1 //===--- CGExprConstant.cpp - Emit LLVM Code from Constant Expressions ----===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This contains code to emit Constant Expr nodes as LLVM code.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "CodeGenFunction.h"
15 #include "CodeGenModule.h"
16 #include "clang/AST/AST.h"
17 #include "llvm/Constants.h"
18 #include "llvm/Function.h"
19 #include "llvm/GlobalVariable.h"
20 #include "llvm/Support/Compiler.h"
21 #include "llvm/Target/TargetData.h"
22 using namespace clang;
23 using namespace CodeGen;
24 
25 namespace  {
26 class VISIBILITY_HIDDEN ConstExprEmitter :
27   public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
28   CodeGenModule &CGM;
29   CodeGenFunction *CGF;
30 public:
31   ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
32     : CGM(cgm), CGF(cgf) {
33   }
34 
35   //===--------------------------------------------------------------------===//
36   //                            Visitor Methods
37   //===--------------------------------------------------------------------===//
38 
39   llvm::Constant *VisitStmt(Stmt *S) {
40     CGM.WarnUnsupported(S, "constant expression");
41     QualType T = cast<Expr>(S)->getType();
42     return llvm::UndefValue::get(CGM.getTypes().ConvertType(T));
43   }
44 
45   llvm::Constant *VisitParenExpr(ParenExpr *PE) {
46     return Visit(PE->getSubExpr());
47   }
48 
49   // Leaves
50   llvm::Constant *VisitIntegerLiteral(const IntegerLiteral *E) {
51     return llvm::ConstantInt::get(E->getValue());
52   }
53   llvm::Constant *VisitFloatingLiteral(const FloatingLiteral *E) {
54     return llvm::ConstantFP::get(E->getValue());
55   }
56   llvm::Constant *VisitCharacterLiteral(const CharacterLiteral *E) {
57     return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
58   }
59   llvm::Constant *VisitCXXBoolLiteralExpr(const CXXBoolLiteralExpr *E) {
60     return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
61   }
62   llvm::Constant *VisitObjCStringLiteral(const ObjCStringLiteral *E) {
63     return CGM.getObjCRuntime()->GenerateConstantString(
64         E->getString()->getStrData(), E->getString()->getByteLength());
65   }
66 
67   llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
68     return Visit(E->getInitializer());
69   }
70 
71   llvm::Constant *VisitCastExpr(const CastExpr* E) {
72     llvm::Constant *C = Visit(E->getSubExpr());
73 
74     return EmitConversion(C, E->getSubExpr()->getType(), E->getType());
75   }
76 
77   llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
78     return Visit(DAE->getExpr());
79   }
80 
81   llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
82     std::vector<llvm::Constant*> Elts;
83     const llvm::ArrayType *AType =
84         cast<llvm::ArrayType>(ConvertType(ILE->getType()));
85     unsigned NumInitElements = ILE->getNumInits();
86     // FIXME: Check for wide strings
87     if (NumInitElements > 0 && isa<StringLiteral>(ILE->getInit(0)) &&
88         ILE->getType()->getAsArrayType()->getElementType()->isCharType())
89       return Visit(ILE->getInit(0));
90     const llvm::Type *ElemTy = AType->getElementType();
91     unsigned NumElements = AType->getNumElements();
92 
93     // Initialising an array requires us to automatically
94     // initialise any elements that have not been initialised explicitly
95     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
96 
97     // Copy initializer elements.
98     unsigned i = 0;
99     bool RewriteType = false;
100     for (; i < NumInitableElts; ++i) {
101       llvm::Constant *C = Visit(ILE->getInit(i));
102       RewriteType |= (C->getType() != ElemTy);
103       Elts.push_back(C);
104     }
105 
106     // Initialize remaining array elements.
