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/ASTContext.h"
17 #include "clang/AST/StmtVisitor.h"
18 #include "llvm/Constants.h"
19 #include "llvm/Function.h"
20 #include "llvm/GlobalVariable.h"
21 #include "llvm/Support/Compiler.h"
22 #include "llvm/Target/TargetData.h"
23 using namespace clang;
24 using namespace CodeGen;
25 
26 namespace  {
27 class VISIBILITY_HIDDEN ConstExprEmitter :
28   public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
29   CodeGenModule &CGM;
30   CodeGenFunction *CGF;
31 public:
32   ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
33     : CGM(cgm), CGF(cgf) {
34   }
35 
36   //===--------------------------------------------------------------------===//
37   //                            Visitor Methods
38   //===--------------------------------------------------------------------===//
39 
40   llvm::Constant *VisitStmt(Stmt *S) {
41     CGM.WarnUnsupported(S, "constant expression");
42     QualType T = cast<Expr>(S)->getType();
43     return llvm::UndefValue::get(CGM.getTypes().ConvertType(T));
44   }
45 
46   llvm::Constant *VisitParenExpr(ParenExpr *PE) {
47     return Visit(PE->getSubExpr());
48   }
49 
50   // Leaves
51   llvm::Constant *VisitIntegerLiteral(const IntegerLiteral *E) {
52     return llvm::ConstantInt::get(E->getValue());
53   }
54   llvm::Constant *VisitFloatingLiteral(const FloatingLiteral *E) {
55     return llvm::ConstantFP::get(E->getValue());
56   }
57   llvm::Constant *VisitCharacterLiteral(const CharacterLiteral *E) {
58     return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
59   }
60   llvm::Constant *VisitCXXBoolLiteralExpr(const CXXBoolLiteralExpr *E) {
61     return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
62   }
63   llvm::Constant *VisitObjCStringLiteral(const ObjCStringLiteral *E) {
64     return CGM.getObjCRuntime().GenerateConstantString(
65         E->getString()->getStrData(), E->getString()->getByteLength());
66   }
67 
68   llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
69     return Visit(E->getInitializer());
70   }
71 
72   llvm::Constant *VisitCastExpr(const CastExpr* E) {
73     llvm::Constant *C = Visit(E->getSubExpr());
74 
75     return EmitConversion(C, E->getSubExpr()->getType(), E->getType());
76   }
77 
78   llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
79     return Visit(DAE->getExpr());
80   }
81 
82   llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
83     std::vector<llvm::Constant*> Elts;
84     const llvm::ArrayType *AType =
85         cast<llvm::ArrayType>(ConvertType(ILE->getType()));
86     unsigned NumInitElements = ILE->getNumInits();
87     // FIXME: Check for wide strings
88     if (NumInitElements > 0 && isa<StringLiteral>(ILE->getInit(0)) &&
89         ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
90       return Visit(ILE->getInit(0));
91     const llvm::Type *ElemTy = AType->getElementType();
92     unsigned NumElements = AType->getNumElements();
93 
94     // Initialising an array requires us to automatically
95     // initialise any elements that have not been initialised explicitly
96     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
97 
98     // Copy initializer elements.
99     unsigned i = 0;
100     bool RewriteType = false;
101     for (; i < NumInitableElts; ++i) {
102       llvm::Constant *C = Visit(ILE->getInit(i));
103       RewriteType |= (C->getType() != ElemTy);
104       Elts.push_back(C);
105     }
106 
107     // Initialize remaining array elements.
