CGExprConstant.cpp revision 69243825cb5c91ec7207256aa57ae327cfaf8cb2 
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 "clang/Basic/Builtins.h"
21#include "llvm/Constants.h"
22#include "llvm/Function.h"
23#include "llvm/GlobalVariable.h"
24#include "llvm/Support/Compiler.h"
25#include "llvm/Target/TargetData.h"
26using namespace clang;
27using namespace CodeGen;
28
29namespace  {
30class VISIBILITY_HIDDEN ConstExprEmitter :
31  public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
32  CodeGenModule &CGM;
33  CodeGenFunction *CGF;
34public:
35  ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
36    : CGM(cgm), CGF(cgf) {
37  }
38
39  //===--------------------------------------------------------------------===//
40  //                            Visitor Methods
41  //===--------------------------------------------------------------------===//
42
43  llvm::Constant *VisitStmt(Stmt *S) {
44    return 0;
45  }
46
47  llvm::Constant *VisitParenExpr(ParenExpr *PE) {
48    return Visit(PE->getSubExpr());
49  }
50
51  llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
52    return Visit(E->getInitializer());
53  }
54
55  llvm::Constant *VisitCastExpr(CastExpr* E) {
56    // GCC cast to union extension
57    if (E->getType()->isUnionType()) {
58      const llvm::Type *Ty = ConvertType(E->getType());
59      Expr *SubExpr = E->getSubExpr();
60      return EmitUnion(CGM.EmitConstantExpr(SubExpr, SubExpr->getType(), CGF),
61                       Ty);
62    }
63    // Explicit and implicit no-op casts
64    QualType Ty = E->getType(), SubTy = E->getSubExpr()->getType();
65    if (CGM.getContext().hasSameUnqualifiedType(Ty, SubTy)) {
66      return Visit(E->getSubExpr());
67    }
68    return 0;
69  }
70
71  llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
72    return Visit(DAE->getExpr());
73  }
74
75  llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
76    std::vector<llvm::Constant*> Elts;
77    const llvm::ArrayType *AType =
78        cast<llvm::ArrayType>(ConvertType(ILE->getType()));
79    unsigned NumInitElements = ILE->getNumInits();
80    // FIXME: Check for wide strings
81    // FIXME: Check for NumInitElements exactly equal to 1??
82    if (NumInitElements > 0 &&
83        (isa<StringLiteral>(ILE->getInit(0)) ||
84         isa<ObjCEncodeExpr>(ILE->getInit(0))) &&
85        ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
86      return Visit(ILE->getInit(0));
87    const llvm::Type *ElemTy = AType->getElementType();
88    unsigned NumElements = AType->getNumElements();
89
90    // Initialising an array requires us to automatically
91    // initialise any elements that have not been initialised explicitly
92    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
93
94    // Copy initializer elements.
95    unsigned i = 0;
96    bool RewriteType = false;
97    for (; i < NumInitableElts; ++i) {
98      Expr *Init = ILE->getInit(i);
99      llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
100      if (!C)
101        return 0;
102      RewriteType |= (C->getType() != ElemTy);
103      Elts.push_back(C);
104    }
105
106    // Initialize remaining array elements.
107    // FIXME: This doesn't handle member pointers correctly!
108    for (; i < NumElements; ++i)
109      Elts.push_back(CGM.getLLVMContext().getNullValue(ElemTy));
110
111    if (RewriteType) {
112      // FIXME: Try to avoid packing the array
113      std::vector<const llvm::Type*> Types;
114      for (unsigned i = 0; i < Elts.size(); ++i)
115        Types.push_back(Elts[i]->getType());
116      const llvm::StructType *SType = llvm::StructType::get(Types, true);
117      return llvm::ConstantStruct::get(SType, Elts);
118    }
119
120    return llvm::ConstantArray::get(AType, Elts);
121  }
122
123  void InsertBitfieldIntoStruct(std::vector<llvm::Constant*>& Elts,
124                                FieldDecl* Field, Expr* E) {
125    // Calculate the value to insert
126    llvm::Constant *C = CGM.EmitConstantExpr(E, Field->getType(), CGF);
127    if (!C)
128      return;
129
130    llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
131    if (!CI) {
132      CGM.ErrorUnsupported(E, "bitfield initialization");
133      return;
134    }
135    llvm::APInt V = CI->getValue();
136
137    // Calculate information about the relevant field
138    const llvm::Type* Ty = CI->getType();
139    const llvm::TargetData &TD = CGM.getTypes().getTargetData();
140    unsigned size = TD.getTypeAllocSizeInBits(Ty);
141    unsigned fieldOffset = CGM.getTypes().getLLVMFieldNo(Field) * size;
142    CodeGenTypes::BitFieldInfo bitFieldInfo =
143        CGM.getTypes().getBitFieldInfo(Field);
144    fieldOffset += bitFieldInfo.Begin;
145
146    // Find where to start the insertion
147    // FIXME: This is O(n^2) in the number of bit-fields!