107     for (; i < NumElements; ++i)
108       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
109 
110     if (RewriteType) {
111       // FIXME: Try to avoid packing the array
112       std::vector<const llvm::Type*> Types;
113       for (unsigned i = 0; i < Elts.size(); ++i)
114         Types.push_back(Elts[i]->getType());
115       const llvm::StructType *SType = llvm::StructType::get(Types, true);
116       return llvm::ConstantStruct::get(SType, Elts);
117     }
118 
119     return llvm::ConstantArray::get(AType, Elts);
120   }
121 
122   void InsertBitfieldIntoStruct(std::vector<llvm::Constant*>& Elts,
123                                 FieldDecl* Field, Expr* E) {
124     // Calculate the value to insert
125     llvm::Constant *C = Visit(E);
126     llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
127     if (!CI) {
128       CGM.WarnUnsupported(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     unsigned size = CGM.getTypes().getTargetData().getTypeStoreSizeInBits(Ty);
136     unsigned fieldOffset = CGM.getTypes().getLLVMFieldNo(Field) * size;
137     CodeGenTypes::BitFieldInfo bitFieldInfo =
138         CGM.getTypes().getBitFieldInfo(Field);
139     fieldOffset += bitFieldInfo.Begin;
140 
141     // Find where to start the insertion
142     // FIXME: This is O(n^2) in the number of bit-fields!
143     // FIXME: This won't work if the struct isn't completely packed!
144     unsigned offset = 0, i = 0;
145     while (offset < (fieldOffset & -8))
146       offset += CGM.getTypes().getTargetData().getTypeStoreSizeInBits(Elts[i++]->getType());
147 
148     // Insert the bits into the struct
149     // FIXME: This algorthm is only correct on X86!
150     // FIXME: THis algorthm assumes bit-fields only have byte-size elements!
151     unsigned bitsToInsert = bitFieldInfo.Size;
152     unsigned curBits = std::min(8 - (fieldOffset & 7), bitsToInsert);
153     unsigned byte = V.getLoBits(curBits).getZExtValue() << (fieldOffset & 7);
154     do {
155       llvm::Constant* byteC = llvm::ConstantInt::get(llvm::Type::Int8Ty, byte);
156       Elts[i] = llvm::ConstantExpr::getOr(Elts[i], byteC);
157       ++i;
158       V = V.lshr(curBits);
159       bitsToInsert -= curBits;
160 
161       if (!bitsToInsert)
162         break;
163 
164       curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
165       byte = V.getLoBits(curBits).getZExtValue();
166     } while (true);
167   }
168 
169   llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
170     const llvm::StructType *SType =
171         cast<llvm::StructType>(ConvertType(ILE->getType()));
172     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
173     std::vector<llvm::Constant*> Elts;
174 
175     // Initialize the whole structure to zero.
176     for (unsigned i = 0; i < SType->getNumElements(); ++i) {
177       const llvm::Type *FieldTy = SType->getElementType(i);
178       Elts.push_back(llvm::Constant::getNullValue(FieldTy));
179     }
180 
181     // Copy initializer elements. Skip padding fields.
182     unsigned EltNo = 0;  // Element no in ILE
183     int FieldNo = 0; // Field no in RecordDecl
184     bool RewriteType = false;
185     while (EltNo < ILE->getNumInits() && FieldNo < RD->getNumMembers()) {
186       FieldDecl* curField = RD->getMember(FieldNo);
187       FieldNo++;
188       if (!curField->getIdentifier())
189         continue;
190 
191       if (curField->isBitField()) {
192         InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(EltNo));
193       } else {
194         unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(curField);
195         llvm::Constant* C = Visit(ILE->getInit(EltNo));
196         RewriteType |= (C->getType() != Elts[FieldNo]->getType());
197         Elts[FieldNo] = C;
198       }
199       EltNo++;
200     }
201 
202     if (RewriteType) {
203       // FIXME: Make this work for non-packed structs
204       assert(SType->isPacked() && "Cannot recreate unpacked structs");
205       std::vector<const llvm::Type*> Types;
206       for (unsigned i = 0; i < Elts.size(); ++i)