108     for (; i < NumElements; ++i)
109       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
110 
111     if (RewriteType) {
112       // FIXME: Try to avoid packing the array
113       std::vector<const llvm::Type*> Types;
114       for (unsigned i = 0; i < Elts.size(); ++i)
115         Types.push_back(Elts[i]->getType());
116       const llvm::StructType *SType = llvm::StructType::get(Types, true);
117       return llvm::ConstantStruct::get(SType, Elts);
118     }
119 
120     return llvm::ConstantArray::get(AType, Elts);
121   }
122 
123   void InsertBitfieldIntoStruct(std::vector<llvm::Constant*>& Elts,
124                                 FieldDecl* Field, Expr* E) {
125     // Calculate the value to insert
126     llvm::Constant *C = Visit(E);
127     llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
128     if (!CI) {
129       CGM.WarnUnsupported(E, "bitfield initialization");
130       return;
131     }
132     llvm::APInt V = CI->getValue();
133 
134     // Calculate information about the relevant field
135     const llvm::Type* Ty = CI->getType();
136     const llvm::TargetData &TD = CGM.getTypes().getTargetData();
137     unsigned size = TD.getTypeStoreSizeInBits(Ty);
138     unsigned fieldOffset = CGM.getTypes().getLLVMFieldNo(Field) * size;
139     CodeGenTypes::BitFieldInfo bitFieldInfo =
140         CGM.getTypes().getBitFieldInfo(Field);
141     fieldOffset += bitFieldInfo.Begin;
142 
143     // Find where to start the insertion
144     // FIXME: This is O(n^2) in the number of bit-fields!
145     // FIXME: This won't work if the struct isn't completely packed!
146     unsigned offset = 0, i = 0;
147     while (offset < (fieldOffset & -8))
148       offset += TD.getTypeStoreSizeInBits(Elts[i++]->getType());
149 
150     // Advance over 0 sized elements (must terminate in bounds since
151     // the bitfield must have a size).
152     while (TD.getTypeStoreSizeInBits(Elts[i]->getType()) == 0)
153       ++i;
154 
155     // Promote the size of V if necessary
156     // FIXME: This should never occur, but currently it can because
157     // initializer constants are cast to bool, and because clang is
158     // not enforcing bitfield width limits.
159     if (bitFieldInfo.Size > V.getBitWidth())
160       V.zext(bitFieldInfo.Size);
161 
162     // Insert the bits into the struct
163     // FIXME: This algorthm is only correct on X86!
164     // FIXME: THis algorthm assumes bit-fields only have byte-size elements!
165     unsigned bitsToInsert = bitFieldInfo.Size;
166     unsigned curBits = std::min(8 - (fieldOffset & 7), bitsToInsert);
167     unsigned byte = V.getLoBits(curBits).getZExtValue() << (fieldOffset & 7);
168     do {
169       llvm::Constant* byteC = llvm::ConstantInt::get(llvm::Type::Int8Ty, byte);
170       Elts[i] = llvm::ConstantExpr::getOr(Elts[i], byteC);
171       ++i;
172       V = V.lshr(curBits);
173       bitsToInsert -= curBits;
174 
175       if (!bitsToInsert)
176         break;
177 
178       curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
179       byte = V.getLoBits(curBits).getZExtValue();
180     } while (true);
181   }
182 
183   llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
184     const llvm::StructType *SType =
185         cast<llvm::StructType>(ConvertType(ILE->getType()));
186     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
187     std::vector<llvm::Constant*> Elts;
188 
189     // Initialize the whole structure to zero.
190     for (unsigned i = 0; i < SType->getNumElements(); ++i) {
191       const llvm::Type *FieldTy = SType->getElementType(i);
192       Elts.push_back(llvm::Constant::getNullValue(FieldTy));
193     }
194 
195     // Copy initializer elements. Skip padding fields.