148    // FIXME: This won't work if the struct isn't completely packed!
149    unsigned offset = 0, i = 0;
150    while (offset < (fieldOffset & -8))
151      offset += TD.getTypeAllocSizeInBits(Elts[i++]->getType());
152
153    // Advance over 0 sized elements (must terminate in bounds since
154    // the bitfield must have a size).
155    while (TD.getTypeAllocSizeInBits(Elts[i]->getType()) == 0)
156      ++i;
157
158    // Promote the size of V if necessary
159    // FIXME: This should never occur, but currently it can because initializer
160    // constants are cast to bool, and because clang is not enforcing bitfield
161    // width limits.
162    if (bitFieldInfo.Size > V.getBitWidth())
163      V.zext(bitFieldInfo.Size);
164
165    // Insert the bits into the struct
166    // FIXME: This algorthm is only correct on X86!
167    // FIXME: THis algorthm assumes bit-fields only have byte-size elements!
168    unsigned bitsToInsert = bitFieldInfo.Size;
169    unsigned curBits = std::min(8 - (fieldOffset & 7), bitsToInsert);
170    unsigned byte = V.getLoBits(curBits).getZExtValue() << (fieldOffset & 7);
171    do {
172      llvm::Constant* byteC = llvm::ConstantInt::get(llvm::Type::Int8Ty, byte);
173      Elts[i] = llvm::ConstantExpr::getOr(Elts[i], byteC);
174      ++i;
175      V = V.lshr(curBits);
176      bitsToInsert -= curBits;
177
178      if (!bitsToInsert)
179        break;
180
181      curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
182      byte = V.getLoBits(curBits).getZExtValue();
183    } while (true);
184  }
185
186  llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
187    const llvm::StructType *SType =
188        cast<llvm::StructType>(ConvertType(ILE->getType()));
189    RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
190    std::vector<llvm::Constant*> Elts;
191
192    // Initialize the whole structure to zero.
193    // FIXME: This doesn't handle member pointers correctly!
194    for (unsigned i = 0; i < SType->getNumElements(); ++i) {
195      const llvm::Type *FieldTy = SType->getElementType(i);
196      Elts.push_back(CGM.getLLVMContext().getNullValue(FieldTy));
197    }
198
199    // Copy initializer elements. Skip padding fields.