207         Types.push_back(Elts[i]->getType());
208       SType = llvm::StructType::get(Types, true);
209     }
210 
211     return llvm::ConstantStruct::get(SType, Elts);
212   }
213 
214   llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
215     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
216     const llvm::Type *Ty = ConvertType(ILE->getType());
217 
218     // Find the field decl we're initializing, if any
219     int FieldNo = 0; // Field no in RecordDecl
220     FieldDecl* curField = 0;
221     while (FieldNo < RD->getNumMembers()) {
222       curField = RD->getMember(FieldNo);
223       FieldNo++;
224       if (curField->getIdentifier())
225         break;
226     }
227 
228     if (!curField || !curField->getIdentifier() || ILE->getNumInits() == 0)
229       return llvm::Constant::getNullValue(Ty);
230 
231     if (curField->isBitField()) {
232       // Create a dummy struct for bit-field insertion
233       unsigned NumElts = CGM.getTargetData().getABITypeSize(Ty) / 8;
234       llvm::Constant* NV = llvm::Constant::getNullValue(llvm::Type::Int8Ty);
235       std::vector<llvm::Constant*> Elts(NumElts, NV);
236 
237       InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
238       const llvm::ArrayType *RetTy =
239           llvm::ArrayType::get(NV->getType(), NumElts);
240       return llvm::ConstantArray::get(RetTy, Elts);
241     }
242 
243     llvm::Constant *C = Visit(ILE->getInit(0));
244 
245     // Build a struct with the union sub-element as the first member,
246     // and padded to the appropriate size
247     std::vector<llvm::Constant*> Elts;
248     std::vector<const llvm::Type*> Types;
249     Elts.push_back(C);
250     Types.push_back(C->getType());
251     unsigned CurSize = CGM.getTargetData().getTypeStoreSize(C->getType());
252     unsigned TotalSize = CGM.getTargetData().getTypeStoreSize(Ty);
253     while (CurSize < TotalSize) {
254       Elts.push_back(llvm::Constant::getNullValue(llvm::Type::Int8Ty));
255       Types.push_back(llvm::Type::Int8Ty);
256       CurSize++;
257     }
258 
259     // This always generates a packed struct
260     // FIXME: Try to generate an unpacked struct when we can
261     llvm::StructType* STy = llvm::StructType::get(Types, true);
262     return llvm::ConstantStruct::get(STy, Elts);
263   }
264 
265   llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
266     const llvm::VectorType *VType =
267         cast<llvm::VectorType>(ConvertType(ILE->getType()));
268     const llvm::Type *ElemTy = VType->getElementType();
269     std::vector<llvm::Constant*> Elts;
270     unsigned NumElements = VType->getNumElements();
271     unsigned NumInitElements = ILE->getNumInits();
272 
273     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
274 
275     // Copy initializer elements.
276     unsigned i = 0;
277     for (; i < NumInitableElts; ++i) {
278       llvm::Constant *C = Visit(ILE->getInit(i));
279       Elts.push_back(C);
280     }
281 
282     for (; i < NumElements; ++i)
283       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
284 
285     return llvm::ConstantVector::get(VType, Elts);
286   }
287 
288   llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
289     if (ILE->getType()->isScalarType()) {
290       // We have a scalar in braces. Just use the first element.
291       if (ILE->getNumInits() > 0)
292         return Visit(ILE->getInit(0));
293 
294       const llvm::Type* RetTy = CGM.getTypes().ConvertType(ILE->getType());
295       return llvm::Constant::getNullValue(RetTy);
296     }
297 
298     if (ILE->getType()->isArrayType())
299       return EmitArrayInitialization(ILE);
300 
301     if (ILE->getType()->isStructureType())
302       return EmitStructInitialization(ILE);
303 
304     if (ILE->getType()->isUnionType())
305       return EmitUnionInitialization(ILE);
306 
307     if (ILE->getType()->isVectorType())
308       return EmitVectorInitialization(ILE);
309 
310     assert(0 && "Unable to handle InitListExpr");
311     // Get rid of control reaches end of void function warning.
312     // Not reached.
