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/ASTContext.h"
18 #include "clang/AST/StmtVisitor.h"
19 #include "llvm/Constants.h"
20 #include "llvm/Function.h"
21 #include "llvm/GlobalVariable.h"
22 #include "llvm/Support/Compiler.h"
23 #include "llvm/Target/TargetData.h"
24 using namespace clang;
25 using namespace CodeGen;
26 
27 namespace  {
28 class VISIBILITY_HIDDEN ConstExprEmitter :
29   public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
30   CodeGenModule &CGM;
31   CodeGenFunction *CGF;
32 public:
33   ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
34     : CGM(cgm), CGF(cgf) {
35   }
36 
37   //===--------------------------------------------------------------------===//
38   //                            Visitor Methods
39   //===--------------------------------------------------------------------===//
40 
41   llvm::Constant *VisitStmt(Stmt *S) {
42     CGM.WarnUnsupported(S, "constant expression");
43     QualType T = cast<Expr>(S)->getType();
44     return llvm::UndefValue::get(CGM.getTypes().ConvertType(T));
45   }
46 
47   llvm::Constant *VisitParenExpr(ParenExpr *PE) {
48     return Visit(PE->getSubExpr());
49   }
50 
51   // Leaves
52   llvm::Constant *VisitIntegerLiteral(const IntegerLiteral *E) {
53     return llvm::ConstantInt::get(E->getValue());
54   }
55   llvm::Constant *VisitFloatingLiteral(const FloatingLiteral *E) {
56     return llvm::ConstantFP::get(E->getValue());
57   }
58   llvm::Constant *VisitCharacterLiteral(const CharacterLiteral *E) {
59     return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
60   }
61   llvm::Constant *VisitCXXBoolLiteralExpr(const CXXBoolLiteralExpr *E) {
62     return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
63   }
64   llvm::Constant *VisitObjCStringLiteral(const ObjCStringLiteral *E) {
65     std::string S(E->getString()->getStrData(),
66                   E->getString()->getByteLength());
67     llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(S);
68     return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
69   }
70 
71   llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
72     return Visit(E->getInitializer());
73   }
74 
75   llvm::Constant *VisitCastExpr(const CastExpr* E) {
76     llvm::Constant *C = Visit(E->getSubExpr());
77 
78     return EmitConversion(C, E->getSubExpr()->getType(), E->getType());
79   }
80 
81   llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
82     return Visit(DAE->getExpr());
83   }
84 
85   llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
86     std::vector<llvm::Constant*> Elts;
87     const llvm::ArrayType *AType =
88         cast<llvm::ArrayType>(ConvertType(ILE->getType()));
89     unsigned NumInitElements = ILE->getNumInits();
90     // FIXME: Check for wide strings
91     if (NumInitElements > 0 && isa<StringLiteral>(ILE->getInit(0)) &&
92         ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
93       return Visit(ILE->getInit(0));
94     const llvm::Type *ElemTy = AType->getElementType();
95     unsigned NumElements = AType->getNumElements();
96 
97     // Initialising an array requires us to automatically
98     // initialise any elements that have not been initialised explicitly
99     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
100 
101     // Copy initializer elements.
102     unsigned i = 0;
103     bool RewriteType = false;
104     for (; i < NumInitableElts; ++i) {
105       llvm::Constant *C = Visit(ILE->getInit(i));
106       RewriteType |= (C->getType() != ElemTy);
107       Elts.push_back(C);
108     }
109 
110     // Initialize remaining array elements.
