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 #define USE_TRY_EVALUATE
29 
30 namespace  {
31 class VISIBILITY_HIDDEN ConstExprEmitter :
32   public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
33   CodeGenModule &CGM;
34   CodeGenFunction *CGF;
35 public:
36   ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
37     : CGM(cgm), CGF(cgf) {
38   }
39 
40   //===--------------------------------------------------------------------===//
41   //                            Visitor Methods
42   //===--------------------------------------------------------------------===//
43 
44   llvm::Constant *VisitStmt(Stmt *S) {
45     CGM.ErrorUnsupported(S, "constant expression");
46     QualType T = cast<Expr>(S)->getType();
47     return llvm::UndefValue::get(CGM.getTypes().ConvertType(T));
48   }
49 
50   llvm::Constant *VisitParenExpr(ParenExpr *PE) {
51     return Visit(PE->getSubExpr());
52   }
53 
54 #ifndef USE_TRY_EVALUATE
55   // Leaves
56   llvm::Constant *VisitIntegerLiteral(const IntegerLiteral *E) {
57     return llvm::ConstantInt::get(E->getValue());
58   }
59   llvm::Constant *VisitFloatingLiteral(const FloatingLiteral *E) {
60     return llvm::ConstantFP::get(E->getValue());
61   }
62   llvm::Constant *VisitCharacterLiteral(const CharacterLiteral *E) {
63     return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
64   }
65   llvm::Constant *VisitCXXBoolLiteralExpr(const CXXBoolLiteralExpr *E) {
66     return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
67   }
68   llvm::Constant *VisitCXXZeroInitValueExpr(const CXXZeroInitValueExpr *E) {
69     return llvm::Constant::getNullValue(ConvertType(E->getType()));
70   }
71 #endif
72   llvm::Constant *VisitObjCStringLiteral(const ObjCStringLiteral *E) {
73     std::string S(E->getString()->getStrData(),
74                   E->getString()->getByteLength());
75     llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(S);
76     return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
77   }
78 
79   llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
80     return Visit(E->getInitializer());
81   }
82 
83   llvm::Constant *VisitCastExpr(CastExpr* E) {
84     llvm::Constant *C = Visit(E->getSubExpr());
85 
86     return EmitConversion(C, E->getSubExpr()->getType(), E->getType());
87   }
88 
89   llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
90     return Visit(DAE->getExpr());
91   }
92 
93   llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
94     std::vector<llvm::Constant*> Elts;
95     const llvm::ArrayType *AType =
96         cast<llvm::ArrayType>(ConvertType(ILE->getType()));
97     unsigned NumInitElements = ILE->getNumInits();
98     // FIXME: Check for wide strings
99     if (NumInitElements > 0 && isa<StringLiteral>(ILE->getInit(0)) &&
100         ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
101       return Visit(ILE->getInit(0));
102     const llvm::Type *ElemTy = AType->getElementType();
103     unsigned NumElements = AType->getNumElements();
104 
105     // Initialising an array requires us to automatically
106     // initialise any elements that have not been initialised explicitly
107     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
108 
109     // Copy initializer elements.
110     unsigned i = 0;
111     bool RewriteType = false;
112     for (; i < NumInitableElts; ++i) {
113       llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(i), CGF);
114       RewriteType |= (C->getType() != ElemTy);
115       Elts.push_back(C);
116     }
117 
118     // Initialize remaining array elements.
119     for (; i < NumElements; ++i)
120       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
121 
122     if (RewriteType) {
123       // FIXME: Try to avoid packing the array
124       std::vector<const llvm::Type*> Types;
125       for (unsigned i = 0; i < Elts.size(); ++i)
126         Types.push_back(Elts[i]->getType());
127       const llvm::StructType *SType = llvm::StructType::get(Types, true);
128       return llvm::ConstantStruct::get(SType, Elts);
129     }
130 
131     return llvm::ConstantArray::get(AType, Elts);
132   }
133 
134   void InsertBitfieldIntoStruct(std::vector<llvm::Constant*>& Elts,
135                                 FieldDecl* Field, Expr* E) {
136     // Calculate the value to insert
137     llvm::Constant *C = CGM.EmitConstantExpr(E, CGF);
138     llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
139     if (!CI) {
140       CGM.ErrorUnsupported(E, "bitfield initialization");
141       return;
142     }
143     llvm::APInt V = CI->getValue();
144 
145     // Calculate information about the relevant field
146     const llvm::Type* Ty = CI->getType();
147     const llvm::TargetData &TD = CGM.getTypes().getTargetData();
148     unsigned size = TD.getTypeStoreSizeInBits(Ty);
149     unsigned fieldOffset = CGM.getTypes().getLLVMFieldNo(Field) * size;
150     CodeGenTypes::BitFieldInfo bitFieldInfo =
151         CGM.getTypes().getBitFieldInfo(Field);
152     fieldOffset += bitFieldInfo.Begin;
153 
154     // Find where to start the insertion
155     // FIXME: This is O(n^2) in the number of bit-fields!
