CGExprConstant.cpp revision 8a2b4b1c5b960710db95e9b296d9a600aee37c00 
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    if (CGM.getContext().getCanonicalType(E->getSubExpr()->getType()) ==
63        CGM.getContext().getCanonicalType(E->getType())) {
64      return Visit(E->getSubExpr());
65    }
66    return 0;
67  }
68
69  llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
70    return Visit(DAE->getExpr());
71  }
72
73  llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
74    std::vector<llvm::Constant*> Elts;
75    const llvm::ArrayType *AType =
76        cast<llvm::ArrayType>(ConvertType(ILE->getType()));
77    unsigned NumInitElements = ILE->getNumInits();
78    // FIXME: Check for wide strings
79    // FIXME: Check for NumInitElements exactly equal to 1??
80    if (NumInitElements > 0 &&
81        (isa<StringLiteral>(ILE->getInit(0)) ||
82         isa<ObjCEncodeExpr>(ILE->getInit(0))) &&
83        ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
84      return Visit(ILE->getInit(0));
85    const llvm::Type *ElemTy = AType->getElementType();
86    unsigned NumElements = AType->getNumElements();
87
88    // Initialising an array requires us to automatically
89    // initialise any elements that have not been initialised explicitly
90    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
91
92    // Copy initializer elements.
93    unsigned i = 0;
94    bool RewriteType = false;
95    for (; i < NumInitableElts; ++i) {
96      llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(i), CGF);
97      if (!C)
98        return 0;
99      RewriteType |= (C->getType() != ElemTy);
100      Elts.push_back(C);
101    }
102
103    // Initialize remaining array elements.
104    for (; i < NumElements; ++i)
105      Elts.push_back(llvm::Constant::getNullValue(ElemTy));
106
107    if (RewriteType) {
108      // FIXME: Try to avoid packing the array
109      std::vector<const llvm::Type*> Types;
110      for (unsigned i = 0; i < Elts.size(); ++i)
111        Types.push_back(Elts[i]->getType());
112      const llvm::StructType *SType = llvm::StructType::get(Types, true);
113      return llvm::ConstantStruct::get(SType, Elts);
114    }
115
116    return llvm::ConstantArray::get(AType, Elts);
117  }
118
119  void InsertBitfieldIntoStruct(std::vector<llvm::Constant*>& Elts,
120                                FieldDecl* Field, Expr* E) {
121    // Calculate the value to insert
122    llvm::Constant *C = CGM.EmitConstantExpr(E, CGF);
123    if (!C)
124      return;
125
126    llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
127    if (!CI) {
128      CGM.ErrorUnsupported(E, "bitfield initialization");
129      return;
130    }
131    llvm::APInt V = CI->getValue();
132
133    // Calculate information about the relevant field
134    const llvm::Type* Ty = CI->getType();
135    const llvm::TargetData &TD = CGM.getTypes().getTargetData();
136    unsigned size = TD.getTypePaddedSizeInBits(Ty);
137    unsigned fieldOffset = CGM.getTypes().getLLVMFieldNo(Field) * size;
138    CodeGenTypes::BitFieldInfo bitFieldInfo =
139        CGM.getTypes().getBitFieldInfo(Field);
140    fieldOffset += bitFieldInfo.Begin;
141
142    // Find where to start the insertion
143    // FIXME: This is O(n^2) in the number of bit-fields!
144    // FIXME: This won't work if the struct isn't completely packed!
145    unsigned offset = 0, i = 0;
146    while (offset < (fieldOffset & -8))
147      offset += TD.getTypePaddedSizeInBits(Elts[i++]->getType());
148
149    // Advance over 0 sized elements (must terminate in bounds since
150    // the bitfield must have a size).
151    while (TD.getTypePaddedSizeInBits(Elts[i]->getType()) == 0)
152      ++i;
153
154    // Promote the size of V if necessary
155    // FIXME: This should never occur, but currently it can because
156    // initializer constants are cast to bool, and because clang is
157    // not enforcing bitfield width limits.