313     return 0;
314   }
315 
316   llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
317     Expr* SExpr = ICExpr->getSubExpr();
318     QualType SType = SExpr->getType();
319     llvm::Constant *C; // the intermediate expression
320     QualType T;        // the type of the intermediate expression
321     if (SType->isArrayType()) {
322       // Arrays decay to a pointer to the first element
323       // VLAs would require special handling, but they can't occur here
324       C = EmitLValue(SExpr);
325       llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
326       llvm::Constant *Ops[] = {Idx0, Idx0};
327       C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
328 
329       QualType ElemType = SType->getAsArrayType()->getElementType();
330       T = CGM.getContext().getPointerType(ElemType);
331     } else if (SType->isFunctionType()) {
332       // Function types decay to a pointer to the function
333       C = EmitLValue(SExpr);
334       T = CGM.getContext().getPointerType(SType);
335     } else {
336       C = Visit(SExpr);
337       T = SType;
338     }
339 
340     // Perform the conversion; note that an implicit cast can both promote
341     // and convert an array/function
342     return EmitConversion(C, T, ICExpr->getType());
343   }
344 
345   llvm::Constant *VisitStringLiteral(StringLiteral *E) {
346     const char *StrData = E->getStrData();
347     unsigned Len = E->getByteLength();
348     assert(!E->getType()->isPointerType() && "Strings are always arrays");
349 
350     // Otherwise this must be a string initializing an array in a static
351     // initializer.  Don't emit it as the address of the string, emit the string
352     // data itself as an inline array.
353     const ConstantArrayType *CAT = E->getType()->getAsConstantArrayType();
354     assert(CAT && "String isn't pointer or array!");
355 
356     std::string Str(StrData, StrData + Len);
357     // Null terminate the string before potentially truncating it.
358     // FIXME: What about wchar_t strings?
359     Str.push_back(0);
360 
361     uint64_t RealLen = CAT->getSize().getZExtValue();
362     // String or grow the initializer to the required size.
363     if (RealLen != Str.size())
364       Str.resize(RealLen);
365 
366     return llvm::ConstantArray::get(Str, false);
367   }
368 
369   llvm::Constant *VisitDeclRefExpr(DeclRefExpr *E) {
370     const ValueDecl *Decl = E->getDecl();
371     if (const EnumConstantDecl *EC = dyn_cast<EnumConstantDecl>(Decl))
372       return llvm::ConstantInt::get(EC->getInitVal());
373     assert(0 && "Unsupported decl ref type!");
374     return 0;
375   }
376 
377   llvm::Constant *VisitSizeOfAlignOfTypeExpr(const SizeOfAlignOfTypeExpr *E) {
378     return EmitSizeAlignOf(E->getArgumentType(), E->getType(), E->isSizeOf());
379   }
380 
381   // Unary operators
382   llvm::Constant *VisitUnaryPlus(const UnaryOperator *E) {
383     return Visit(E->getSubExpr());
384   }
385   llvm::Constant *VisitUnaryMinus(const UnaryOperator *E) {
386     return llvm::ConstantExpr::getNeg(Visit(E->getSubExpr()));
387   }
388   llvm::Constant *VisitUnaryNot(const UnaryOperator *E) {
389     return llvm::ConstantExpr::getNot(Visit(E->getSubExpr()));
390   }
391   llvm::Constant *VisitUnaryLNot(const UnaryOperator *E) {
392     llvm::Constant *SubExpr = Visit(E->getSubExpr());
393 
394     if (E->getSubExpr()->getType()->isRealFloatingType()) {
395       // Compare against 0.0 for fp scalars.
396       llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
397       SubExpr = llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UEQ, SubExpr,
398                                             Zero);
399     } else {
400       assert((E->getSubExpr()->getType()->isIntegerType() ||
401               E->getSubExpr()->getType()->isPointerType()) &&
402              "Unknown scalar type to convert");
403       // Compare against an integer or pointer null.