156     // FIXME: This won't work if the struct isn't completely packed!
157     unsigned offset = 0, i = 0;
158     while (offset < (fieldOffset & -8))
159       offset += TD.getTypeStoreSizeInBits(Elts[i++]->getType());
160 
161     // Advance over 0 sized elements (must terminate in bounds since
162     // the bitfield must have a size).
163     while (TD.getTypeStoreSizeInBits(Elts[i]->getType()) == 0)
164       ++i;
165 
166     // Promote the size of V if necessary
167     // FIXME: This should never occur, but currently it can because
168     // initializer constants are cast to bool, and because clang is
169     // not enforcing bitfield width limits.
170     if (bitFieldInfo.Size > V.getBitWidth())
171       V.zext(bitFieldInfo.Size);
172 
173     // Insert the bits into the struct
174     // FIXME: This algorthm is only correct on X86!
175     // FIXME: THis algorthm assumes bit-fields only have byte-size elements!
176     unsigned bitsToInsert = bitFieldInfo.Size;
177     unsigned curBits = std::min(8 - (fieldOffset & 7), bitsToInsert);
178     unsigned byte = V.getLoBits(curBits).getZExtValue() << (fieldOffset & 7);
179     do {
180       llvm::Constant* byteC = llvm::ConstantInt::get(llvm::Type::Int8Ty, byte);
181       Elts[i] = llvm::ConstantExpr::getOr(Elts[i], byteC);
182       ++i;
183       V = V.lshr(curBits);
184       bitsToInsert -= curBits;
185 
186       if (!bitsToInsert)
187         break;
188 
189       curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
190       byte = V.getLoBits(curBits).getZExtValue();
191     } while (true);
192   }
193 
194   llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
195     const llvm::StructType *SType =
196         cast<llvm::StructType>(ConvertType(ILE->getType()));
197     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
198     std::vector<llvm::Constant*> Elts;
199 
200     // Initialize the whole structure to zero.
201     for (unsigned i = 0; i < SType->getNumElements(); ++i) {
202       const llvm::Type *FieldTy = SType->getElementType(i);
203       Elts.push_back(llvm::Constant::getNullValue(FieldTy));
204     }
205 
206     // Copy initializer elements. Skip padding fields.
207     unsigned EltNo = 0;  // Element no in ILE
208     int FieldNo = 0; // Field no in RecordDecl
209     bool RewriteType = false;
210     while (EltNo < ILE->getNumInits() && FieldNo < RD->getNumMembers()) {
211       FieldDecl* curField = RD->getMember(FieldNo);
212       FieldNo++;
213       if (!curField->getIdentifier())
214         continue;
215 
216       if (curField->isBitField()) {
217         InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(EltNo));
218       } else {
219         unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(curField);
220         llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(EltNo), CGF);
221         RewriteType |= (C->getType() != Elts[FieldNo]->getType());
222         Elts[FieldNo] = C;
223       }
224       EltNo++;
225     }
226 
227     if (RewriteType) {
228       // FIXME: Make this work for non-packed structs
229       assert(SType->isPacked() && "Cannot recreate unpacked structs");
230       std::vector<const llvm::Type*> Types;
231       for (unsigned i = 0; i < Elts.size(); ++i)
232         Types.push_back(Elts[i]->getType());
233       SType = llvm::StructType::get(Types, true);
234     }
235 
236     return llvm::ConstantStruct::get(SType, Elts);
237   }
238 
239   llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
240     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
241     const llvm::Type *Ty = ConvertType(ILE->getType());
242 
243     // Find the field decl we're initializing, if any
244     int FieldNo = 0; // Field no in RecordDecl
245     FieldDecl* curField = 0;
246     while (FieldNo < RD->getNumMembers()) {
247       curField = RD->getMember(FieldNo);
248       FieldNo++;
249       if (curField->getIdentifier())
250         break;
251     }
252 
253     if (!curField || !curField->getIdentifier() || ILE->getNumInits() == 0)
254       return llvm::Constant::getNullValue(Ty);
255 
256     if (curField->isBitField()) {
257       // Create a dummy struct for bit-field insertion
258       unsigned NumElts = CGM.getTargetData().getABITypeSize(Ty) / 8;
259       llvm::Constant* NV = llvm::Constant::getNullValue(llvm::Type::Int8Ty);
260       std::vector<llvm::Constant*> Elts(NumElts, NV);
261 
262       InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
263       const llvm::ArrayType *RetTy =
