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