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.ErrorUnsupported(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.ErrorUnsupported(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   llvm::Constant *VisitAddrLabelExpr(const AddrLabelExpr *E) {
382     assert(CGF && "Invalid address of label expression outside function.");
383     llvm::Constant *C =
384       llvm::ConstantInt::get(llvm::Type::Int32Ty,
385                              CGF->GetIDForAddrOfLabel(E->getLabel()));
386     return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
387   }
388 
389   // Unary operators
390   llvm::Constant *VisitUnaryPlus(const UnaryOperator *E) {
391     return Visit(E->getSubExpr());
392   }
393   llvm::Constant *VisitUnaryMinus(const UnaryOperator *E) {
394     return llvm::ConstantExpr::getNeg(Visit(E->getSubExpr()));
395   }
396   llvm::Constant *VisitUnaryNot(const UnaryOperator *E) {
397     return llvm::ConstantExpr::getNot(Visit(E->getSubExpr()));
398   }
399   llvm::Constant *VisitUnaryLNot(const UnaryOperator *E) {
400     llvm::Constant *SubExpr = Visit(E->getSubExpr());
401 
402     if (E->getSubExpr()->getType()->isRealFloatingType()) {
403       // Compare against 0.0 for fp scalars.
404       llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
405       SubExpr = llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UEQ, SubExpr,
406                                             Zero);
407     } else {
408       assert((E->getSubExpr()->getType()->isIntegerType() ||
409               E->getSubExpr()->getType()->isPointerType()) &&
410              "Unknown scalar type to convert");
411       // Compare against an integer or pointer null.
412       llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
413       SubExpr = llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_EQ, SubExpr,
414                                             Zero);
415     }
416 
417     return llvm::ConstantExpr::getZExt(SubExpr, ConvertType(E->getType()));
418   }
419   llvm::Constant *VisitUnarySizeOf(const UnaryOperator *E) {
420     return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), true);
421   }
422   llvm::Constant *VisitUnaryAlignOf(const UnaryOperator *E) {
423     return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), false);
424   }
425   llvm::Constant *VisitUnaryAddrOf(const UnaryOperator *E) {
426     return EmitLValue(E->getSubExpr());
427   }
428   llvm::Constant *VisitUnaryOffsetOf(const UnaryOperator *E) {
429     int64_t Val = E->evaluateOffsetOf(CGM.getContext());
430 
431     assert(E->getType()->isIntegerType() && "Result type must be an integer!");
432 
433     uint32_t ResultWidth =
434       static_cast<uint32_t>(CGM.getContext().getTypeSize(E->getType()));
435     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
436   }
437 
438   llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
439     return Visit(E->getSubExpr());
440   }
441 
442   // Binary operators
443   llvm::Constant *VisitBinOr(const BinaryOperator *E) {
444     llvm::Constant *LHS = Visit(E->getLHS());
445     llvm::Constant *RHS = Visit(E->getRHS());
446 
447     return llvm::ConstantExpr::getOr(LHS, RHS);
448   }
449   llvm::Constant *VisitBinSub(const BinaryOperator *E) {
450     llvm::Constant *LHS = Visit(E->getLHS());
451     llvm::Constant *RHS = Visit(E->getRHS());
452 
453     if (!isa<llvm::PointerType>(RHS->getType())) {
454       // pointer - int
455       if (isa<llvm::PointerType>(LHS->getType())) {
456         llvm::Constant *Idx = llvm::ConstantExpr::getNeg(RHS);
457 
458         return llvm::ConstantExpr::getGetElementPtr(LHS, &Idx, 1);
459       }
460 
461       // int - int
462       return llvm::ConstantExpr::getSub(LHS, RHS);
463     }
464 
465     assert(isa<llvm::PointerType>(LHS->getType()));
466 
467     const llvm::Type *ResultType = ConvertType(E->getType());
468     const QualType Type = E->getLHS()->getType();
469     const QualType ElementType = Type->getAsPointerType()->getPointeeType();
470 
471     LHS = llvm::ConstantExpr::getPtrToInt(LHS, ResultType);
472     RHS = llvm::ConstantExpr::getPtrToInt(RHS, ResultType);
473 
474     llvm::Constant *sub = llvm::ConstantExpr::getSub(LHS, RHS);
475     llvm::Constant *size = EmitSizeAlignOf(ElementType, E->getType(), true);
476     return llvm::ConstantExpr::getSDiv(sub, size);
477   }
478 
479   llvm::Constant *VisitBinShl(const BinaryOperator *E) {
480     llvm::Constant *LHS = Visit(E->getLHS());
481     llvm::Constant *RHS = Visit(E->getRHS());
482 
483     // LLVM requires the LHS and RHS to be the same type: promote or truncate the
484     // RHS to the same size as the LHS.