264           llvm::ArrayType::get(NV->getType(), NumElts);
265       return llvm::ConstantArray::get(RetTy, Elts);
266     }
267 
268     llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(0), CGF);
269 
270     // Build a struct with the union sub-element as the first member,
271     // and padded to the appropriate size
272     std::vector<llvm::Constant*> Elts;
273     std::vector<const llvm::Type*> Types;
274     Elts.push_back(C);
275     Types.push_back(C->getType());
276     unsigned CurSize = CGM.getTargetData().getTypeStoreSize(C->getType());
277     unsigned TotalSize = CGM.getTargetData().getTypeStoreSize(Ty);
278     while (CurSize < TotalSize) {
279       Elts.push_back(llvm::Constant::getNullValue(llvm::Type::Int8Ty));
280       Types.push_back(llvm::Type::Int8Ty);
281       CurSize++;
282     }
283 
284     // This always generates a packed struct
285     // FIXME: Try to generate an unpacked struct when we can
286     llvm::StructType* STy = llvm::StructType::get(Types, true);
287     return llvm::ConstantStruct::get(STy, Elts);
288   }
289 
290   llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
291     const llvm::VectorType *VType =
292         cast<llvm::VectorType>(ConvertType(ILE->getType()));
293     const llvm::Type *ElemTy = VType->getElementType();
294     std::vector<llvm::Constant*> Elts;
295     unsigned NumElements = VType->getNumElements();
296     unsigned NumInitElements = ILE->getNumInits();
297 
298     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
299 
300     // Copy initializer elements.
301     unsigned i = 0;
302     for (; i < NumInitableElts; ++i) {
303       llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(i), CGF);
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 *VisitInitListExpr(InitListExpr *ILE) {
314     if (ILE->getType()->isScalarType()) {
315       // We have a scalar in braces. Just use the first element.
316       if (ILE->getNumInits() > 0)
317         return CGM.EmitConstantExpr(ILE->getInit(0), CGF);
318 
319       const llvm::Type* RetTy = CGM.getTypes().ConvertType(ILE->getType());
320       return llvm::Constant::getNullValue(RetTy);
321     }
322 
323     // FIXME: We don't codegen or sema designators yet.
324     if (ILE->hadDesignators()) {
325       CGM.ErrorUnsupported(ILE, "initializer list with designators");
326       return llvm::UndefValue::get(ConvertType(ILE->getType()));
327     }
328 
329     if (ILE->getType()->isArrayType())
330       return EmitArrayInitialization(ILE);
331 
332     if (ILE->getType()->isStructureType())
333       return EmitStructInitialization(ILE);
334 
335     if (ILE->getType()->isUnionType())
336       return EmitUnionInitialization(ILE);
337 
338     if (ILE->getType()->isVectorType())
339       return EmitVectorInitialization(ILE);
340 
341     assert(0 && "Unable to handle InitListExpr");
342     // Get rid of control reaches end of void function warning.
343     // Not reached.
344     return 0;
345   }
346 
347   llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
348     Expr* SExpr = ICExpr->getSubExpr();
349     QualType SType = SExpr->getType();
350     llvm::Constant *C; // the intermediate expression
351     QualType T;        // the type of the intermediate expression
352     if (SType->isArrayType()) {
353       // Arrays decay to a pointer to the first element
354       // VLAs would require special handling, but they can't occur here
355       C = EmitLValue(SExpr);
356       llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
357       llvm::Constant *Ops[] = {Idx0, Idx0};
358       C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
359       T = CGM.getContext().getArrayDecayedType(SType);
360     } else if (SType->isFunctionType()) {
361       // Function types decay to a pointer to the function
362       C = EmitLValue(SExpr);
363       T = CGM.getContext().getPointerType(SType);
364     } else {
365       C = Visit(SExpr);
366       T = SType;
367     }
368 
369     // Perform the conversion; note that an implicit cast can both promote
370     // and convert an array/function
371     return EmitConversion(C, T, ICExpr->getType());
372   }
373 
374   llvm::Constant *VisitStringLiteral(StringLiteral *E) {
375     assert(!E->getType()->isPointerType() && "Strings are always arrays");
376 
377     // Otherwise this must be a string initializing an array in a static
378     // initializer.  Don't emit it as the address of the string, emit the string
379     // data itself as an inline array.