196     unsigned EltNo = 0;  // Element no in ILE
197     int FieldNo = 0; // Field no in RecordDecl
198     bool RewriteType = false;
199     while (EltNo < ILE->getNumInits() && FieldNo < RD->getNumMembers()) {
200       FieldDecl* curField = RD->getMember(FieldNo);
201       FieldNo++;
202       if (!curField->getIdentifier())
203         continue;
204 
205       if (curField->isBitField()) {
206         InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(EltNo));
207       } else {
208         unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(curField);
209         llvm::Constant* C = Visit(ILE->getInit(EltNo));
210         RewriteType |= (C->getType() != Elts[FieldNo]->getType());
211         Elts[FieldNo] = C;
212       }
213       EltNo++;
214     }
215 
216     if (RewriteType) {
217       // FIXME: Make this work for non-packed structs
218       assert(SType->isPacked() && "Cannot recreate unpacked structs");
219       std::vector<const llvm::Type*> Types;
220       for (unsigned i = 0; i < Elts.size(); ++i)
221         Types.push_back(Elts[i]->getType());
222       SType = llvm::StructType::get(Types, true);
223     }
224 
225     return llvm::ConstantStruct::get(SType, Elts);
226   }
227 
228   llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
229     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
230     const llvm::Type *Ty = ConvertType(ILE->getType());
231 
232     // Find the field decl we're initializing, if any
233     int FieldNo = 0; // Field no in RecordDecl
234     FieldDecl* curField = 0;
235     while (FieldNo < RD->getNumMembers()) {
236       curField = RD->getMember(FieldNo);
237       FieldNo++;
238       if (curField->getIdentifier())
239         break;
240     }
241 
242     if (!curField || !curField->getIdentifier() || ILE->getNumInits() == 0)
243       return llvm::Constant::getNullValue(Ty);
244 
245     if (curField->isBitField()) {
246       // Create a dummy struct for bit-field insertion
247       unsigned NumElts = CGM.getTargetData().getABITypeSize(Ty) / 8;
248       llvm::Constant* NV = llvm::Constant::getNullValue(llvm::Type::Int8Ty);
249       std::vector<llvm::Constant*> Elts(NumElts, NV);
250 
251       InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
252       const llvm::ArrayType *RetTy =
253           llvm::ArrayType::get(NV->getType(), NumElts);
254       return llvm::ConstantArray::get(RetTy, Elts);
255     }
256 
257     llvm::Constant *C = Visit(ILE->getInit(0));
258 
259     // Build a struct with the union sub-element as the first member,
260     // and padded to the appropriate size
261     std::vector<llvm::Constant*> Elts;
262     std::vector<const llvm::Type*> Types;
263     Elts.push_back(C);
264     Types.push_back(C->getType());
265     unsigned CurSize = CGM.getTargetData().getTypeStoreSize(C->getType());
266     unsigned TotalSize = CGM.getTargetData().getTypeStoreSize(Ty);
267     while (CurSize < TotalSize) {
268       Elts.push_back(llvm::Constant::getNullValue(llvm::Type::Int8Ty));
269       Types.push_back(llvm::Type::Int8Ty);
270       CurSize++;
271     }
272 
273     // This always generates a packed struct
274     // FIXME: Try to generate an unpacked struct when we can
275     llvm::StructType* STy = llvm::StructType::get(Types, true);
276     return llvm::ConstantStruct::get(STy, Elts);
277   }
278 
279   llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
280     const llvm::VectorType *VType =
281         cast<llvm::VectorType>(ConvertType(ILE->getType()));
282     const llvm::Type *ElemTy = VType->getElementType();
283     std::vector<llvm::Constant*> Elts;
284     unsigned NumElements = VType->getNumElements();
285     unsigned NumInitElements = ILE->getNumInits();
286 
287     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
288 
289     // Copy initializer elements.
290     unsigned i = 0;
291     for (; i < NumInitableElts; ++i) {
292       llvm::Constant *C = Visit(ILE->getInit(i));
293       Elts.push_back(C);
294     }
295 
296     for (; i < NumElements; ++i)
297       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
298 
299     return llvm::ConstantVector::get(VType, Elts);
300   }
301 
302   llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
303     if (ILE->getType()->isScalarType()) {
304       // We have a scalar in braces. Just use the first element.
305       if (ILE->getNumInits() > 0)
306         return Visit(ILE->getInit(0));
307 
308       const llvm::Type* RetTy = CGM.getTypes().ConvertType(ILE->getType());
309       return llvm::Constant::getNullValue(RetTy);
310     }
311 
312     if (ILE->getType()->isArrayType())
313       return EmitArrayInitialization(ILE);
314 
315     if (ILE->getType()->isStructureType())
316       return EmitStructInitialization(ILE);
317 
318     if (ILE->getType()->isUnionType())
319       return EmitUnionInitialization(ILE);
320 
321     if (ILE->getType()->isVectorType())
322       return EmitVectorInitialization(ILE);
323 
324     assert(0 && "Unable to handle InitListExpr");
325     // Get rid of control reaches end of void function warning.
326     // Not reached.