404       llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
405       SubExpr = llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_EQ, SubExpr,
406                                             Zero);
407     }
408 
409     return llvm::ConstantExpr::getZExt(SubExpr, ConvertType(E->getType()));
410   }
411   llvm::Constant *VisitUnarySizeOf(const UnaryOperator *E) {
412     return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), true);
413   }
414   llvm::Constant *VisitUnaryAlignOf(const UnaryOperator *E) {
415     return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), false);
416   }
417   llvm::Constant *VisitUnaryAddrOf(const UnaryOperator *E) {
418     return EmitLValue(E->getSubExpr());
419   }
420   llvm::Constant *VisitUnaryOffsetOf(const UnaryOperator *E) {
421     int64_t Val = E->evaluateOffsetOf(CGM.getContext());
422 
423     assert(E->getType()->isIntegerType() && "Result type must be an integer!");
424 
425     uint32_t ResultWidth =
426       static_cast<uint32_t>(CGM.getContext().getTypeSize(E->getType()));
427     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
428   }
429 
430   llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
431     return Visit(E->getSubExpr());
432   }
433 
434   // Binary operators
435   llvm::Constant *VisitBinOr(const BinaryOperator *E) {
436     llvm::Constant *LHS = Visit(E->getLHS());
437     llvm::Constant *RHS = Visit(E->getRHS());
438 
439     return llvm::ConstantExpr::getOr(LHS, RHS);
440   }
441   llvm::Constant *VisitBinSub(const BinaryOperator *E) {
442     llvm::Constant *LHS = Visit(E->getLHS());
443     llvm::Constant *RHS = Visit(E->getRHS());
444 
445     if (!isa<llvm::PointerType>(RHS->getType())) {
446       // pointer - int
447       if (isa<llvm::PointerType>(LHS->getType())) {
448         llvm::Constant *Idx = llvm::ConstantExpr::getNeg(RHS);
449 
450         return llvm::ConstantExpr::getGetElementPtr(LHS, &Idx, 1);
451       }
452 
453       // int - int
454       return llvm::ConstantExpr::getSub(LHS, RHS);
455     }
456 
457     assert(isa<llvm::PointerType>(LHS->getType()));
458 
459     const llvm::Type *ResultType = ConvertType(E->getType());
460     const QualType Type = E->getLHS()->getType();
461     const QualType ElementType = Type->getAsPointerType()->getPointeeType();
462 
463     LHS = llvm::ConstantExpr::getPtrToInt(LHS, ResultType);
464     RHS = llvm::ConstantExpr::getPtrToInt(RHS, ResultType);
465 
466     llvm::Constant *sub = llvm::ConstantExpr::getSub(LHS, RHS);
467     llvm::Constant *size = EmitSizeAlignOf(ElementType, E->getType(), true);
468     return llvm::ConstantExpr::getSDiv(sub, size);
469   }
470 
471   llvm::Constant *VisitBinShl(const BinaryOperator *E) {
472     llvm::Constant *LHS = Visit(E->getLHS());
473     llvm::Constant *RHS = Visit(E->getRHS());
474 
475     // LLVM requires the LHS and RHS to be the same type: promote or truncate the
476     // RHS to the same size as the LHS.
477     if (LHS->getType() != RHS->getType())
478       RHS = llvm::ConstantExpr::getIntegerCast(RHS, LHS->getType(), false);
479 
480     return llvm::ConstantExpr::getShl(LHS, RHS);
481   }
482 
483   llvm::Constant *VisitBinMul(const BinaryOperator *E) {
484     llvm::Constant *LHS = Visit(E->getLHS());
485     llvm::Constant *RHS = Visit(E->getRHS());
486 
487     return llvm::ConstantExpr::getMul(LHS, RHS);
488   }
489 
490   llvm::Constant *VisitBinDiv(const BinaryOperator *E) {
491     llvm::Constant *LHS = Visit(E->getLHS());
492     llvm::Constant *RHS = Visit(E->getRHS());
493 
494     if (LHS->getType()->isFPOrFPVector())
495       return llvm::ConstantExpr::getFDiv(LHS, RHS);
496     else if (E->getType()->isUnsignedIntegerType())
497       return llvm::ConstantExpr::getUDiv(LHS, RHS);
498     else
499       return llvm::ConstantExpr::getSDiv(LHS, RHS);
500   }
501 
502   llvm::Constant *VisitBinAdd(const BinaryOperator *E) {
503     llvm::Constant *LHS = Visit(E->getLHS());
504     llvm::Constant *RHS = Visit(E->getRHS());