380     return llvm::ConstantArray::get(CGM.GetStringForStringLiteral(E), false);
381   }
382 
383 #ifndef USE_TRY_EVALUATE
384   llvm::Constant *VisitDeclRefExpr(DeclRefExpr *E) {
385     const NamedDecl *Decl = E->getDecl();
386     if (const EnumConstantDecl *EC = dyn_cast<EnumConstantDecl>(Decl))
387       return llvm::ConstantInt::get(EC->getInitVal());
388     assert(0 && "Unsupported decl ref type!");
389     return 0;
390   }
391 
392   llvm::Constant *VisitSizeOfAlignOfExpr(const SizeOfAlignOfExpr *E) {
393     return EmitSizeAlignOf(E->getTypeOfArgument(), E->getType(), E->isSizeOf());
394   }
395 #endif
396 
397   llvm::Constant *VisitAddrLabelExpr(const AddrLabelExpr *E) {
398     assert(CGF && "Invalid address of label expression outside function.");
399     llvm::Constant *C =
400       llvm::ConstantInt::get(llvm::Type::Int32Ty,
401                              CGF->GetIDForAddrOfLabel(E->getLabel()));
402     return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
403   }
404 
405 #ifndef USE_TRY_EVALUATE
406   // Unary operators
407   llvm::Constant *VisitUnaryPlus(const UnaryOperator *E) {
408     return Visit(E->getSubExpr());
409   }
410   llvm::Constant *VisitUnaryMinus(const UnaryOperator *E) {
411     return llvm::ConstantExpr::getNeg(Visit(E->getSubExpr()));
412   }
413   llvm::Constant *VisitUnaryNot(const UnaryOperator *E) {
414     return llvm::ConstantExpr::getNot(Visit(E->getSubExpr()));
415   }
416   llvm::Constant *VisitUnaryLNot(const UnaryOperator *E) {
417     llvm::Constant *SubExpr = Visit(E->getSubExpr());
418 
419     if (E->getSubExpr()->getType()->isRealFloatingType()) {
420       // Compare against 0.0 for fp scalars.
421       llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
422       SubExpr = llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UEQ, SubExpr,
423                                             Zero);
424     } else {
425       assert((E->getSubExpr()->getType()->isIntegerType() ||
426               E->getSubExpr()->getType()->isPointerType()) &&
427              "Unknown scalar type to convert");
428       // Compare against an integer or pointer null.
429       llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
430       SubExpr = llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_EQ, SubExpr,
431                                             Zero);
432     }
433 
434     return llvm::ConstantExpr::getZExt(SubExpr, ConvertType(E->getType()));
435   }
436 #endif
437 
438   llvm::Constant *VisitUnaryAddrOf(const UnaryOperator *E) {
439     return EmitLValue(E->getSubExpr());
440   }
441   llvm::Constant *VisitUnaryOffsetOf(const UnaryOperator *E) {
442     int64_t Val = E->evaluateOffsetOf(CGM.getContext());
443 
444     assert(E->getType()->isIntegerType() && "Result type must be an integer!");
445 
446     uint32_t ResultWidth =
447       static_cast<uint32_t>(CGM.getContext().getTypeSize(E->getType()));
448     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
449   }
450 
451   llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
452     return Visit(E->getSubExpr());
453   }
454 
455   // Binary operators
456 #ifndef USE_TRY_EVALUATE
457   llvm::Constant *VisitBinOr(const BinaryOperator *E) {
458     llvm::Constant *LHS = Visit(E->getLHS());
459     llvm::Constant *RHS = Visit(E->getRHS());
460 
461     return llvm::ConstantExpr::getOr(LHS, RHS);
462   }
463   llvm::Constant *VisitBinSub(const BinaryOperator *E) {
464     llvm::Constant *LHS = Visit(E->getLHS());
465     llvm::Constant *RHS = Visit(E->getRHS());
466 
467     if (!isa<llvm::PointerType>(RHS->getType())) {
468       // pointer - int
469       if (isa<llvm::PointerType>(LHS->getType())) {
470         llvm::Constant *Idx = llvm::ConstantExpr::getNeg(RHS);
471 
472         return llvm::ConstantExpr::getGetElementPtr(LHS, &Idx, 1);
473       }
474 
475       // int - int
476       return llvm::ConstantExpr::getSub(LHS, RHS);
477     }
478 
479     assert(isa<llvm::PointerType>(LHS->getType()));
480 
481     const llvm::Type *ResultType = ConvertType(E->getType());
482     const QualType Type = E->getLHS()->getType();
483     const QualType ElementType = Type->getAsPointerType()->getPointeeType();
484 
485     LHS = llvm::ConstantExpr::getPtrToInt(LHS, ResultType);
486     RHS = llvm::ConstantExpr::getPtrToInt(RHS, ResultType);
487 
488     llvm::Constant *sub = llvm::ConstantExpr::getSub(LHS, RHS);
489     llvm::Constant *size = EmitSizeAlignOf(ElementType, E->getType(), true);
490     return llvm::ConstantExpr::getSDiv(sub, size);
491   }
492 
493   llvm::Constant *VisitBinShl(const BinaryOperator *E) {
494     llvm::Constant *LHS = Visit(E->getLHS());
495     llvm::Constant *RHS = Visit(E->getRHS());
496 
497     // LLVM requires the LHS and RHS to be the same type: promote or truncate the
498     // RHS to the same size as the LHS.