158    if (bitFieldInfo.Size > V.getBitWidth())
159      V.zext(bitFieldInfo.Size);
160
161    // Insert the bits into the struct
162    // FIXME: This algorthm is only correct on X86!
163    // FIXME: THis algorthm assumes bit-fields only have byte-size elements!
164    unsigned bitsToInsert = bitFieldInfo.Size;
165    unsigned curBits = std::min(8 - (fieldOffset & 7), bitsToInsert);
166    unsigned byte = V.getLoBits(curBits).getZExtValue() << (fieldOffset & 7);
167    do {
168      llvm::Constant* byteC = llvm::ConstantInt::get(llvm::Type::Int8Ty, byte);
169      Elts[i] = llvm::ConstantExpr::getOr(Elts[i], byteC);
170      ++i;
171      V = V.lshr(curBits);
172      bitsToInsert -= curBits;
173
174      if (!bitsToInsert)
175        break;
176
177      curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
178      byte = V.getLoBits(curBits).getZExtValue();
179    } while (true);
180  }
181
182  llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
183    const llvm::StructType *SType =
184        cast<llvm::StructType>(ConvertType(ILE->getType()));
185    RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
186    std::vector<llvm::Constant*> Elts;
187
188    // Initialize the whole structure to zero.
189    for (unsigned i = 0; i < SType->getNumElements(); ++i) {
190      const llvm::Type *FieldTy = SType->getElementType(i);
191      Elts.push_back(llvm::Constant::getNullValue(FieldTy));
192    }
193
194    // Copy initializer elements. Skip padding fields.
195    unsigned EltNo = 0;  // Element no in ILE
196    int FieldNo = 0; // Field no in RecordDecl
197    bool RewriteType = false;
198    for (RecordDecl::field_iterator Field = RD->field_begin(),
199                                 FieldEnd = RD->field_end();
200         EltNo < ILE->getNumInits() && Field != FieldEnd; ++Field) {
201      FieldNo++;
202      if (!Field->getIdentifier())
203        continue;
204
205      if (Field->isBitField()) {
206        InsertBitfieldIntoStruct(Elts, *Field, ILE->getInit(EltNo));
207      } else {
208        unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(*Field);
209        llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(EltNo), CGF);
210        if (!C) return 0;
211        RewriteType |= (C->getType() != Elts[FieldNo]->getType());
212        Elts[FieldNo] = C;
213      }
214      EltNo++;
215    }
216
217    if (RewriteType) {
218      // FIXME: Make this work for non-packed structs
219      assert(SType->isPacked() && "Cannot recreate unpacked structs");
220      std::vector<const llvm::Type*> Types;
221      for (unsigned i = 0; i < Elts.size(); ++i)
222        Types.push_back(Elts[i]->getType());
223      SType = llvm::StructType::get(Types, true);
224    }
225
226    return llvm::ConstantStruct::get(SType, Elts);
227  }
228
229  llvm::Constant *EmitUnion(llvm::Constant *C, const llvm::Type *Ty) {
230    if (!C)
231      return 0;
232
233    // Build a struct with the union sub-element as the first member,
234    // and padded to the appropriate size
235    std::vector<llvm::Constant*> Elts;
236    std::vector<const llvm::Type*> Types;
237    Elts.push_back(C);
238    Types.push_back(C->getType());
239    unsigned CurSize = CGM.getTargetData().getTypePaddedSize(C->getType());
240    unsigned TotalSize = CGM.getTargetData().getTypePaddedSize(Ty);
241    while (CurSize < TotalSize) {
242      Elts.push_back(llvm::Constant::getNullValue(llvm::Type::Int8Ty));
243      Types.push_back(llvm::Type::Int8Ty);
244      CurSize++;
245    }
246
247    // This always generates a packed struct
248    // FIXME: Try to generate an unpacked struct when we can
249    llvm::StructType* STy = llvm::StructType::get(Types, true);
250    return llvm::ConstantStruct::get(STy, Elts);
251  }
252
253  llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
254    const llvm::Type *Ty = ConvertType(ILE->getType());
255
256    // If this is an empty initializer list, we value-initialize the
257    // union.