111     for (; i < NumElements; ++i)
112       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
113 
114     if (RewriteType) {
115       // FIXME: Try to avoid packing the array
116       std::vector<const llvm::Type*> Types;
117       for (unsigned i = 0; i < Elts.size(); ++i)
118         Types.push_back(Elts[i]->getType());
119       const llvm::StructType *SType = llvm::StructType::get(Types, true);
120       return llvm::ConstantStruct::get(SType, Elts);
121     }
122 
123     return llvm::ConstantArray::get(AType, Elts);
124   }
125 
126   void InsertBitfieldIntoStruct(std::vector<llvm::Constant*>& Elts,
127                                 FieldDecl* Field, Expr* E) {
128     // Calculate the value to insert
129     llvm::Constant *C = Visit(E);
130     llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
131     if (!CI) {
132       CGM.WarnUnsupported(E, "bitfield initialization");
133       return;
134     }
135     llvm::APInt V = CI->getValue();
136 
137     // Calculate information about the relevant field
138     const llvm::Type* Ty = CI->getType();
139     const llvm::TargetData &TD = CGM.getTypes().getTargetData();
140     unsigned size = TD.getTypeStoreSizeInBits(Ty);
141     unsigned fieldOffset = CGM.getTypes().getLLVMFieldNo(Field) * size;
142     CodeGenTypes::BitFieldInfo bitFieldInfo =
143         CGM.getTypes().getBitFieldInfo(Field);
144     fieldOffset += bitFieldInfo.Begin;
145 
146     // Find where to start the insertion
147     // FIXME: This is O(n^2) in the number of bit-fields!
148     // FIXME: This won't work if the struct isn't completely packed!
149     unsigned offset = 0, i = 0;
150     while (offset < (fieldOffset & -8))
151       offset += TD.getTypeStoreSizeInBits(Elts[i++]->getType());
152 
153     // Advance over 0 sized elements (must terminate in bounds since
154     // the bitfield must have a size).
155     while (TD.getTypeStoreSizeInBits(Elts[i]->getType()) == 0)
156       ++i;
157 
158     // Promote the size of V if necessary
159     // FIXME: This should never occur, but currently it can because
160     // initializer constants are cast to bool, and because clang is
161     // not enforcing bitfield width limits.
162     if (bitFieldInfo.Size > V.getBitWidth())
163       V.zext(bitFieldInfo.Size);
164 
165     // Insert the bits into the struct
166     // FIXME: This algorthm is only correct on X86!
167     // FIXME: THis algorthm assumes bit-fields only have byte-size elements!
168     unsigned bitsToInsert = bitFieldInfo.Size;
169     unsigned curBits = std::min(8 - (fieldOffset & 7), bitsToInsert);
170     unsigned byte = V.getLoBits(curBits).getZExtValue() << (fieldOffset & 7);
171     do {
172       llvm::Constant* byteC = llvm::ConstantInt::get(llvm::Type::Int8Ty, byte);
173       Elts[i] = llvm::ConstantExpr::getOr(Elts[i], byteC);
174       ++i;
175       V = V.lshr(curBits);
176       bitsToInsert -= curBits;
177 
178       if (!bitsToInsert)
179         break;
180 
181       curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
182       byte = V.getLoBits(curBits).getZExtValue();
183     } while (true);
184   }
185 
186   llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
187     const llvm::StructType *SType =
188         cast<llvm::StructType>(ConvertType(ILE->getType()));
189     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
190     std::vector<llvm::Constant*> Elts;
191 
192     // Initialize the whole structure to zero.
193     for (unsigned i = 0; i < SType->getNumElements(); ++i) {
194       const llvm::Type *FieldTy = SType->getElementType(i);
195       Elts.push_back(llvm::Constant::getNullValue(FieldTy));
196     }
197 
198     // Copy initializer elements. Skip padding fields.