499     if (LHS->getType() != RHS->getType())
500       RHS = llvm::ConstantExpr::getIntegerCast(RHS, LHS->getType(), false);
501 
502     return llvm::ConstantExpr::getShl(LHS, RHS);
503   }
504 
505   llvm::Constant *VisitBinMul(const BinaryOperator *E) {
506     llvm::Constant *LHS = Visit(E->getLHS());
507     llvm::Constant *RHS = Visit(E->getRHS());
508 
509     return llvm::ConstantExpr::getMul(LHS, RHS);
510   }
511 
512   llvm::Constant *VisitBinDiv(const BinaryOperator *E) {
513     llvm::Constant *LHS = Visit(E->getLHS());
514     llvm::Constant *RHS = Visit(E->getRHS());
515 
516     if (LHS->getType()->isFPOrFPVector())
517       return llvm::ConstantExpr::getFDiv(LHS, RHS);
518     else if (E->getType()->isUnsignedIntegerType())
519       return llvm::ConstantExpr::getUDiv(LHS, RHS);
520     else
521       return llvm::ConstantExpr::getSDiv(LHS, RHS);
522   }
523 
524   llvm::Constant *VisitBinAdd(const BinaryOperator *E) {
525     llvm::Constant *LHS = Visit(E->getLHS());
526     llvm::Constant *RHS = Visit(E->getRHS());
527 
528     if (!E->getType()->isPointerType())
529       return llvm::ConstantExpr::getAdd(LHS, RHS);
530 
531     llvm::Constant *Ptr, *Idx;
532     if (isa<llvm::PointerType>(LHS->getType())) { // pointer + int
533       Ptr = LHS;
534       Idx = RHS;
535     } else { // int + pointer
536       Ptr = RHS;
537       Idx = LHS;
538     }
539 
540     return llvm::ConstantExpr::getGetElementPtr(Ptr, &Idx, 1);
541   }
542 
543   llvm::Constant *VisitBinAnd(const BinaryOperator *E) {
544     llvm::Constant *LHS = Visit(E->getLHS());
545     llvm::Constant *RHS = Visit(E->getRHS());
546 
547     return llvm::ConstantExpr::getAnd(LHS, RHS);
548   }
549 
550   llvm::Constant *EmitCmp(const BinaryOperator *E,
551                           llvm::CmpInst::Predicate SignedPred,
552                           llvm::CmpInst::Predicate UnsignedPred,
553                           llvm::CmpInst::Predicate FloatPred) {
554     llvm::Constant *LHS = Visit(E->getLHS());
555     llvm::Constant *RHS = Visit(E->getRHS());
556     llvm::Constant *Result;
557     if (LHS->getType()->isInteger() ||
558         isa<llvm::PointerType>(LHS->getType())) {
559       if (E->getLHS()->getType()->isSignedIntegerType())
560         Result = llvm::ConstantExpr::getICmp(SignedPred, LHS, RHS);
561       else
562         Result = llvm::ConstantExpr::getICmp(UnsignedPred, LHS, RHS);
563     } else if (LHS->getType()->isFloatingPoint()) {
564       Result = llvm::ConstantExpr::getFCmp(FloatPred, LHS, RHS);
565     } else {
566       CGM.ErrorUnsupported(E, "constant expression");
567       Result = llvm::ConstantInt::getFalse();
568     }
569 
570     const llvm::Type* ResultType = ConvertType(E->getType());
571     return llvm::ConstantExpr::getZExtOrBitCast(Result, ResultType);
572   }
573 
574   llvm::Constant *VisitBinNE(const BinaryOperator *E) {
575     return EmitCmp(E, llvm::CmpInst::ICMP_NE, llvm::CmpInst::ICMP_NE,
576                    llvm::CmpInst::FCMP_ONE);
577   }
578 
579   llvm::Constant *VisitBinEQ(const BinaryOperator *E) {
580     return EmitCmp(E, llvm::CmpInst::ICMP_EQ, llvm::CmpInst::ICMP_EQ,
581                    llvm::CmpInst::FCMP_OEQ);
582   }
583 
584   llvm::Constant *VisitBinLT(const BinaryOperator *E) {
585     return EmitCmp(E, llvm::CmpInst::ICMP_SLT, llvm::CmpInst::ICMP_ULT,
586                    llvm::CmpInst::FCMP_OLT);
587   }
588 
589   llvm::Constant *VisitBinLE(const BinaryOperator *E) {
590     return EmitCmp(E, llvm::CmpInst::ICMP_SLE, llvm::CmpInst::ICMP_ULE,