200    unsigned EltNo = 0;  // Element no in ILE
201    bool RewriteType = false;
202    for (RecordDecl::field_iterator Field = RD->field_begin(),
203                                 FieldEnd = RD->field_end();
204         EltNo < ILE->getNumInits() && Field != FieldEnd; ++Field) {
205      if (Field->isBitField()) {
206        if (!Field->getIdentifier())
207          continue;
208        InsertBitfieldIntoStruct(Elts, *Field, ILE->getInit(EltNo));
209      } else {
210        unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(*Field);
211        llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(EltNo),
212                                                 Field->getType(), CGF);
213        if (!C) return 0;
214        RewriteType |= (C->getType() != Elts[FieldNo]->getType());
215        Elts[FieldNo] = C;
216      }
217      EltNo++;
218    }
219
220    if (RewriteType) {
221      // FIXME: Make this work for non-packed structs
222      assert(SType->isPacked() && "Cannot recreate unpacked structs");
223      std::vector<const llvm::Type*> Types;
224      for (unsigned i = 0; i < Elts.size(); ++i)
225        Types.push_back(Elts[i]->getType());
226      SType = llvm::StructType::get(Types, true);
227    }
228
229    return llvm::ConstantStruct::get(SType, Elts);
230  }
231
232  llvm::Constant *EmitUnion(llvm::Constant *C, const llvm::Type *Ty) {
233    if (!C)
234      return 0;
235
236    // Build a struct with the union sub-element as the first member,
237    // and padded to the appropriate size
238    std::vector<llvm::Constant*> Elts;
239    std::vector<const llvm::Type*> Types;
240    Elts.push_back(C);
241    Types.push_back(C->getType());
242    unsigned CurSize = CGM.getTargetData().getTypeAllocSize(C->getType());
243    unsigned TotalSize = CGM.getTargetData().getTypeAllocSize(Ty);
244    while (CurSize < TotalSize) {
245      Elts.push_back(CGM.getLLVMContext().getNullValue(llvm::Type::Int8Ty));
246      Types.push_back(llvm::Type::Int8Ty);
247      CurSize++;
248    }
249
250    // This always generates a packed struct
251    // FIXME: Try to generate an unpacked struct when we can
252    llvm::StructType* STy = llvm::StructType::get(Types, true);
253    return llvm::ConstantStruct::get(STy, Elts);
254  }
255
256  llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
257    const llvm::Type *Ty = ConvertType(ILE->getType());
258
259    FieldDecl* curField = ILE->getInitializedFieldInUnion();
260    if (!curField) {
261      // There's no field to initialize, so value-initialize the union.
262#ifndef NDEBUG
263      // Make sure that it's really an empty and not a failure of
264      // semantic analysis.
265      RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
266      for (RecordDecl::field_iterator Field = RD->field_begin(),
267                                   FieldEnd = RD->field_end();
268           Field != FieldEnd; ++Field)
269        assert(Field->isUnnamedBitfield() && "Only unnamed bitfields allowed");
270#endif
271      return CGM.getLLVMContext().getNullValue(Ty);
272    }
273
274    if (curField->isBitField()) {
275      // Create a dummy struct for bit-field insertion
276      unsigned NumElts = CGM.getTargetData().getTypeAllocSize(Ty);
277      llvm::Constant* NV =
278        CGM.getLLVMContext().getNullValue(llvm::Type::Int8Ty);
279      std::vector<llvm::Constant*> Elts(NumElts, NV);
280
281      InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
282      const llvm::ArrayType *RetTy =
283          llvm::ArrayType::get(NV->getType(), NumElts);
284      return llvm::ConstantArray::get(RetTy, Elts);
285    }
286
287    llvm::Constant *InitElem;
288    if (ILE->getNumInits() > 0) {
289      Expr *Init = ILE->getInit(0);
290      InitElem = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
291    } else {
292      InitElem = CGM.EmitNullConstant(curField->getType());
293    }
294    return EmitUnion(InitElem, Ty);
295  }
296
297  llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
298    const llvm::VectorType *VType =
299        cast<llvm::VectorType>(ConvertType(ILE->getType()));
300    const llvm::Type *ElemTy = VType->getElementType();
301    std::vector<llvm::Constant*> Elts;
302    unsigned NumElements = VType->getNumElements();
303    unsigned NumInitElements = ILE->getNumInits();
304
305    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
306
307    // Copy initializer elements.
308    unsigned i = 0;
309    for (; i < NumInitableElts; ++i) {
310      Expr *Init = ILE->getInit(i);
311      llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
312      if (!C)
313        return 0;
314      Elts.push_back(C);
315    }
316
317    for (; i < NumElements; ++i)
318      Elts.push_back(CGM.getLLVMContext().getNullValue(ElemTy));
319
320    return llvm::ConstantVector::get(VType, Elts);
321  }
322
323  llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
324    return CGM.EmitNullConstant(E->getType());
325  }
326
327  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
328    if (ILE->getType()->isScalarType()) {
329      // We have a scalar in braces. Just use the first element.
330      if (ILE->getNumInits() > 0) {
331        Expr *Init = ILE->getInit(0);
332        return CGM.EmitConstantExpr(Init, Init->getType(), CGF);
333      }
334      return CGM.EmitNullConstant(ILE->getType());
335    }
336
337    if (ILE->getType()->isArrayType())
338      return EmitArrayInitialization(ILE);
339
340    if (ILE->getType()->isStructureType())
341      return EmitStructInitialization(ILE);
342
343    if (ILE->getType()->isUnionType())
344      return EmitUnionInitialization(ILE);
345
346    if (ILE->getType()->isVectorType())
347      return EmitVectorInitialization(ILE);
348
349    assert(0 && "Unable to handle InitListExpr");
350    // Get rid of control reaches end of void function warning.