327     return 0;
328   }
329 
330   llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
331     Expr* SExpr = ICExpr->getSubExpr();
332     QualType SType = SExpr->getType();
333     llvm::Constant *C; // the intermediate expression
334     QualType T;        // the type of the intermediate expression
335     if (SType->isArrayType()) {
336       // Arrays decay to a pointer to the first element
337       // VLAs would require special handling, but they can't occur here
338       C = EmitLValue(SExpr);
339       llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
340       llvm::Constant *Ops[] = {Idx0, Idx0};
341       C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
342       T = CGM.getContext().getArrayDecayedType(SType);
343     } else if (SType->isFunctionType()) {
344       // Function types decay to a pointer to the function
345       C = EmitLValue(SExpr);
346       T = CGM.getContext().getPointerType(SType);
347     } else {
348       C = Visit(SExpr);
349       T = SType;
350     }
351 
352     // Perform the conversion; note that an implicit cast can both promote
353     // and convert an array/function
354     return EmitConversion(C, T, ICExpr->getType());
355   }
356 
357   llvm::Constant *VisitStringLiteral(StringLiteral *E) {
358     assert(!E->getType()->isPointerType() && "Strings are always arrays");
359 
360     // Otherwise this must be a string initializing an array in a static
361     // initializer.  Don't emit it as the address of the string, emit the string
362     // data itself as an inline array.
363     return llvm::ConstantArray::get(CGM.getStringForStringLiteral(E), false);
364   }
365 
366   llvm::Constant *VisitDeclRefExpr(DeclRefExpr *E) {
367     const ValueDecl *Decl = E->getDecl();
368     if (const EnumConstantDecl *EC = dyn_cast<EnumConstantDecl>(Decl))
369       return llvm::ConstantInt::get(EC->getInitVal());
370     assert(0 && "Unsupported decl ref type!");
371     return 0;
372   }
373 
374   llvm::Constant *VisitSizeOfAlignOfTypeExpr(const SizeOfAlignOfTypeExpr *E) {
375     return EmitSizeAlignOf(E->getArgumentType(), E->getType(), E->isSizeOf());
376   }
377 
378   // Unary operators
379   llvm::Constant *VisitUnaryPlus(const UnaryOperator *E) {
380     return Visit(E->getSubExpr());
381   }
382   llvm::Constant *VisitUnaryMinus(const UnaryOperator *E) {
383     return llvm::ConstantExpr::getNeg(Visit(E->getSubExpr()));
384   }
385   llvm::Constant *VisitUnaryNot(const UnaryOperator *E) {
386     return llvm::ConstantExpr::getNot(Visit(E->getSubExpr()));
387   }
388   llvm::Constant *VisitUnaryLNot(const UnaryOperator *E) {
389     llvm::Constant *SubExpr = Visit(E->getSubExpr());
390 
391     if (E->getSubExpr()->getType()->isRealFloatingType()) {
392       // Compare against 0.0 for fp scalars.
393       llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
394       SubExpr = llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UEQ, SubExpr,
395                                             Zero);
396     } else {
397       assert((E->getSubExpr()->getType()->isIntegerType() ||
398               E->getSubExpr()->getType()->isPointerType()) &&
399              "Unknown scalar type to convert");
400       // Compare against an integer or pointer null.
