase());
561
562      unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(ME->getMemberDecl());
563      llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
564      llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
565                                                   FieldNumber);
566      llvm::Value *Ops[] = {Zero, Idx};
567      return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
568    }
569    case Expr::ArraySubscriptExprClass: {
570      ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
571      llvm::Constant *Base = Visit(ASExpr->getBase());
572      llvm::Constant *Index = Visit(ASExpr->getIdx());
573      assert(!ASExpr->getBase()->getType()->isVectorType() &&
574             "Taking the address of a vector component is illegal!");
575      return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
576    }
577    case Expr::StringLiteralClass: {
578      StringLiteral *String = cast<StringLiteral>(E);
579      assert(!String->isWide() && "Cannot codegen wide strings yet");
580      const char *StrData = String->getStrData();
581      unsigned Len = String->getByteLength();
582
583      return CGM.GetAddrOfConstantString(std::string(StrData, StrData + Len));
584    }
585    case Expr::UnaryOperatorClass: {
586      UnaryOperator *Exp = cast<UnaryOperator>(E);
587      switch (Exp->getOpcode()) {
588      default: break;
589      case UnaryOperator::Extension:
590        // Extension is just a wrapper for expressions
591        return EmitLValue(Exp->getSubExpr());
592      case UnaryOperator::Real:
593      case UnaryOperator::Imag: {
594        // The address of __real or __imag is just a GEP off the address
595        // of the internal expression
596        llvm::Constant* C = EmitLValue(Exp->getSubExpr());
597        llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
598        llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
599                                       Exp->getOpcode() == UnaryOperator::Imag);
600        llvm::Value *Ops[] = {Zero, Idx};
601        return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
602      }
603      case UnaryOperator::Deref:
604        // The address of a deref is just the value of the expression
605        return Visit(Exp->getSubExpr());
606      }
607      break;
608    }
609    }
610    CGM.WarnUnsupported(E, "constant l-value expression");
611    llvm::Type *Ty = llvm::PointerType::getUnqual(ConvertType(E->getType()));
612    return llvm::UndefValue::get(Ty);
613  }
614
615};
616
617}  // end anonymous namespace.
618
619
620llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
621                                                CodeGenFunction *CGF)
622{
623  QualType type = E->getType().getCanonicalType();
624
625  if (type->isIntegerType()) {
626    llvm::APSInt Value(static_cast<uint32_t>(Context.getTypeSize(type)));
627    if (E->isIntegerConstantExpr(Value, Context)) {
628      return llvm::ConstantInt::get(Value);
629    }
630  }
631
632  return ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
633}
634