591                    llvm::CmpInst::FCMP_OLE);
592   }
593 
594   llvm::Constant *VisitBinGT(const BinaryOperator *E) {
595     return EmitCmp(E, llvm::CmpInst::ICMP_SGT, llvm::CmpInst::ICMP_UGT,
596                    llvm::CmpInst::FCMP_OGT);
597   }
598 
599   llvm::Constant *VisitBinGE(const BinaryOperator *E) {
600     return EmitCmp(E, llvm::CmpInst::ICMP_SGE, llvm::CmpInst::ICMP_SGE,
601                    llvm::CmpInst::FCMP_OGE);
602   }
603 
604   llvm::Constant *VisitConditionalOperator(const ConditionalOperator *E) {
605     llvm::Constant *Cond = Visit(E->getCond());
606     llvm::Constant *CondVal = EmitConversionToBool(Cond, E->getType());
607     llvm::ConstantInt *CondValInt = dyn_cast<llvm::ConstantInt>(CondVal);
608     if (!CondValInt) {
609       CGM.ErrorUnsupported(E, "constant expression");
610       return llvm::Constant::getNullValue(ConvertType(E->getType()));
611     }
612     if (CondValInt->isOne()) {
613       if (E->getLHS())
614         return Visit(E->getLHS());
615       return Cond;
616     }
617 
618     return Visit(E->getRHS());
619   }
620 #endif
621 
622   llvm::Constant *VisitCallExpr(const CallExpr *E) {
623     APValue Result;
624     if (E->Evaluate(Result, CGM.getContext())) {
625       if (Result.isInt())
626         return llvm::ConstantInt::get(Result.getInt());
627       if (Result.isFloat())
628         return llvm::ConstantFP::get(Result.getFloat());
629     }
630 
631     // Handle __builtin___CFStringMakeConstantString.
632     if (E->isBuiltinCall() ==Builtin::BI__builtin___CFStringMakeConstantString){
633       const Expr *Arg = E->getArg(0)->IgnoreParenCasts();
634 
635       const StringLiteral *Literal = cast<StringLiteral>(Arg);
636       std::string S(Literal->getStrData(), Literal->getByteLength());
637       return CGM.GetAddrOfConstantCFString(S);
638     }
639 
640     CGM.ErrorUnsupported(E, "constant call expression");
641     return llvm::Constant::getNullValue(ConvertType(E->getType()));
642   }
643 
644   // Utility methods
645   const llvm::Type *ConvertType(QualType T) {
646     return CGM.getTypes().ConvertType(T);
647   }
648 
649   llvm::Constant *EmitConversionToBool(llvm::Constant *Src, QualType SrcType) {
650     assert(SrcType->isCanonical() && "EmitConversion strips typedefs");
651 
652     if (SrcType->isRealFloatingType()) {
653       // Compare against 0.0 for fp scalars.
654       llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
655       return llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UNE, Src, Zero);
656     }
657 
658     assert((SrcType->isIntegerType() || SrcType->isPointerType()) &&
659            "Unknown scalar type to convert");
660 
661     // Compare against an integer or pointer null.
662     llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
663     return llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_NE, Src, Zero);
664   }
665 
666   llvm::Constant *EmitConversion(llvm::Constant *Src, QualType SrcType,
667                                  QualType DstType) {
668     SrcType = CGM.getContext().getCanonicalType(SrcType);
669     DstType = CGM.getContext().getCanonicalType(DstType);
670     if (SrcType == DstType) return Src;
671 
672     // Handle conversions to bool first, they are special: comparisons against 0.
673     if (DstType->isBooleanType())
674       return EmitConversionToBool(Src, SrcType);
675 
676     const llvm::Type *DstTy = ConvertType(DstType);
677 
678     // Ignore conversions like int -> uint.