401       llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
402       SubExpr = llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_EQ, SubExpr,
403                                             Zero);
404     }
405 
406     return llvm::ConstantExpr::getZExt(SubExpr, ConvertType(E->getType()));
407   }
408   llvm::Constant *VisitUnarySizeOf(const UnaryOperator *E) {
409     return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), true);
410   }
411   llvm::Constant *VisitUnaryAlignOf(const UnaryOperator *E) {
412     return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), false);
413   }
414   llvm::Constant *VisitUnaryAddrOf(const UnaryOperator *E) {
415     return EmitLValue(E->getSubExpr());
416   }
417   llvm::Constant *VisitUnaryOffsetOf(const UnaryOperator *E) {
418     int64_t Val = E->evaluateOffsetOf(CGM.getContext());
419 
420     assert(E->getType()->isIntegerType() && "Result type must be an integer!");
421 
422     uint32_t ResultWidth =
423       static_cast<uint32_t>(CGM.getContext().getTypeSize(E->getType()));
424     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
425   }
426 
427   llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
428     return Visit(E->getSubExpr());
429   }
430 
431   // Binary operators
432   llvm::Constant *VisitBinOr(const BinaryOperator *E) {
433     llvm::Constant *LHS = Visit(E->getLHS());
434     llvm::Constant *RHS = Visit(E->getRHS());
435 
436     return llvm::ConstantExpr::getOr(LHS, RHS);
437   }
438   llvm::Constant *VisitBinSub(const BinaryOperator *E) {
439     llvm::Constant *LHS = Visit(E->getLHS());
440     llvm::Constant *RHS = Visit(E->getRHS());
441 
442     if (!isa<llvm::PointerType>(RHS->getType())) {
443       // pointer - int
444       if (isa<llvm::PointerType>(LHS->getType())) {
445         llvm::Constant *Idx = llvm::ConstantExpr::getNeg(RHS);
446 
447         return llvm::ConstantExpr::getGetElementPtr(LHS, &Idx, 1);
448       }
449 
450       // int - int
451       return llvm::ConstantExpr::getSub(LHS, RHS);
452     }
453 
454     assert(isa<llvm::PointerType>(LHS->getType()));
455 
456     const llvm::Type *ResultType = ConvertType(E->getType());
457     const QualType Type = E->getLHS()->getType();
458     const QualType ElementType = Type->getAsPointerType()->getPointeeType();
459 
460     LHS = llvm::ConstantExpr::getPtrToInt(LHS, ResultType);
461     RHS = llvm::ConstantExpr::getPtrToInt(RHS, ResultType);
462 
463     llvm::Constant *sub = llvm::ConstantExpr::getSub(LHS, RHS);
464     llvm::Constant *size = EmitSizeAlignOf(ElementType, E->getType(), true);
465     return llvm::ConstantExpr::getSDiv(sub, size);
466   }
467 
468   llvm::Constant *VisitBinShl(const BinaryOperator *E) {
469     llvm::Constant *LHS = Visit(E->getLHS());
470     llvm::Constant *RHS = Visit(E->getRHS());
471 
472     // LLVM requires the LHS and RHS to be the same type: promote or truncate the
473     // RHS to the same size as the LHS.
474     if (LHS->getType() != RHS->getType())
475       RHS = llvm::ConstantExpr::getIntegerCast(RHS, LHS->getType(), false);
476 
477     return llvm::ConstantExpr::getShl(LHS, RHS);
478   }
479 
480   llvm::Constant *VisitBinMul(const BinaryOperator *E) {
481     llvm::Constant *LHS = Visit(E->getLHS());
482     llvm::Constant *RHS = Visit(E->getRHS());
483 
484     return llvm::ConstantExpr::getMul(LHS, RHS);
485   }
486 
487   llvm::Constant *VisitBinDiv(const BinaryOperator *E) {
488     llvm::Constant *LHS = Visit(E->getLHS());
489     llvm::Constant *RHS = Visit(E->getRHS());
490 
491     if (LHS->getType()->isFPOrFPVector())
492       return llvm::ConstantExpr::getFDiv(LHS, RHS);
493     else if (E->getType()->isUnsignedIntegerType())
494       return llvm::ConstantExpr::getUDiv(LHS, RHS);
495     else
496       return llvm::ConstantExpr::getSDiv(LHS, RHS);
497   }
498 
499   llvm::Constant *VisitBinAdd(const BinaryOperator *E) {
500     llvm::Constant *LHS = Visit(E->getLHS());
501     llvm::Constant *RHS = Visit(E->getRHS());
