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