485     if (LHS->getType() != RHS->getType())
486       RHS = llvm::ConstantExpr::getIntegerCast(RHS, LHS->getType(), false);
487 
488     return llvm::ConstantExpr::getShl(LHS, RHS);
489   }
490 
491   llvm::Constant *VisitBinMul(const BinaryOperator *E) {
492     llvm::Constant *LHS = Visit(E->getLHS());
493     llvm::Constant *RHS = Visit(E->getRHS());
494 
495     return llvm::ConstantExpr::getMul(LHS, RHS);
496   }
497 
498   llvm::Constant *VisitBinDiv(const BinaryOperator *E) {
499     llvm::Constant *LHS = Visit(E->getLHS());
500     llvm::Constant *RHS = Visit(E->getRHS());
501 
502     if (LHS->getType()->isFPOrFPVector())
503       return llvm::ConstantExpr::getFDiv(LHS, RHS);
504     else if (E->getType()->isUnsignedIntegerType())
505       return llvm::ConstantExpr::getUDiv(LHS, RHS);
506     else
507       return llvm::ConstantExpr::getSDiv(LHS, RHS);
508   }
509 
510   llvm::Constant *VisitBinAdd(const BinaryOperator *E) {
511     llvm::Constant *LHS = Visit(E->getLHS());
512     llvm::Constant *RHS = Visit(E->getRHS());
513 
514     if (!E->getType()->isPointerType())
515       return llvm::ConstantExpr::getAdd(LHS, RHS);
516 
517     llvm::Constant *Ptr, *Idx;
518     if (isa<llvm::PointerType>(LHS->getType())) { // pointer + int
519       Ptr = LHS;
520       Idx = RHS;
521     } else { // int + pointer
522       Ptr = RHS;
523       Idx = LHS;
524     }
525 
526     return llvm::ConstantExpr::getGetElementPtr(Ptr, &Idx, 1);
527   }
528 
529   llvm::Constant *VisitBinAnd(const BinaryOperator *E) {
530     llvm::Constant *LHS = Visit(E->getLHS());
531     llvm::Constant *RHS = Visit(E->getRHS());
532 
533     return llvm::ConstantExpr::getAnd(LHS, RHS);
534   }
535 
536   llvm::Constant *EmitCmp(const BinaryOperator *E,
537                           llvm::CmpInst::Predicate SignedPred,
538                           llvm::CmpInst::Predicate UnsignedPred,
539                           llvm::CmpInst::Predicate FloatPred) {
540     llvm::Constant *LHS = Visit(E->getLHS());
541     llvm::Constant *RHS = Visit(E->getRHS());
542     llvm::Constant *Result;
543     if (LHS->getType()->isInteger() ||
544         isa<llvm::PointerType>(LHS->getType())) {
545       if (E->getLHS()->getType()->isSignedIntegerType())
546         Result = llvm::ConstantExpr::getICmp(SignedPred, LHS, RHS);
547       else
548         Result = llvm::ConstantExpr::getICmp(UnsignedPred, LHS, RHS);
549     } else if (LHS->getType()->isFloatingPoint()) {
550       Result = llvm::ConstantExpr::getFCmp(FloatPred, LHS, RHS);
551     } else {
552       CGM.ErrorUnsupported(E, "constant expression");
553       Result = llvm::ConstantInt::getFalse();
554     }
555 
556     const llvm::Type* ResultType = ConvertType(E->getType());
557     return llvm::ConstantExpr::getZExtOrBitCast(Result, ResultType);
558   }
559 
560   llvm::Constant *VisitBinNE(const BinaryOperator *E) {
561     return EmitCmp(E, llvm::CmpInst::ICMP_NE, llvm::CmpInst::ICMP_NE,
562                    llvm::CmpInst::FCMP_ONE);
563   }
564 
565   llvm::Constant *VisitBinEQ(const BinaryOperator *E) {
566     return EmitCmp(E, llvm::CmpInst::ICMP_EQ, llvm::CmpInst::ICMP_EQ,
567                    llvm::CmpInst::FCMP_OEQ);
568   }
569 
570   llvm::Constant *VisitBinLT(const BinaryOperator *E) {
571     return EmitCmp(E, llvm::CmpInst::ICMP_SLT, llvm::CmpInst::ICMP_ULT,
572                    llvm::CmpInst::FCMP_OLT);
573   }
574 
575   llvm::Constant *VisitBinLE(const BinaryOperator *E) {
576     return EmitCmp(E, llvm::CmpInst::ICMP_SLE, llvm::CmpInst::ICMP_ULE,
577                    llvm::CmpInst::FCMP_OLE);
578   }
579 
580   llvm::Constant *VisitBinGT(const BinaryOperator *E) {
581     return EmitCmp(E, llvm::CmpInst::ICMP_SGT, llvm::CmpInst::ICMP_UGT,
582                    llvm::CmpInst::FCMP_OGT);
583   }
584 
585   llvm::Constant *VisitBinGE(const BinaryOperator *E) {
586     return EmitCmp(E, llvm::CmpInst::ICMP_SGE, llvm::CmpInst::ICMP_SGE,
587                    llvm::CmpInst::FCMP_OGE);
588   }
589 
590   llvm::Constant *VisitConditionalOperator(const ConditionalOperator *E) {
591     llvm::Constant *Cond = Visit(E->getCond());
592     llvm::Constant *CondVal = EmitConversionToBool(Cond, E->getType());
593     llvm::ConstantInt *CondValInt = dyn_cast<llvm::ConstantInt>(CondVal);
594     if (!CondValInt) {
595       CGM.ErrorUnsupported(E, "constant expression");
596       return llvm::Constant::getNullValue(ConvertType(E->getType()));
597     }
598     if (CondValInt->isOne()) {
599       if (E->getLHS())
600         return Visit(E->getLHS());
601       return Cond;