258    if (ILE->getNumInits() == 0)
259      return llvm::Constant::getNullValue(Ty);
260
261    FieldDecl* curField = ILE->getInitializedFieldInUnion();
262    if (!curField) {
263      // There's no field to initialize, so value-initialize the union.
264#ifndef NDEBUG
265      // Make sure that it's really an empty and not a failure of
266      // semantic analysis.
267      RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
268      for (RecordDecl::field_iterator Field = RD->field_begin(),
269                                   FieldEnd = RD->field_end();
270           Field != FieldEnd; ++Field)
271        assert(Field->isUnnamedBitfield() && "Only unnamed bitfields allowed");
272#endif
273      return llvm::Constant::getNullValue(Ty);
274    }
275
276    if (curField->isBitField()) {
277      // Create a dummy struct for bit-field insertion
278      unsigned NumElts = CGM.getTargetData().getTypePaddedSize(Ty) / 8;
279      llvm::Constant* NV = llvm::Constant::getNullValue(llvm::Type::Int8Ty);
280      std::vector<llvm::Constant*> Elts(NumElts, NV);
281
282      InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
283      const llvm::ArrayType *RetTy =
284          llvm::ArrayType::get(NV->getType(), NumElts);
285      return llvm::ConstantArray::get(RetTy, Elts);
286    }
287
288    return EmitUnion(CGM.EmitConstantExpr(ILE->getInit(0), CGF), Ty);
289  }
290
291  llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
292    const llvm::VectorType *VType =
293        cast<llvm::VectorType>(ConvertType(ILE->getType()));
294    const llvm::Type *ElemTy = VType->getElementType();
295    std::vector<llvm::Constant*> Elts;
296    unsigned NumElements = VType->getNumElements();
297    unsigned NumInitElements = ILE->getNumInits();
298
299    unsigned NumInitableElts = std::min(NumInitElements, NumElements);
300
301    // Copy initializer elements.
302    unsigned i = 0;
303    for (; i < NumInitableElts; ++i) {
304      llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(i), CGF);
305      if (!C)
306        return 0;
307      Elts.push_back(C);
308    }
309
310    for (; i < NumElements; ++i)
311      Elts.push_back(llvm::Constant::getNullValue(ElemTy));
312
313    return llvm::ConstantVector::get(VType, Elts);
314  }
315
316  llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
317    const llvm::Type* RetTy = CGM.getTypes().ConvertType(E->getType());
318    return llvm::Constant::getNullValue(RetTy);
319  }
320
321  llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
322    if (ILE->getType()->isScalarType()) {
323      // We have a scalar in braces. Just use the first element.
324      if (ILE->getNumInits() > 0)
325        return CGM.EmitConstantExpr(ILE->getInit(0), CGF);
326
327      const llvm::Type* RetTy = CGM.getTypes().ConvertType(ILE->getType());
328      return llvm::Constant::getNullValue(RetTy);
329    }
330
331    if (ILE->getType()->isArrayType())
332      return EmitArrayInitialization(ILE);
333
334    if (ILE->getType()->isStructureType())
335      return EmitStructInitialization(ILE);
336
337    if (ILE->getType()->isUnionType())
338      return EmitUnionInitialization(ILE);
339
340    if (ILE->getType()->isVectorType())
341      return EmitVectorInitialization(ILE);
342
343    assert(0 && "Unable to handle InitListExpr");
344    // Get rid of control reaches end of void function warning.
345    // Not reached.
346    return 0;
347  }
348
349  llvm::Constant *VisitStringLiteral(StringLiteral *E) {
350    assert(!E->getType()->isPointerType() && "Strings are always arrays");
351
352    // This must be a string initializing an array in a static initializer.
353    // Don't emit it as the address of the string, emit the string data itself
354    // as an inline array.