502 
503     if (!E->getType()->isPointerType())
504       return llvm::ConstantExpr::getAdd(LHS, RHS);
505 
506     llvm::Constant *Ptr, *Idx;
507     if (isa<llvm::PointerType>(LHS->getType())) { // pointer + int
508       Ptr = LHS;
509       Idx = RHS;
510     } else { // int + pointer
511       Ptr = RHS;
512       Idx = LHS;
513     }
514 
515     return llvm::ConstantExpr::getGetElementPtr(Ptr, &Idx, 1);
516   }
517 
518   llvm::Constant *VisitBinAnd(const BinaryOperator *E) {
519     llvm::Constant *LHS = Visit(E->getLHS());
520     llvm::Constant *RHS = Visit(E->getRHS());
521 
522     return llvm::ConstantExpr::getAnd(LHS, RHS);
523   }
524 
525   llvm::Constant *EmitCmp(const BinaryOperator *E,
526                           llvm::CmpInst::Predicate SignedPred,
527                           llvm::CmpInst::Predicate UnsignedPred,
528                           llvm::CmpInst::Predicate FloatPred) {
529     llvm::Constant *LHS = Visit(E->getLHS());
530     llvm::Constant *RHS = Visit(E->getRHS());
531     llvm::Constant *Result;
532     if (LHS->getType()->isInteger() ||
533         isa<llvm::PointerType>(LHS->getType())) {
534       if (E->getLHS()->getType()->isSignedIntegerType())
535         Result = llvm::ConstantExpr::getICmp(SignedPred, LHS, RHS);
536       else
537         Result = llvm::ConstantExpr::getICmp(UnsignedPred, LHS, RHS);
538     } else if (LHS->getType()->isFloatingPoint()) {
539       Result = llvm::ConstantExpr::getFCmp(FloatPred, LHS, RHS);
540     } else {
541       CGM.WarnUnsupported(E, "constant expression");
542       Result = llvm::ConstantInt::getFalse();
543     }
544 
545     const llvm::Type* ResultType = ConvertType(E->getType());
546     return llvm::ConstantExpr::getZExtOrBitCast(Result, ResultType);
547   }
548 
549   llvm::Constant *VisitBinNE(const BinaryOperator *E) {
550     return EmitCmp(E, llvm::CmpInst::ICMP_NE, llvm::CmpInst::ICMP_NE,
551                    llvm::CmpInst::FCMP_ONE);
552   }
553 
554   llvm::Constant *VisitBinEQ(const BinaryOperator *E) {
555     return EmitCmp(E, llvm::CmpInst::ICMP_EQ, llvm::CmpInst::ICMP_EQ,
556                    llvm::CmpInst::FCMP_OEQ);
557   }
558 
559   llvm::Constant *VisitBinLT(const BinaryOperator *E) {
560     return EmitCmp(E, llvm::CmpInst::ICMP_SLT, llvm::CmpInst::ICMP_ULT,
561                    llvm::CmpInst::FCMP_OLT);
562   }
563 
564   llvm::Constant *VisitBinLE(const BinaryOperator *E) {
565     return EmitCmp(E, llvm::CmpInst::ICMP_SLE, llvm::CmpInst::ICMP_ULE,
566                    llvm::CmpInst::FCMP_OLE);
567   }
568 
569   llvm::Constant *VisitBinGT(const BinaryOperator *E) {
570     return EmitCmp(E, llvm::CmpInst::ICMP_SGT, llvm::CmpInst::ICMP_UGT,
571                    llvm::CmpInst::FCMP_OGT);
572   }
573 
574   llvm::Constant *VisitBinGE(const BinaryOperator *E) {
575     return EmitCmp(E, llvm::CmpInst::ICMP_SGE, llvm::CmpInst::ICMP_SGE,
576                    llvm::CmpInst::FCMP_OGE);
577   }
578 
579   llvm::Constant *VisitConditionalOperator(const ConditionalOperator *E) {
580     llvm::Constant *Cond = Visit(E->getCond());
581     llvm::Constant *CondVal = EmitConversionToBool(Cond, E->getType());
582     llvm::ConstantInt *CondValInt = dyn_cast<llvm::ConstantInt>(CondVal);
583     if (!CondValInt) {
584       CGM.WarnUnsupported(E, "constant expression");
585       return llvm::Constant::getNullValue(ConvertType(E->getType()));
586     }
587     if (CondValInt->isOne()) {
588       if (E->getLHS())
589         return Visit(E->getLHS());
590       return Cond;
591     }
592 
593     return Visit(E->getRHS());
594   }
595 
596   // Utility methods
597   const llvm::Type *ConvertType(QualType T) {
598     return CGM.getTypes().ConvertType(T);
599   }
600 
601   llvm::Constant *EmitConversionToBool(llvm::Constant *Src, QualType SrcType) {
602     assert(SrcType->isCanonical() && "EmitConversion strips typedefs");
603 
604     if (SrcType->isRealFloatingType()) {
605       // Compare against 0.0 for fp scalars.