602     }
603 
604     return Visit(E->getRHS());
605   }
606 
607   // Utility methods
608   const llvm::Type *ConvertType(QualType T) {
609     return CGM.getTypes().ConvertType(T);
610   }
611 
612   llvm::Constant *EmitConversionToBool(llvm::Constant *Src, QualType SrcType) {
613     assert(SrcType->isCanonical() && "EmitConversion strips typedefs");
614 
615     if (SrcType->isRealFloatingType()) {
616       // Compare against 0.0 for fp scalars.
617       llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
618       return llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UNE, Src, Zero);
619     }
620 
621     assert((SrcType->isIntegerType() || SrcType->isPointerType()) &&
622            "Unknown scalar type to convert");
623 
624     // Compare against an integer or pointer null.
625     llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
626     return llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_NE, Src, Zero);
627   }
628 
629   llvm::Constant *EmitConversion(llvm::Constant *Src, QualType SrcType,
630                                  QualType DstType) {
631     SrcType = CGM.getContext().getCanonicalType(SrcType);
632     DstType = CGM.getContext().getCanonicalType(DstType);
633     if (SrcType == DstType) return Src;
634 
635     // Handle conversions to bool first, they are special: comparisons against 0.
636     if (DstType->isBooleanType())
637       return EmitConversionToBool(Src, SrcType);
638 
639     const llvm::Type *DstTy = ConvertType(DstType);
640 
641     // Ignore conversions like int -> uint.
642     if (Src->getType() == DstTy)
643       return Src;
644 
645     // Handle pointer conversions next: pointers can only be converted to/from
646     // other pointers and integers.
647     if (isa<llvm::PointerType>(DstTy)) {
648       // The source value may be an integer, or a pointer.
649       if (isa<llvm::PointerType>(Src->getType()))
650         return llvm::ConstantExpr::getBitCast(Src, DstTy);
651       assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
652       return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
653     }
654 
655     if (isa<llvm::PointerType>(Src->getType())) {
656       // Must be an ptr to int cast.
657       assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
658       return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
659     }
660 
661     // A scalar source can be splatted to a vector of the same element type
662     if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
663       const llvm::VectorType *VT = cast<llvm::VectorType>(DstTy);
664       assert((VT->getElementType() == Src->getType()) &&
665              "Vector element type must match scalar type to splat.");
666       unsigned NumElements = DstType->getAsVectorType()->getNumElements();
667       llvm::SmallVector<llvm::Constant*, 16> Elements;
668       for (unsigned i = 0; i < NumElements; i++)
669         Elements.push_back(Src);
670 
671       return llvm::ConstantVector::get(&Elements[0], NumElements);
672     }
673 
674     if (isa<llvm::VectorType>(Src->getType()) ||
675         isa<llvm::VectorType>(DstTy)) {
676       return llvm::ConstantExpr::getBitCast(Src, DstTy);
677     }
678 
679     // Finally, we have the arithmetic types: real int/float.
680     if (isa<llvm::IntegerType>(Src->getType())) {
681       bool InputSigned = SrcType->isSignedIntegerType();
682       if (isa<llvm::IntegerType>(DstTy))
683         return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
684       else if (InputSigned)
685         return llvm::ConstantExpr::getSIToFP(Src, DstTy);
686       else
687         return llvm::ConstantExpr::getUIToFP(Src, DstTy);
688     }
689 
690     assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
691     if (isa<llvm::IntegerType>(DstTy)) {
692       if (DstType->isSignedIntegerType())
693         return llvm::ConstantExpr::getFPToSI(Src, DstTy);
694       else
695         return llvm::ConstantExpr::getFPToUI(Src, DstTy);
696     }
697 
698     assert(DstTy->isFloatingPoint() && "Unknown real conversion");
699     if (DstTy->getTypeID() < Src->getType()->getTypeID())
700       return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
701     else
702       return llvm::ConstantExpr::getFPExtend(Src, DstTy);
703   }
704 
705   llvm::Constant *EmitSizeAlignOf(QualType TypeToSize,
706                                   QualType RetType, bool isSizeOf) {
707     std::pair<uint64_t, unsigned> Info =
708       CGM.getContext().getTypeInfo(TypeToSize);
709 
710     uint64_t Val = isSizeOf ? Info.first : Info.second;