505 
506     if (!E->getType()->isPointerType())
507       return llvm::ConstantExpr::getAdd(LHS, RHS);
508 
509     llvm::Constant *Ptr, *Idx;
510     if (isa<llvm::PointerType>(LHS->getType())) { // pointer + int
511       Ptr = LHS;
512       Idx = RHS;
513     } else { // int + pointer
514       Ptr = RHS;
515       Idx = LHS;
516     }
517 
518     return llvm::ConstantExpr::getGetElementPtr(Ptr, &Idx, 1);
519   }
520 
521   llvm::Constant *VisitBinAnd(const BinaryOperator *E) {
522     llvm::Constant *LHS = Visit(E->getLHS());
523     llvm::Constant *RHS = Visit(E->getRHS());
524 
525     return llvm::ConstantExpr::getAnd(LHS, RHS);
526   }
527 
528   llvm::Constant *EmitCmp(const BinaryOperator *E,
529                           llvm::CmpInst::Predicate SignedPred,
530                           llvm::CmpInst::Predicate UnsignedPred,
531                           llvm::CmpInst::Predicate FloatPred) {
532     llvm::Constant *LHS = Visit(E->getLHS());
533     llvm::Constant *RHS = Visit(E->getRHS());
534     llvm::Constant *Result;
535     if (LHS->getType()->isInteger() ||
536         isa<llvm::PointerType>(LHS->getType())) {
537       if (E->getLHS()->getType()->isSignedIntegerType())
538         Result = llvm::ConstantExpr::getICmp(SignedPred, LHS, RHS);
539       else
540         Result = llvm::ConstantExpr::getICmp(UnsignedPred, LHS, RHS);
541     } else if (LHS->getType()->isFloatingPoint()) {
542       Result = llvm::ConstantExpr::getFCmp(FloatPred, LHS, RHS);
543     } else {
544       CGM.WarnUnsupported(E, "constant expression");
545       Result = llvm::ConstantInt::getFalse();
546     }
547 
548     const llvm::Type* ResultType = ConvertType(E->getType());
549     return llvm::ConstantExpr::getZExtOrBitCast(Result, ResultType);
550   }
551 
552   llvm::Constant *VisitBinNE(const BinaryOperator *E) {
553     return EmitCmp(E, llvm::CmpInst::ICMP_NE, llvm::CmpInst::ICMP_NE,
554                    llvm::CmpInst::FCMP_ONE);
555   }
556 
557   llvm::Constant *VisitBinEQ(const BinaryOperator *E) {
558     return EmitCmp(E, llvm::CmpInst::ICMP_EQ, llvm::CmpInst::ICMP_EQ,
559                    llvm::CmpInst::FCMP_OEQ);
560   }
561 
562   llvm::Constant *VisitBinLT(const BinaryOperator *E) {
563     return EmitCmp(E, llvm::CmpInst::ICMP_SLT, llvm::CmpInst::ICMP_ULT,
564                    llvm::CmpInst::FCMP_OLT);
565   }
566 
567   llvm::Constant *VisitBinLE(const BinaryOperator *E) {
568     return EmitCmp(E, llvm::CmpInst::ICMP_SLE, llvm::CmpInst::ICMP_ULE,
569                    llvm::CmpInst::FCMP_OLE);
570   }
571 
572   llvm::Constant *VisitBinGT(const BinaryOperator *E) {
573     return EmitCmp(E, llvm::CmpInst::ICMP_SGT, llvm::CmpInst::ICMP_UGT,
574                    llvm::CmpInst::FCMP_OGT);
575   }
576 
577   llvm::Constant *VisitBinGE(const BinaryOperator *E) {
578     return EmitCmp(E, llvm::CmpInst::ICMP_SGE, llvm::CmpInst::ICMP_SGE,
579                    llvm::CmpInst::FCMP_OGE);
580   }
581 
582   llvm::Constant *VisitConditionalOperator(const ConditionalOperator *E) {
583     llvm::Constant *Cond = Visit(E->getCond());
584     llvm::Constant *CondVal = EmitConversionToBool(Cond, E->getType());
585     llvm::ConstantInt *CondValInt = dyn_cast<llvm::ConstantInt>(CondVal);
586     if (!CondValInt) {
587       CGM.WarnUnsupported(E, "constant expression");
588       return llvm::Constant::getNullValue(ConvertType(E->getType()));
589     }
590     if (CondValInt->isOne()) {
591       if (E->getLHS())
592         return Visit(E->getLHS());
593       return Cond;
594     }
595 
596     return Visit(E->getRHS());
597   }
598 
599   // Utility methods
600   const llvm::Type *ConvertType(QualType T) {
601     return CGM.getTypes().ConvertType(T);
602   }
603 
604   llvm::Constant *EmitConversionToBool(llvm::Constant *Src, QualType SrcType) {
605     assert(SrcType->isCanonical() && "EmitConversion strips typedefs");
606 
607     if (SrcType->isRealFloatingType()) {
608       // Compare against 0.0 for fp scalars.