199     unsigned EltNo = 0;  // Element no in ILE
200     int FieldNo = 0; // Field no in RecordDecl
201     bool RewriteType = false;
202     while (EltNo < ILE->getNumInits() && FieldNo < RD->getNumMembers()) {
203       FieldDecl* curField = RD->getMember(FieldNo);
204       FieldNo++;
205       if (!curField->getIdentifier())
206         continue;
207 
208       if (curField->isBitField()) {
209         InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(EltNo));
210       } else {
211         unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(curField);
212         llvm::Constant* C = Visit(ILE->getInit(EltNo));
213         RewriteType |= (C->getType() != Elts[FieldNo]->getType());
214         Elts[FieldNo] = C;
215       }
216       EltNo++;
217     }
218 
219     if (RewriteType) {
220       // FIXME: Make this work for non-packed structs
221       assert(SType->isPacked() && "Cannot recreate unpacked structs");
222       std::vector<const llvm::Type*> Types;
223       for (unsigned i = 0; i < Elts.size(); ++i)
224         Types.push_back(Elts[i]->getType());
225       SType = llvm::StructType::get(Types, true);
226     }
227 
228     return llvm::ConstantStruct::get(SType, Elts);
229   }
230 
231   llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
232     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
233     const llvm::Type *Ty = ConvertType(ILE->getType());
234 
235     // Find the field decl we're initializing, if any
236     int FieldNo = 0; // Field no in RecordDecl
237     FieldDecl* curField = 0;
238     while (FieldNo < RD->getNumMembers()) {
239       curField = RD->getMember(FieldNo);
240       FieldNo++;
241       if (curField->getIdentifier())
242         break;
243     }
244 
245     if (!curField || !curField->getIdentifier() || ILE->getNumInits() == 0)
246       return llvm::Constant::getNullValue(Ty);
247 
248     if (curField->isBitField()) {
249       // Create a dummy struct for bit-field insertion
250       unsigned NumElts = CGM.getTargetData().getABITypeSize(Ty) / 8;
251       llvm::Constant* NV = llvm::Constant::getNullValue(llvm::Type::Int8Ty);
252       std::vector<llvm::Constant*> Elts(NumElts, NV);
253 
254       InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
255       const llvm::ArrayType *RetTy =
256           llvm::ArrayType::get(NV->getType(), NumElts);
257       return llvm::ConstantArray::get(RetTy, Elts);
258     }
259 
260     llvm::Constant *C = Visit(ILE->getInit(0));
261 
262     // Build a struct with the union sub-element as the first member,
263     // and padded to the appropriate size
264     std::vector<llvm::Constant*> Elts;
265     std::vector<const llvm::Type*> Types;
266     Elts.push_back(C);
267     Types.push_back(C->getType());
268     unsigned CurSize = CGM.getTargetData().getTypeStoreSize(C->getType());
269     unsigned TotalSize = CGM.getTargetData().getTypeStoreSize(Ty);
270     while (CurSize < TotalSize) {
271       Elts.push_back(llvm::Constant::getNullValue(llvm::Type::Int8Ty));
272       Types.push_back(llvm::Type::Int8Ty);
273       CurSize++;
274     }
275 
276     // This always generates a packed struct
277     // FIXME: Try to generate an unpacked struct when we can
278     llvm::StructType* STy = llvm::StructType::get(Types, true);
279     return llvm::ConstantStruct::get(STy, Elts);
280   }
281 
282   llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
283     const llvm::VectorType *VType =
284         cast<llvm::VectorType>(ConvertType(ILE->getType()));
285     const llvm::Type *ElemTy = VType->getElementType();
286     std::vector<llvm::Constant*> Elts;
287     unsigned NumElements = VType->getNumElements();
288     unsigned NumInitElements = ILE->getNumInits();
289 
290     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
291 
292     // Copy initializer elements.
293     unsigned i = 0;
294     for (; i < NumInitableElts; ++i) {
295       llvm::Constant *C = Visit(ILE->getInit(i));
296       Elts.push_back(C);
297     }
298 
299     for (; i < NumElements; ++i)
300       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
301 
302     return llvm::ConstantVector::get(VType, Elts);
303   }
304 
305   llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
306     if (ILE->getType()->isScalarType()) {
307       // We have a scalar in braces. Just use the first element.
308       if (ILE->getNumInits() > 0)
309         return Visit(ILE->getInit(0));
310 
311       const llvm::Type* RetTy = CGM.getTypes().ConvertType(ILE->getType());
312       return llvm::Constant::getNullValue(RetTy);
313     }
314 
315     if (ILE->getType()->isArrayType())
316       return EmitArrayInitialization(ILE);
317 
318     if (ILE->getType()->isStructureType())
319       return EmitStructInitialization(ILE);
320 
321     if (ILE->getType()->isUnionType())
322       return EmitUnionInitialization(ILE);
323 
324     if (ILE->getType()->isVectorType())
325       return EmitVectorInitialization(ILE);
326 
327     assert(0 && "Unable to handle InitListExpr");
328     // Get rid of control reaches end of void function warning.