355    return llvm::ConstantArray::get(CGM.GetStringForStringLiteral(E), false);
356  }
357
358  llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
359    // This must be an @encode initializing an array in a static initializer.
360    // Don't emit it as the address of the string, emit the string data itself
361    // as an inline array.
362    std::string Str;
363    CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
364    const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
365
366    // Resize the string to the right size, adding zeros at the end, or
367    // truncating as needed.
368    Str.resize(CAT->getSize().getZExtValue(), '\0');
369    return llvm::ConstantArray::get(Str, false);
370  }
371
372  llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
373    return Visit(E->getSubExpr());
374  }
375
376  // Utility methods
377  const llvm::Type *ConvertType(QualType T) {
378    return CGM.getTypes().ConvertType(T);
379  }
380
381public:
382  llvm::Constant *EmitLValue(Expr *E) {
383    switch (E->getStmtClass()) {
384    default: break;
385    case Expr::CompoundLiteralExprClass: {
386      // Note that due to the nature of compound literals, this is guaranteed
387      // to be the only use of the variable, so we just generate it here.
388      CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
389      llvm::Constant* C = Visit(CLE->getInitializer());
390      // FIXME: "Leaked" on failure.
391      if (C)
392        C = new llvm::GlobalVariable(C->getType(),
393                                     E->getType().isConstQualified(),
394                                     llvm::GlobalValue::InternalLinkage,
395                                     C, ".compoundliteral", &CGM.getModule());
396      return C;
397    }
398    case Expr::DeclRefExprClass:
399    case Expr::QualifiedDeclRefExprClass: {
400      NamedDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
401      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
402        return CGM.GetAddrOfFunction(FD);
403      if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
404        // We can never refer to a variable with local storage.
405        if (!VD->hasLocalStorage()) {
406          if (VD->isFileVarDecl() || VD->hasExternalStorage())
407            return CGM.GetAddrOfGlobalVar(VD);
408          else if (VD->isBlockVarDecl()) {
409            assert(CGF && "Can't access static local vars without CGF");
410            return CGF->GetAddrOfStaticLocalVar(VD);
411          }
412        }
413      }
414      break;
415    }
416    case Expr::StringLiteralClass:
417      return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
418    case Expr::ObjCEncodeExprClass:
419      return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
420    case Expr::ObjCStringLiteralClass: {
421      ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
422      std::string S(SL->getString()->getStrData(),
423                    SL->getString()->getByteLength());
424      llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(S);
425      return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
426    }
427    case Expr::PredefinedExprClass: {
428      // __func__/__FUNCTION__ -> "".  __PRETTY_FUNCTION__ -> "top level".
429      std::string Str;
430      if (cast<PredefinedExpr>(E)->getIdentType() ==
431          PredefinedExpr::PrettyFunction)
432        Str = "top level";
433
434      return CGM.GetAddrOfConstantCString(Str, ".tmp");
435    }
436    case Expr::AddrLabelExprClass: {
437      assert(CGF && "Invalid address of label expression outside function.");
438      unsigned id = CGF->GetIDForAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
439      llvm::Constant *C = llvm::ConstantInt::get(llvm::Type::Int32Ty, id);
440      return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
441    }
442    case Expr::CallExprClass: {
443      CallExpr* CE = cast<CallExpr>(E);
444      if (CE->isBuiltinCall(CGM.getContext()) !=
445            Builtin::BI__builtin___CFStringMakeConstantString)
446        break;
447      const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
448      const StringLiteral *Literal = cast<StringLiteral>(Arg);
449      std::string S(Literal->getStrData(), Literal->getByteLength());
450      return CGM.GetAddrOfConstantCFString(S);
451    }
452    case Expr::BlockExprClass: {
453      BlockExpr *B = cast<BlockExpr>(E);
454      if (!B->hasBlockDeclRefExprs())
455        return cast<llvm::Constant>(CGF->BuildBlockLiteralTmp(B));
456    }
457    }
458
459    return 0;
460  }
461};
462
463}  // end anonymous namespace.