609       llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
610       return llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UNE, Src, Zero);
611     }
612 
613     assert((SrcType->isIntegerType() || SrcType->isPointerType()) &&
614            "Unknown scalar type to convert");
615 
616     // Compare against an integer or pointer null.
617     llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
618     return llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_NE, Src, Zero);
619   }
620 
621   llvm::Constant *EmitConversion(llvm::Constant *Src, QualType SrcType,
622                                  QualType DstType) {
623     SrcType = SrcType.getCanonicalType();
624     DstType = DstType.getCanonicalType();
625     if (SrcType == DstType) return Src;
626 
627     // Handle conversions to bool first, they are special: comparisons against 0.
628     if (DstType->isBooleanType())
629       return EmitConversionToBool(Src, SrcType);
630 
631     const llvm::Type *DstTy = ConvertType(DstType);
632 
633     // Ignore conversions like int -> uint.
634     if (Src->getType() == DstTy)
635       return Src;
636 
637     // Handle pointer conversions next: pointers can only be converted to/from
638     // other pointers and integers.
639     if (isa<llvm::PointerType>(DstTy)) {
640       // The source value may be an integer, or a pointer.
641       if (isa<llvm::PointerType>(Src->getType()))
642         return llvm::ConstantExpr::getBitCast(Src, DstTy);
643       assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
644       return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
645     }
646 
647     if (isa<llvm::PointerType>(Src->getType())) {
648       // Must be an ptr to int cast.
649       assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
650       return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
651     }
652 
653     // A scalar source can be splatted to a vector of the same element type
654     if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
655       const llvm::VectorType *VT = cast<llvm::VectorType>(DstTy);
656       assert((VT->getElementType() == Src->getType()) &&
657              "Vector element type must match scalar type to splat.");
658       unsigned NumElements = DstType->getAsVectorType()->getNumElements();
659       llvm::SmallVector<llvm::Constant*, 16> Elements;
660       for (unsigned i = 0; i < NumElements; i++)
661         Elements.push_back(Src);
662 
663       return llvm::ConstantVector::get(&Elements[0], NumElements);
664     }
665 
666     if (isa<llvm::VectorType>(Src->getType()) ||
667         isa<llvm::VectorType>(DstTy)) {
668       return llvm::ConstantExpr::getBitCast(Src, DstTy);
669     }
670 
671     // Finally, we have the arithmetic types: real int/float.
672     if (isa<llvm::IntegerType>(Src->getType())) {
673       bool InputSigned = SrcType->isSignedIntegerType();
674       if (isa<llvm::IntegerType>(DstTy))
675         return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
676       else if (InputSigned)
677         return llvm::ConstantExpr::getSIToFP(Src, DstTy);
678       else
679         return llvm::ConstantExpr::getUIToFP(Src, DstTy);
680     }
681 
682     assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
683     if (isa<llvm::IntegerType>(DstTy)) {
684       if (DstType->isSignedIntegerType())
685         return llvm::ConstantExpr::getFPToSI(Src, DstTy);
686       else
687         return llvm::ConstantExpr::getFPToUI(Src, DstTy);
688     }
689 
690     assert(DstTy->isFloatingPoint() && "Unknown real conversion");
691     if (DstTy->getTypeID() < Src->getType()->getTypeID())
692       return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
693     else
694       return llvm::ConstantExpr::getFPExtend(Src, DstTy);
695   }
696 
697   llvm::Constant *EmitSizeAlignOf(QualType TypeToSize,
698                                   QualType RetType, bool isSizeOf) {
699     std::pair<uint64_t, unsigned> Info =
700       CGM.getContext().getTypeInfo(TypeToSize);
701 
702     uint64_t Val = isSizeOf ? Info.first : Info.second;
703     Val /= 8;  // Return size in bytes, not bits.
704 
705     assert(RetType->isIntegerType() && "Result type must be an integer!");
706 
707     uint32_t ResultWidth =
708       static_cast<uint32_t>(CGM.getContext().getTypeSize(RetType));
709     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
710   }
711 
712   llvm::Constant *EmitLValue(Expr *E) {
713     switch (E->getStmtClass()) {
714     default: break;
715     case Expr::ParenExprClass:
716       // Elide parenthesis
717       return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
718     case Expr::CompoundLiteralExprClass: {
719       // Note that due to the nature of compound literals, this is guaranteed
720       // to be the only use of the variable, so we just generate it here.