679     if (Src->getType() == DstTy)
680       return Src;
681 
682     // Handle pointer conversions next: pointers can only be converted to/from
683     // other pointers and integers.
684     if (isa<llvm::PointerType>(DstTy)) {
685       // The source value may be an integer, or a pointer.
686       if (isa<llvm::PointerType>(Src->getType()))
687         return llvm::ConstantExpr::getBitCast(Src, DstTy);
688       assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
689       return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
690     }
691 
692     if (isa<llvm::PointerType>(Src->getType())) {
693       // Must be an ptr to int cast.
694       assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
695       return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
696     }
697 
698     // A scalar source can be splatted to a vector of the same element type
699     if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
700       assert((cast<llvm::VectorType>(DstTy)->getElementType()
701               == Src->getType()) &&
702              "Vector element type must match scalar type to splat.");
703       unsigned NumElements = DstType->getAsVectorType()->getNumElements();
704       llvm::SmallVector<llvm::Constant*, 16> Elements;
705       for (unsigned i = 0; i < NumElements; i++)
706         Elements.push_back(Src);
707 
708       return llvm::ConstantVector::get(&Elements[0], NumElements);
709     }
710 
711     if (isa<llvm::VectorType>(Src->getType()) ||
712         isa<llvm::VectorType>(DstTy)) {
713       return llvm::ConstantExpr::getBitCast(Src, DstTy);
714     }
715 
716     // Finally, we have the arithmetic types: real int/float.
717     if (isa<llvm::IntegerType>(Src->getType())) {
718       bool InputSigned = SrcType->isSignedIntegerType();
719       if (isa<llvm::IntegerType>(DstTy))
720         return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
721       else if (InputSigned)
722         return llvm::ConstantExpr::getSIToFP(Src, DstTy);
723       else
724         return llvm::ConstantExpr::getUIToFP(Src, DstTy);
725     }
726 
727     assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
728     if (isa<llvm::IntegerType>(DstTy)) {
729       if (DstType->isSignedIntegerType())
730         return llvm::ConstantExpr::getFPToSI(Src, DstTy);
731       else
732         return llvm::ConstantExpr::getFPToUI(Src, DstTy);
733     }
734 
735     assert(DstTy->isFloatingPoint() && "Unknown real conversion");
736     if (DstTy->getTypeID() < Src->getType()->getTypeID())
737       return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
738     else
739       return llvm::ConstantExpr::getFPExtend(Src, DstTy);
740   }
741 
742   llvm::Constant *EmitSizeAlignOf(QualType TypeToSize,
743                                   QualType RetType, bool isSizeOf) {
744     std::pair<uint64_t, unsigned> Info =
745       CGM.getContext().getTypeInfo(TypeToSize);
746 
747     uint64_t Val = isSizeOf ? Info.first : Info.second;
748     Val /= 8;  // Return size in bytes, not bits.
749 
750     assert(RetType->isIntegerType() && "Result type must be an integer!");
751 
752     uint32_t ResultWidth =
753       static_cast<uint32_t>(CGM.getContext().getTypeSize(RetType));
754     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
755   }
756 
757 public:
758   llvm::Constant *EmitLValue(Expr *E) {
759     switch (E->getStmtClass()) {
760     default: break;
761     case Expr::ParenExprClass:
762       // Elide parenthesis
763       return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
764     case Expr::CompoundLiteralExprClass: {
765       // Note that due to the nature of compound literals, this is guaranteed
766       // to be the only use of the variable, so we just generate it here.
