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/APValue.h"
18 #include "clang/AST/ASTContext.h"
19 #include "clang/AST/StmtVisitor.h"
20 #include "llvm/Constants.h"
21 #include "llvm/Function.h"
22 #include "llvm/GlobalVariable.h"
23 #include "llvm/Support/Compiler.h"
24 #include "llvm/Target/TargetData.h"
25 using namespace clang;
26 using namespace CodeGen;
27 
28 namespace  {
29 class VISIBILITY_HIDDEN ConstExprEmitter :
30   public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
31   CodeGenModule &CGM;
32   CodeGenFunction *CGF;
33 public:
34   ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
35     : CGM(cgm), CGF(cgf) {
36   }
37 
38   //===--------------------------------------------------------------------===//
39   //                            Visitor Methods
40   //===--------------------------------------------------------------------===//
41 
42   llvm::Constant *VisitStmt(Stmt *S) {
43     CGM.ErrorUnsupported(S, "constant expression");
44     QualType T = cast<Expr>(S)->getType();
45     return llvm::UndefValue::get(CGM.getTypes().ConvertType(T));
46   }
47 
48   llvm::Constant *VisitParenExpr(ParenExpr *PE) {
49     return Visit(PE->getSubExpr());
50   }
51 
52   // Leaves
53   llvm::Constant *VisitIntegerLiteral(const IntegerLiteral *E) {
54     return llvm::ConstantInt::get(E->getValue());
55   }
56   llvm::Constant *VisitFloatingLiteral(const FloatingLiteral *E) {
57     return llvm::ConstantFP::get(E->getValue());
58   }
59   llvm::Constant *VisitCharacterLiteral(const CharacterLiteral *E) {
60     return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
61   }
62   llvm::Constant *VisitCXXBoolLiteralExpr(const CXXBoolLiteralExpr *E) {
63     return llvm::ConstantInt::get(ConvertType(E->getType()), E->getValue());
64   }
65   llvm::Constant *VisitCXXZeroInitValueExpr(const CXXZeroInitValueExpr *E) {
66     return llvm::Constant::getNullValue(ConvertType(E->getType()));
67   }
68   llvm::Constant *VisitObjCStringLiteral(const ObjCStringLiteral *E) {
69     std::string S(E->getString()->getStrData(),
70                   E->getString()->getByteLength());
71     llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(S);
72     return llvm::ConstantExpr::getBitCast(C, ConvertType(E->getType()));
73   }
74 
75   llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
76     return Visit(E->getInitializer());
77   }
78 
79   llvm::Constant *VisitCastExpr(CastExpr* E) {
80     llvm::Constant *C = Visit(E->getSubExpr());
81 
82     return EmitConversion(C, E->getSubExpr()->getType(), E->getType());
83   }
84 
85   llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
86     return Visit(DAE->getExpr());
87   }
88 
89   llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
90     std::vector<llvm::Constant*> Elts;
91     const llvm::ArrayType *AType =
92         cast<llvm::ArrayType>(ConvertType(ILE->getType()));
93     unsigned NumInitElements = ILE->getNumInits();
94     // FIXME: Check for wide strings
95     if (NumInitElements > 0 && isa<StringLiteral>(ILE->getInit(0)) &&
96         ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
97       return Visit(ILE->getInit(0));
98     const llvm::Type *ElemTy = AType->getElementType();
99     unsigned NumElements = AType->getNumElements();
100 
101     // Initialising an array requires us to automatically
102     // initialise any elements that have not been initialised explicitly
103     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
104 
105     // Copy initializer elements.
106     unsigned i = 0;
107     bool RewriteType = false;
108     for (; i < NumInitableElts; ++i) {
109       llvm::Constant *C = Visit(ILE->getInit(i));
110       RewriteType |= (C->getType() != ElemTy);
111       Elts.push_back(C);
112     }
113 
114     // Initialize remaining array elements.
115     for (; i < NumElements; ++i)
116       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
117 
118     if (RewriteType) {
119       // FIXME: Try to avoid packing the array
120       std::vector<const llvm::Type*> Types;
121       for (unsigned i = 0; i < Elts.size(); ++i)
122         Types.push_back(Elts[i]->getType());
123       const llvm::StructType *SType = llvm::StructType::get(Types, true);
124       return llvm::ConstantStruct::get(SType, Elts);
125     }
126 
127     return llvm::ConstantArray::get(AType, Elts);
128   }
129 
130   void InsertBitfieldIntoStruct(std::vector<llvm::Constant*>& Elts,
131                                 FieldDecl* Field, Expr* E) {
132     // Calculate the value to insert
133     llvm::Constant *C = Visit(E);
134     llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
135     if (!CI) {
136       CGM.ErrorUnsupported(E, "bitfield initialization");
137       return;
138     }
139     llvm::APInt V = CI->getValue();
140 
141     // Calculate information about the relevant field
142     const llvm::Type* Ty = CI->getType();
143     const llvm::TargetData &TD = CGM.getTypes().getTargetData();
144     unsigned size = TD.getTypeStoreSizeInBits(Ty);
145     unsigned fieldOffset = CGM.getTypes().getLLVMFieldNo(Field) * size;
146     CodeGenTypes::BitFieldInfo bitFieldInfo =
147         CGM.getTypes().getBitFieldInfo(Field);
148     fieldOffset += bitFieldInfo.Begin;
149 
150     // Find where to start the insertion
151     // FIXME: This is O(n^2) in the number of bit-fields!