721       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
722       llvm::Constant* C = Visit(CLE->getInitializer());
723       C = new llvm::GlobalVariable(C->getType(),E->getType().isConstQualified(),
724                                    llvm::GlobalValue::InternalLinkage,
725                                    C, ".compoundliteral", &CGM.getModule());
726       return C;
727     }
728     case Expr::DeclRefExprClass: {
729       ValueDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
730       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
731         return CGM.GetAddrOfFunctionDecl(FD, false);
732       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
733         if (VD->isFileVarDecl())
734           return CGM.GetAddrOfGlobalVar(VD, false);
735         else if (VD->isBlockVarDecl()) {
736           assert(CGF && "Can't access static local vars without CGF");
737           return CGF->GetAddrOfStaticLocalVar(VD);
738         }
739       }
740       break;
741     }
742     case Expr::MemberExprClass: {
743       MemberExpr* ME = cast<MemberExpr>(E);
744       llvm::Constant *Base;
745       if (ME->isArrow())
746         Base = Visit(ME->getBase());
747       else
748         Base = EmitLValue(ME->getBase());
749 
750       unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(ME->getMemberDecl());
751       llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
752       llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
753                                                    FieldNumber);
754       llvm::Value *Ops[] = {Zero, Idx};
755       return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
756     }
757     case Expr::ArraySubscriptExprClass: {
758       ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
759       llvm::Constant *Base = Visit(ASExpr->getBase());
760       llvm::Constant *Index = Visit(ASExpr->getIdx());
761       assert(!ASExpr->getBase()->getType()->isVectorType() &&
762              "Taking the address of a vector component is illegal!");
763       return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
764     }
765     case Expr::StringLiteralClass: {
766       StringLiteral *String = cast<StringLiteral>(E);
767       assert(!String->isWide() && "Cannot codegen wide strings yet");
768       const char *StrData = String->getStrData();
769       unsigned Len = String->getByteLength();
770 
771       return CGM.GetAddrOfConstantString(std::string(StrData, StrData + Len));
772     }
773     case Expr::UnaryOperatorClass: {
774       UnaryOperator *Exp = cast<UnaryOperator>(E);
775       switch (Exp->getOpcode()) {
776       default: break;
777       case UnaryOperator::Extension:
778         // Extension is just a wrapper for expressions
779         return EmitLValue(Exp->getSubExpr());
780       case UnaryOperator::Real:
781       case UnaryOperator::Imag: {
782         // The address of __real or __imag is just a GEP off the address
783         // of the internal expression
784         llvm::Constant* C = EmitLValue(Exp->getSubExpr());
785         llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
786         llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
787                                        Exp->getOpcode() == UnaryOperator::Imag);
788         llvm::Value *Ops[] = {Zero, Idx};
789         return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
790       }
791       case UnaryOperator::Deref:
792         // The address of a deref is just the value of the expression
793         return Visit(Exp->getSubExpr());
794       }
795       break;
796     }
797     }
798     CGM.WarnUnsupported(E, "constant l-value expression");
799     llvm::Type *Ty = llvm::PointerType::getUnqual(ConvertType(E->getType()));
800     return llvm::UndefValue::get(Ty);
801   }
802 
803 };
804 
805 }  // end anonymous namespace.
806 
807 
808 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
809                                                 CodeGenFunction *CGF)
810 {
811   QualType type = E->getType().getCanonicalType();
812 
813   if (type->isIntegerType()) {
814     llvm::APSInt Value(static_cast<uint32_t>(Context.getTypeSize(type)));
815     if (E->isIntegerConstantExpr(Value, Context)) {
816       return llvm::ConstantInt::get(Value);
817     }
818   }
819 
820   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
821   if (C->getType() == llvm::Type::Int1Ty) {
822     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
823     C = llvm::ConstantExpr::getZExt(C, BoolTy);
824   }
825   return C;
826 }
827