606       llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
607       return llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UNE, Src, Zero);
608     }
609 
610     assert((SrcType->isIntegerType() || SrcType->isPointerType()) &&
611            "Unknown scalar type to convert");
612 
613     // Compare against an integer or pointer null.
614     llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
615     return llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_NE, Src, Zero);
616   }
617 
618   llvm::Constant *EmitConversion(llvm::Constant *Src, QualType SrcType,
619                                  QualType DstType) {
620     SrcType = CGM.getContext().getCanonicalType(SrcType);
621     DstType = CGM.getContext().getCanonicalType(DstType);
622     if (SrcType == DstType) return Src;
623 
624     // Handle conversions to bool first, they are special: comparisons against 0.
625     if (DstType->isBooleanType())
626       return EmitConversionToBool(Src, SrcType);
627 
628     const llvm::Type *DstTy = ConvertType(DstType);
629 
630     // Ignore conversions like int -> uint.
631     if (Src->getType() == DstTy)
632       return Src;
633 
634     // Handle pointer conversions next: pointers can only be converted to/from
635     // other pointers and integers.
636     if (isa<llvm::PointerType>(DstTy)) {
637       // The source value may be an integer, or a pointer.
638       if (isa<llvm::PointerType>(Src->getType()))
639         return llvm::ConstantExpr::getBitCast(Src, DstTy);
640       assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
641       return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
642     }
643 
644     if (isa<llvm::PointerType>(Src->getType())) {
645       // Must be an ptr to int cast.
646       assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
647       return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
648     }
649 
650     // A scalar source can be splatted to a vector of the same element type
651     if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
652       const llvm::VectorType *VT = cast<llvm::VectorType>(DstTy);
653       assert((VT->getElementType() == Src->getType()) &&
654              "Vector element type must match scalar type to splat.");
655       unsigned NumElements = DstType->getAsVectorType()->getNumElements();
656       llvm::SmallVector<llvm::Constant*, 16> Elements;
657       for (unsigned i = 0; i < NumElements; i++)
658         Elements.push_back(Src);
659 
660       return llvm::ConstantVector::get(&Elements[0], NumElements);
661     }
662 
663     if (isa<llvm::VectorType>(Src->getType()) ||
664         isa<llvm::VectorType>(DstTy)) {
665       return llvm::ConstantExpr::getBitCast(Src, DstTy);
666     }
667 
668     // Finally, we have the arithmetic types: real int/float.
669     if (isa<llvm::IntegerType>(Src->getType())) {
670       bool InputSigned = SrcType->isSignedIntegerType();
671       if (isa<llvm::IntegerType>(DstTy))
672         return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
673       else if (InputSigned)
674         return llvm::ConstantExpr::getSIToFP(Src, DstTy);
675       else
676         return llvm::ConstantExpr::getUIToFP(Src, DstTy);
677     }
678 
679     assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
680     if (isa<llvm::IntegerType>(DstTy)) {
681       if (DstType->isSignedIntegerType())
682         return llvm::ConstantExpr::getFPToSI(Src, DstTy);
683       else
684         return llvm::ConstantExpr::getFPToUI(Src, DstTy);
685     }
686 
687     assert(DstTy->isFloatingPoint() && "Unknown real conversion");
688     if (DstTy->getTypeID() < Src->getType()->getTypeID())
689       return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
690     else
691       return llvm::ConstantExpr::getFPExtend(Src, DstTy);
692   }
693 
694   llvm::Constant *EmitSizeAlignOf(QualType TypeToSize,
695                                   QualType RetType, bool isSizeOf) {
696     std::pair<uint64_t, unsigned> Info =
697       CGM.getContext().getTypeInfo(TypeToSize);
698 
699     uint64_t Val = isSizeOf ? Info.first : Info.second;
700     Val /= 8;  // Return size in bytes, not bits.
701 
702     assert(RetType->isIntegerType() && "Result type must be an integer!");
703 
704     uint32_t ResultWidth =
705       static_cast<uint32_t>(CGM.getContext().getTypeSize(RetType));
706     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
707   }
708 
709   llvm::Constant *EmitLValue(Expr *E) {
710     switch (E->getStmtClass()) {
711     default: break;
712     case Expr::ParenExprClass:
713       // Elide parenthesis
714       return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
715     case Expr::CompoundLiteralExprClass: {
716       // Note that due to the nature of compound literals, this is guaranteed
717       // to be the only use of the variable, so we just generate it here.