329     // Not reached.
330     return 0;
331   }
332 
333   llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
334     Expr* SExpr = ICExpr->getSubExpr();
335     QualType SType = SExpr->getType();
336     llvm::Constant *C; // the intermediate expression
337     QualType T;        // the type of the intermediate expression
338     if (SType->isArrayType()) {
339       // Arrays decay to a pointer to the first element
340       // VLAs would require special handling, but they can't occur here
341       C = EmitLValue(SExpr);
342       llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
343       llvm::Constant *Ops[] = {Idx0, Idx0};
344       C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
345       T = CGM.getContext().getArrayDecayedType(SType);
346     } else if (SType->isFunctionType()) {
347       // Function types decay to a pointer to the function
348       C = EmitLValue(SExpr);
349       T = CGM.getContext().getPointerType(SType);
350     } else {
351       C = Visit(SExpr);
352       T = SType;
353     }
354 
355     // Perform the conversion; note that an implicit cast can both promote
356     // and convert an array/function
357     return EmitConversion(C, T, ICExpr->getType());
358   }
359 
360   llvm::Constant *VisitStringLiteral(StringLiteral *E) {
361     assert(!E->getType()->isPointerType() && "Strings are always arrays");
362 
363     // Otherwise this must be a string initializing an array in a static
364     // initializer.  Don't emit it as the address of the string, emit the string
365     // data itself as an inline array.
366     return llvm::ConstantArray::get(CGM.GetStringForStringLiteral(E), 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 = CGM.getContext().getCanonicalType(SrcType);
624     DstType = CGM.getContext().getCanonicalType(DstType);
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.GetAddrOfFunction(FD);
732       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
733         if (VD->isFileVarDecl())
734           return CGM.GetAddrOfGlobalVar(VD);
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       return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
767     case Expr::UnaryOperatorClass: {
768       UnaryOperator *Exp = cast<UnaryOperator>(E);
769       switch (Exp->getOpcode()) {
770       default: break;
771       case UnaryOperator::Extension:
772         // Extension is just a wrapper for expressions
773         return EmitLValue(Exp->getSubExpr());
774       case UnaryOperator::Real:
775       case UnaryOperator::Imag: {
776         // The address of __real or __imag is just a GEP off the address
777         // of the internal expression
778         llvm::Constant* C = EmitLValue(Exp->getSubExpr());
779         llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
780         llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
781                                        Exp->getOpcode() == UnaryOperator::Imag);
782         llvm::Value *Ops[] = {Zero, Idx};
783         return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
784       }
785       case UnaryOperator::Deref:
786         // The address of a deref is just the value of the expression
787         return Visit(Exp->getSubExpr());
788       }
789       break;
790     }
791     }
792     CGM.WarnUnsupported(E, "constant l-value expression");
793     llvm::Type *Ty = llvm::PointerType::getUnqual(ConvertType(E->getType()));
794     return llvm::UndefValue::get(Ty);
795   }
796 
797 };
798 
799 }  // end anonymous namespace.
800 
801 
802 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
803                                                 CodeGenFunction *CGF) {
804   QualType type = Context.getCanonicalType(E->getType());
805 
806   if (type->isIntegerType()) {
807     llvm::APSInt Value(static_cast<uint32_t>(Context.getTypeSize(type)));
808     if (E->isIntegerConstantExpr(Value, Context)) {
809       return llvm::ConstantInt::get(Value);
810     }
811   }
812 
813   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
814   if (C->getType() == llvm::Type::Int1Ty) {
815     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
816     C = llvm::ConstantExpr::getZExt(C, BoolTy);
817   }
818   return C;
819 }
820