711     Val /= 8;  // Return size in bytes, not bits.
712 
713     assert(RetType->isIntegerType() && "Result type must be an integer!");
714 
715     uint32_t ResultWidth =
716       static_cast<uint32_t>(CGM.getContext().getTypeSize(RetType));
717     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
718   }
719 
720   llvm::Constant *EmitLValue(Expr *E) {
721     switch (E->getStmtClass()) {
722     default: break;
723     case Expr::ParenExprClass:
724       // Elide parenthesis
725       return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
726     case Expr::CompoundLiteralExprClass: {
727       // Note that due to the nature of compound literals, this is guaranteed
728       // to be the only use of the variable, so we just generate it here.
729       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
730       llvm::Constant* C = Visit(CLE->getInitializer());
731       C = new llvm::GlobalVariable(C->getType(),E->getType().isConstQualified(),
732                                    llvm::GlobalValue::InternalLinkage,
733                                    C, ".compoundliteral", &CGM.getModule());
734       return C;
735     }
736     case Expr::DeclRefExprClass: {
737       ValueDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
738       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
739         return CGM.GetAddrOfFunction(FD);
740       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
741         if (VD->isFileVarDecl())
742           return CGM.GetAddrOfGlobalVar(VD);
743         else if (VD->isBlockVarDecl()) {
744           assert(CGF && "Can't access static local vars without CGF");
745           return CGF->GetAddrOfStaticLocalVar(VD);
746         }
747       }
748       break;
749     }
750     case Expr::MemberExprClass: {
751       MemberExpr* ME = cast<MemberExpr>(E);
752       llvm::Constant *Base;
753       if (ME->isArrow())
754         Base = Visit(ME->getBase());
755       else
756         Base = EmitLValue(ME->getBase());
757 
758       unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(ME->getMemberDecl());
759       llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
760       llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
761                                                    FieldNumber);
762       llvm::Value *Ops[] = {Zero, Idx};
763       return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
764     }
765     case Expr::ArraySubscriptExprClass: {
766       ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
767       llvm::Constant *Base = Visit(ASExpr->getBase());
768       llvm::Constant *Index = Visit(ASExpr->getIdx());
769       assert(!ASExpr->getBase()->getType()->isVectorType() &&
770              "Taking the address of a vector component is illegal!");
771       return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
772     }
773     case Expr::StringLiteralClass:
774       return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
775     case Expr::UnaryOperatorClass: {
776       UnaryOperator *Exp = cast<UnaryOperator>(E);
777       switch (Exp->getOpcode()) {
778       default: break;
779       case UnaryOperator::Extension:
780         // Extension is just a wrapper for expressions
781         return EmitLValue(Exp->getSubExpr());
782       case UnaryOperator::Real:
783       case UnaryOperator::Imag: {
784         // The address of __real or __imag is just a GEP off the address
785         // of the internal expression
786         llvm::Constant* C = EmitLValue(Exp->getSubExpr());
787         llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
788         llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
789                                        Exp->getOpcode() == UnaryOperator::Imag);
790         llvm::Value *Ops[] = {Zero, Idx};
791         return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
792       }
793       case UnaryOperator::Deref:
794         // The address of a deref is just the value of the expression
795         return Visit(Exp->getSubExpr());
796       }
797       break;
798     }
799     }
800     CGM.ErrorUnsupported(E, "constant l-value expression");
801     llvm::Type *Ty = llvm::PointerType::getUnqual(ConvertType(E->getType()));
802     return llvm::UndefValue::get(Ty);
803   }
804 
805 };
806 
807 }  // end anonymous namespace.
808 
809 
810 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
811                                                 CodeGenFunction *CGF) {
812   QualType type = Context.getCanonicalType(E->getType());
813 
814   if (type->isIntegerType()) {
815     llvm::APSInt Value(static_cast<uint32_t>(Context.getTypeSize(type)));
816     if (E->isIntegerConstantExpr(Value, Context)) {
817       return llvm::ConstantInt::get(Value);
818     }
819   }
820 
821   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
822   if (C->getType() == llvm::Type::Int1Ty) {
823     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
824     C = llvm::ConstantExpr::getZExt(C, BoolTy);
825   }
826   return C;
827 }
828