767       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
768       llvm::Constant* C = Visit(CLE->getInitializer());
769       C = new llvm::GlobalVariable(C->getType(),E->getType().isConstQualified(),
770                                    llvm::GlobalValue::InternalLinkage,
771                                    C, ".compoundliteral", &CGM.getModule());
772       return C;
773     }
774     case Expr::DeclRefExprClass: {
775       NamedDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
776       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
777         return CGM.GetAddrOfFunction(FD);
778       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
779         if (VD->isFileVarDecl())
780           return CGM.GetAddrOfGlobalVar(VD);
781         else if (VD->isBlockVarDecl()) {
782           assert(CGF && "Can't access static local vars without CGF");
783           return CGF->GetAddrOfStaticLocalVar(VD);
784         }
785       }
786       break;
787     }
788     case Expr::MemberExprClass: {
789       MemberExpr* ME = cast<MemberExpr>(E);
790       llvm::Constant *Base;
791       if (ME->isArrow())
792         Base = Visit(ME->getBase());
793       else
794         Base = EmitLValue(ME->getBase());
795 
796       unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(ME->getMemberDecl());
797       llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
798       llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
799                                                    FieldNumber);
800       llvm::Value *Ops[] = {Zero, Idx};
801       return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
802     }
803     case Expr::ArraySubscriptExprClass: {
804       ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
805       llvm::Constant *Base = Visit(ASExpr->getBase());
806       llvm::Constant *Index = Visit(ASExpr->getIdx());
807       assert(!ASExpr->getBase()->getType()->isVectorType() &&
808              "Taking the address of a vector component is illegal!");
809       return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
810     }
811     case Expr::StringLiteralClass:
812       return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
813     case Expr::ObjCStringLiteralClass: {
814       ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
815       std::string S(SL->getString()->getStrData(),
816                     SL->getString()->getByteLength());
817       llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(S);
818       return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
819     }
820     case Expr::UnaryOperatorClass: {
821       UnaryOperator *Exp = cast<UnaryOperator>(E);
822       switch (Exp->getOpcode()) {
823       default: break;
824       case UnaryOperator::Extension:
825         // Extension is just a wrapper for expressions
826         return EmitLValue(Exp->getSubExpr());
827       case UnaryOperator::Real:
828       case UnaryOperator::Imag: {
829         // The address of __real or __imag is just a GEP off the address
830         // of the internal expression
831         llvm::Constant* C = EmitLValue(Exp->getSubExpr());
832         llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
833         llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
834                                        Exp->getOpcode() == UnaryOperator::Imag);
835         llvm::Value *Ops[] = {Zero, Idx};
836         return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
837       }
838       case UnaryOperator::Deref:
839         // The address of a deref is just the value of the expression
840         return Visit(Exp->getSubExpr());
841       }
842       break;
843     }
844     }
845     CGM.ErrorUnsupported(E, "constant l-value expression");
846     llvm::Type *Ty = llvm::PointerType::getUnqual(ConvertType(E->getType()));
847     return llvm::UndefValue::get(Ty);
848   }
849 };
850 
851 }  // end anonymous namespace.
852 
853 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
854                                                 CodeGenFunction *CGF) {
855   QualType type = Context.getCanonicalType(E->getType());
856 
857 #ifdef USE_TRY_EVALUATE
858   APValue V;
859   if (E->Evaluate(V, Context)) {
860     // FIXME: Assert that the value doesn't have any side effects.
861     switch (V.getKind()) {
862     default: assert(0 && "unhandled value kind!");
863     case APValue::LValue: {
864       llvm::Constant *Offset = llvm::ConstantInt::get(llvm::Type::Int64Ty,
865                                                       V.getLValueOffset());
866 
867       if (const Expr *LVBase = V.getLValueBase()) {
868         llvm::Constant *C =
869           ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
870 
871         const llvm::Type *Type =
872           llvm::PointerType::getUnqual(llvm::Type::Int8Ty);
873         const llvm::Type *DestType = getTypes().ConvertTypeForMem(E->getType());
874 
875         // FIXME: It's a little ugly that we need to cast to a pointer,
876         // apply the GEP and then cast back.
877         C = llvm::ConstantExpr::getBitCast(C, Type);
878         C = llvm::ConstantExpr::getGetElementPtr(C, &Offset, 1);
879 
880         return llvm::ConstantExpr::getBitCast(C, DestType);
881       }
882 
883       return llvm::ConstantExpr::getIntToPtr(Offset,
884                                              getTypes().ConvertType(type));
885     }
886     case APValue::Int: {
887       llvm::Constant *C = llvm::ConstantInt::get(V.getInt());
888 
889       if (C->getType() == llvm::Type::Int1Ty) {
890         const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
891         C = llvm::ConstantExpr::getZExt(C, BoolTy);
892       }
893       return C;
894     }
895     case APValue::Float:
896       return llvm::ConstantFP::get(V.getFloat());
897     case APValue::ComplexFloat: {
898       llvm::Constant *Complex[2];
899 
900       Complex[0] = llvm::ConstantFP::get(V.getComplexFloatReal());
901       Complex[1] = llvm::ConstantFP::get(V.getComplexFloatImag());
902 
903       return llvm::ConstantStruct::get(Complex, 2);
904     }
905     }
906   }
907 #else
908   if (type->isIntegerType()) {
909     llvm::APSInt Value(static_cast<uint32_t>(Context.getTypeSize(type)));
910     if (E->isIntegerConstantExpr(Value, Context)) {
911       return llvm::ConstantInt::get(Value);
912     }
913   }
914 #endif
915 
916   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
917   if (C->getType() == llvm::Type::Int1Ty) {
918     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
919     C = llvm::ConstantExpr::getZExt(C, BoolTy);
920   }
921   return C;
922 }
923