351    // Not reached.
352    return 0;
353  }
354
355  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
356    assert(!E->getType()->isPointerType() && "Strings are always arrays");
357
358    // This must be a string initializing an array in a static initializer.
359    // Don't emit it as the address of the string, emit the string data itself
360    // as an inline array.
361    return llvm::ConstantArray::get(CGM.GetStringForStringLiteral(E), false);
362  }
363
364  llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
365    // This must be an @encode initializing an array in a static initializer.
366    // Don't emit it as the address of the string, emit the string data itself
367    // as an inline array.
368    std::string Str;
369    CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
370    const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
371
372    // Resize the string to the right size, adding zeros at the end, or
373    // truncating as needed.
374    Str.resize(CAT->getSize().getZExtValue(), '\0');
375    return llvm::ConstantArray::get(Str, false);
376  }
377
378  llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
379    return Visit(E->getSubExpr());
380  }
381
382  // Utility methods
383  const llvm::Type *ConvertType(QualType T) {
384    return CGM.getTypes().ConvertType(T);
385  }
386
387public:
388  llvm::Constant *EmitLValue(Expr *E) {
389    switch (E->getStmtClass()) {
390    default: break;
391    case Expr::CompoundLiteralExprClass: {
392      // Note that due to the nature of compound literals, this is guaranteed
393      // to be the only use of the variable, so we just generate it here.
394      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
395      llvm::Constant* C = Visit(CLE->getInitializer());
396      // FIXME: "Leaked" on failure.
397      if (C)
398        C = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
399                                     E->getType().isConstQualified(),
400                                     llvm::GlobalValue::InternalLinkage,
401                                     C, ".compoundliteral");
402      return C;
403    }
404    case Expr::DeclRefExprClass:
405    case Expr::QualifiedDeclRefExprClass: {
406      NamedDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
407      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
408        return CGM.GetAddrOfFunction(GlobalDecl(FD));
409      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
410        // We can never refer to a variable with local storage.
411        if (!VD->hasLocalStorage()) {
412          if (VD->isFileVarDecl() || VD->hasExternalStorage())
413            return CGM.GetAddrOfGlobalVar(VD);
414          else if (VD->isBlockVarDecl()) {
415            assert(CGF && "Can't access static local vars without CGF");
416            return CGF->GetAddrOfStaticLocalVar(VD);
417          }
418        }
419      }
420      break;
421    }
422    case Expr::StringLiteralClass:
423      return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
424    case Expr::ObjCEncodeExprClass:
425      return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
426    case Expr::ObjCStringLiteralClass: {
427      ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
428      llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(SL);
429      return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
430    }
431    case Expr::PredefinedExprClass: {
432      // __func__/__FUNCTION__ -> "".  __PRETTY_FUNCTION__ -> "top level".
433      std::string Str;
434      if (cast<PredefinedExpr>(E)->getIdentType() ==
435          PredefinedExpr::PrettyFunction)
436        Str = "top level";
437
438      return CGM.GetAddrOfConstantCString(Str, ".tmp");
439    }
440    case Expr::AddrLabelExprClass: {
441      assert(CGF && "Invalid address of label expression outside function.");
442      unsigned id = CGF->GetIDForAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
443      llvm::Constant *C = llvm::ConstantInt::get(llvm::Type::Int32Ty, id);
444      return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
445    }
446    case Expr::CallExprClass: {
447      CallExpr* CE = cast<CallExpr>(E);
448      if (CE->isBuiltinCall(CGM.getContext()) !=
449            Builtin::BI__builtin___CFStringMakeConstantString)
450        break;
451      const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
452      const StringLiteral *Literal = cast<StringLiteral>(Arg);
453      // FIXME: need to deal with UCN conversion issues.
454      return CGM.GetAddrOfConstantCFString(Literal);
455    }
456    case Expr::BlockExprClass: {
457      std::string FunctionName;
458      if (CGF)
459        FunctionName = CGF->CurFn->getName();
460      else
461        FunctionName = "global";
462
463      return CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
464    }
465    }
466
467    return 0;
468  }
469};
470
471}  // end anonymous namespace.