464
465llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
466                                                CodeGenFunction *CGF) {
467  Expr::EvalResult Result;
468
469  if (E->Evaluate(Result, Context)) {
470    assert(!Result.HasSideEffects &&
471           "Constant expr should not have any side effects!");
472    switch (Result.Val.getKind()) {
473    case APValue::Uninitialized:
474      assert(0 && "Constant expressions should be initialized.");
475      return 0;
476    case APValue::LValue: {
477      const llvm::Type *DestType = getTypes().ConvertTypeForMem(E->getType());
478      llvm::Constant *Offset =
479        llvm::ConstantInt::get(llvm::Type::Int64Ty,
480                               Result.Val.getLValueOffset());
481
482      llvm::Constant *C;
483      if (const Expr *LVBase = Result.Val.getLValueBase()) {
484        C = ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
485
486        // Apply offset if necessary.
487        if (!Offset->isNullValue()) {
488          const llvm::Type *Type =
489            llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
490          llvm::Constant *Casted = llvm::ConstantExpr::getBitCast(C, Type);
491          Casted = llvm::ConstantExpr::getGetElementPtr(Casted, &Offset, 1);
492          C = llvm::ConstantExpr::getBitCast(Casted, C->getType());
493        }
494
495        // Convert to the appropriate type; this could be an lvalue for
496        // an integer.
497        if (isa<llvm::PointerType>(DestType))
498          return llvm::ConstantExpr::getBitCast(C, DestType);
499
500        return llvm::ConstantExpr::getPtrToInt(C, DestType);
501      } else {
502        C = Offset;
503
504        // Convert to the appropriate type; this could be an lvalue for
505        // an integer.
506        if (isa<llvm::PointerType>(DestType))
507          return llvm::ConstantExpr::getIntToPtr(C, DestType);
508
509        // If the types don't match this should only be a truncate.
510        if (C->getType() != DestType)
511          return llvm::ConstantExpr::getTrunc(C, DestType);
512
513        return C;
514      }
515    }
516    case APValue::Int: {
517      llvm::Constant *C = llvm::ConstantInt::get(Result.Val.getInt());
518
519      if (C->getType() == llvm::Type::Int1Ty) {
520        const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
521        C = llvm::ConstantExpr::getZExt(C, BoolTy);
522      }
523      return C;
524    }
525    case APValue::ComplexInt: {
526      llvm::Constant *Complex[2];
527
528      Complex[0] = llvm::ConstantInt::get(Result.Val.getComplexIntReal());
529      Complex[1] = llvm::ConstantInt::get(Result.Val.getComplexIntImag());
530
531      return llvm::ConstantStruct::get(Complex, 2);
532    }
533    case APValue::Float:
534      return llvm::ConstantFP::get(Result.Val.getFloat());
535    case APValue::ComplexFloat: {
536      llvm::Constant *Complex[2];
537
538      Complex[0] = llvm::ConstantFP::get(Result.Val.getComplexFloatReal());
539      Complex[1] = llvm::ConstantFP::get(Result.Val.getComplexFloatImag());
540
541      return llvm::ConstantStruct::get(Complex, 2);
542    }
543    case APValue::Vector: {
544      llvm::SmallVector<llvm::Constant *, 4> Inits;
545      unsigned NumElts = Result.Val.getVectorLength();
546
547      for (unsigned i = 0; i != NumElts; ++i) {
548        APValue &Elt = Result.Val.getVectorElt(i);
549        if (Elt.isInt())
550          Inits.push_back(llvm::ConstantInt::get(Elt.getInt()));
551        else
552          Inits.push_back(llvm::ConstantFP::get(Elt.getFloat()));
553      }
554      return llvm::ConstantVector::get(&Inits[0], Inits.size());
555    }
556    }
557  }
558
559  llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
560  if (C && C->getType() == llvm::Type::Int1Ty) {
561    const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
562    C = llvm::ConstantExpr::getZExt(C, BoolTy);
563  }
564  return C;
565}
566