718       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
719       llvm::Constant* C = Visit(CLE->getInitializer());
720       C = new llvm::GlobalVariable(C->getType(),E->getType().isConstQualified(),
721                                    llvm::GlobalValue::InternalLinkage,
722                                    C, ".compoundliteral", &CGM.getModule());
723       return C;
724     }
725     case Expr::DeclRefExprClass: {
726       ValueDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
727       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
728         return CGM.GetAddrOfFunction(FD);
729       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
730         if (VD->isFileVarDecl())
731           return CGM.GetAddrOfGlobalVar(VD);
732         else if (VD->isBlockVarDecl()) {
733           assert(CGF && "Can't access static local vars without CGF");
734           return CGF->GetAddrOfStaticLocalVar(VD);
735         }
736       }
737       break;
738     }
739     case Expr::MemberExprClass: {
740       MemberExpr* ME = cast<MemberExpr>(E);
741       llvm::Constant *Base;
742       if (ME->isArrow())
743         Base = Visit(ME->getBase());
744       else
745         Base = EmitLValue(ME->getBase());
746 
747       unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(ME->getMemberDecl());
748       llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
749       llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
750                                                    FieldNumber);
751       llvm::Value *Ops[] = {Zero, Idx};
752       return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
753     }
754     case Expr::ArraySubscriptExprClass: {
755       ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
756       llvm::Constant *Base = Visit(ASExpr->getBase());
757       llvm::Constant *Index = Visit(ASExpr->getIdx());
758       assert(!ASExpr->getBase()->getType()->isVectorType() &&
759              "Taking the address of a vector component is illegal!");
760       return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
761     }
762     case Expr::StringLiteralClass: {
763       StringLiteral *S = cast<StringLiteral>(E);
764       return CGM.GetAddrOfConstantString(CGM.getStringForStringLiteral(S));
765     }
766     case Expr::UnaryOperatorClass: {
767       UnaryOperator *Exp = cast<UnaryOperator>(E);
768       switch (Exp->getOpcode()) {
769       default: break;
770       case UnaryOperator::Extension:
771         // Extension is just a wrapper for expressions
772         return EmitLValue(Exp->getSubExpr());
773       case UnaryOperator::Real:
774       case UnaryOperator::Imag: {
775         // The address of __real or __imag is just a GEP off the address
776         // of the internal expression
777         llvm::Constant* C = EmitLValue(Exp->getSubExpr());
778         llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
779         llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
780                                        Exp->getOpcode() == UnaryOperator::Imag);
781         llvm::Value *Ops[] = {Zero, Idx};
782         return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
783       }
784       case UnaryOperator::Deref:
785         // The address of a deref is just the value of the expression
786         return Visit(Exp->getSubExpr());
787       }
788       break;
789     }
790     }
791     CGM.WarnUnsupported(E, "constant l-value expression");
792     llvm::Type *Ty = llvm::PointerType::getUnqual(ConvertType(E->getType()));
793     return llvm::UndefValue::get(Ty);
794   }
795 
796 };
797 
798 }  // end anonymous namespace.
799 
800 
801 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
802                                                 CodeGenFunction *CGF) {
803   QualType type = Context.getCanonicalType(E->getType());
804 
805   if (type->isIntegerType()) {
806     llvm::APSInt Value(static_cast<uint32_t>(Context.getTypeSize(type)));
807     if (E->isIntegerConstantExpr(Value, Context)) {
808       return llvm::ConstantInt::get(Value);
809     }
810   }
811 
812   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
813   if (C->getType() == llvm::Type::Int1Ty) {
814     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
815     C = llvm::ConstantExpr::getZExt(C, BoolTy);
816   }
817   return C;
818 }
819