472
473llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
474                                                QualType DestType,
475                                                CodeGenFunction *CGF) {
476  Expr::EvalResult Result;
477
478  bool Success = false;
479
480  if (DestType->isReferenceType())
481    Success = E->EvaluateAsLValue(Result, Context);
482  else
483    Success = E->Evaluate(Result, Context);
484
485  if (Success) {
486    assert(!Result.HasSideEffects &&
487           "Constant expr should not have any side effects!");
488    switch (Result.Val.getKind()) {
489    case APValue::Uninitialized:
490      assert(0 && "Constant expressions should be initialized.");
491      return 0;
492    case APValue::LValue: {
493      const llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
494      llvm::Constant *Offset =
495        llvm::ConstantInt::get(llvm::Type::Int64Ty,
496                               Result.Val.getLValueOffset());
497
498      llvm::Constant *C;
499      if (const Expr *LVBase = Result.Val.getLValueBase()) {
500        C = ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
501
502        // Apply offset if necessary.
503        if (!Offset->isNullValue()) {
504          const llvm::Type *Type =
505            llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
506          llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
507          Casted = llvm::ConstantExpr::getGetElementPtr(Casted, &Offset, 1);
508          C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
509        }
510
511        // Convert to the appropriate type; this could be an lvalue for
512        // an integer.
513        if (isa<llvm::PointerType>(DestTy))
514          return llvm::ConstantExpr::getBitCast(C, DestTy);
515
516        return llvm::ConstantExpr::getPtrToInt(C, DestTy);
517      } else {
518        C = Offset;
519
520        // Convert to the appropriate type; this could be an lvalue for
521        // an integer.
522        if (isa<llvm::PointerType>(DestTy))
523          return llvm::ConstantExpr::getIntToPtr(C, DestTy);
524
525        // If the types don't match this should only be a truncate.
526        if (C->getType() != DestTy)
527          return llvm::ConstantExpr::getTrunc(C, DestTy);
528
529        return C;
530      }
531    }
532    case APValue::Int: {
533      llvm::Constant *C = llvm::ConstantInt::get(Result.Val.getInt());
534
535      if (C->getType() == llvm::Type::Int1Ty) {
536        const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
537        C = llvm::ConstantExpr::getZExt(C, BoolTy);
538      }
539      return C;
540    }
541    case APValue::ComplexInt: {
542      llvm::Constant *Complex[2];
543
544      Complex[0] = llvm::ConstantInt::get(Result.Val.getComplexIntReal());
545      Complex[1] = llvm::ConstantInt::get(Result.Val.getComplexIntImag());
546
547      return llvm::ConstantStruct::get(Complex, 2);
548    }
549    case APValue::Float:
550      return llvm::ConstantFP::get(Result.Val.getFloat());
551    case APValue::ComplexFloat: {
552      llvm::Constant *Complex[2];
553
554      Complex[0] = llvm::ConstantFP::get(Result.Val.getComplexFloatReal());
555      Complex[1] = llvm::ConstantFP::get(Result.Val.getComplexFloatImag());
556
557      return llvm::ConstantStruct::get(Complex, 2);
558    }
559    case APValue::Vector: {
560      llvm::SmallVector<llvm::Constant *, 4> Inits;
561      unsigned NumElts = Result.Val.getVectorLength();
562
563      for (unsigned i = 0; i != NumElts; ++i) {
564        APValue &Elt = Result.Val.getVectorElt(i);
565        if (Elt.isInt())
566          Inits.push_back(llvm::ConstantInt::get(Elt.getInt()));
567        else
568          Inits.push_back(llvm::ConstantFP::get(Elt.getFloat()));
569      }
570      return llvm::ConstantVector::get(&Inits[0], Inits.size());
571    }
572    }
573  }
574
575  llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
576  if (C && C->getType() == llvm::Type::Int1Ty) {
577    const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
578    C = llvm::ConstantExpr::getZExt(C, BoolTy);
579  }
580  return C;
581}
582
583llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
584  // Always return an LLVM null constant for now; this will change when we
585  // get support for IRGen of member pointers.
586  return getLLVMContext().getNullValue(getTypes().ConvertType(T));
587}
588