152     // FIXME: This won't work if the struct isn't completely packed!
153     unsigned offset = 0, i = 0;
154     while (offset < (fieldOffset & -8))
155       offset += TD.getTypeStoreSizeInBits(Elts[i++]->getType());
156 
157     // Advance over 0 sized elements (must terminate in bounds since
158     // the bitfield must have a size).
159     while (TD.getTypeStoreSizeInBits(Elts[i]->getType()) == 0)
160       ++i;
161 
162     // Promote the size of V if necessary
163     // FIXME: This should never occur, but currently it can because
164     // initializer constants are cast to bool, and because clang is
165     // not enforcing bitfield width limits.
166     if (bitFieldInfo.Size > V.getBitWidth())
167       V.zext(bitFieldInfo.Size);
168 
169     // Insert the bits into the struct
170     // FIXME: This algorthm is only correct on X86!
171     // FIXME: THis algorthm assumes bit-fields only have byte-size elements!
172     unsigned bitsToInsert = bitFieldInfo.Size;
173     unsigned curBits = std::min(8 - (fieldOffset & 7), bitsToInsert);
174     unsigned byte = V.getLoBits(curBits).getZExtValue() << (fieldOffset & 7);
175     do {
176       llvm::Constant* byteC = llvm::ConstantInt::get(llvm::Type::Int8Ty, byte);
177       Elts[i] = llvm::ConstantExpr::getOr(Elts[i], byteC);
178       ++i;
179       V = V.lshr(curBits);
180       bitsToInsert -= curBits;
181 
182       if (!bitsToInsert)
183         break;
184 
185       curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
186       byte = V.getLoBits(curBits).getZExtValue();
187     } while (true);
188   }
189 
190   llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
191     const llvm::StructType *SType =
192         cast<llvm::StructType>(ConvertType(ILE->getType()));
193     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
194     std::vector<llvm::Constant*> Elts;
195 
196     // Initialize the whole structure to zero.
197     for (unsigned i = 0; i < SType->getNumElements(); ++i) {
198       const llvm::Type *FieldTy = SType->getElementType(i);
199       Elts.push_back(llvm::Constant::getNullValue(FieldTy));
200     }
201 
202     // Copy initializer elements. Skip padding fields.
203     unsigned EltNo = 0;  // Element no in ILE
204     int FieldNo = 0; // Field no in RecordDecl
205     bool RewriteType = false;
206     while (EltNo < ILE->getNumInits() && FieldNo < RD->getNumMembers()) {
207       FieldDecl* curField = RD->getMember(FieldNo);
208       FieldNo++;
209       if (!curField->getIdentifier())
210         continue;
211 
212       if (curField->isBitField()) {
213         InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(EltNo));
214       } else {
215         unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(curField);
216         llvm::Constant* C = Visit(ILE->getInit(EltNo));
217         RewriteType |= (C->getType() != Elts[FieldNo]->getType());
218         Elts[FieldNo] = C;
219       }
220       EltNo++;
221     }
222 
223     if (RewriteType) {
224       // FIXME: Make this work for non-packed structs
225       assert(SType->isPacked() && "Cannot recreate unpacked structs");
226       std::vector<const llvm::Type*> Types;
227       for (unsigned i = 0; i < Elts.size(); ++i)
228         Types.push_back(Elts[i]->getType());
229       SType = llvm::StructType::get(Types, true);
230     }
231 
232     return llvm::ConstantStruct::get(SType, Elts);
233   }
234 
235   llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
236     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
237     const llvm::Type *Ty = ConvertType(ILE->getType());
238 
239     // Find the field decl we're initializing, if any
240     int FieldNo = 0; // Field no in RecordDecl
241     FieldDecl* curField = 0;
242     while (FieldNo < RD->getNumMembers()) {
243       curField = RD->getMember(FieldNo);
244       FieldNo++;
245       if (curField->getIdentifier())
246         break;
247     }
248 
249     if (!curField || !curField->getIdentifier() || ILE->getNumInits() == 0)
250       return llvm::Constant::getNullValue(Ty);
251 
252     if (curField->isBitField()) {
253       // Create a dummy struct for bit-field insertion
254       unsigned NumElts = CGM.getTargetData().getABITypeSize(Ty) / 8;
255       llvm::Constant* NV = llvm::Constant::getNullValue(llvm::Type::Int8Ty);
256       std::vector<llvm::Constant*> Elts(NumElts, NV);
257 
258       InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
259       const llvm::ArrayType *RetTy =
260           llvm::ArrayType::get(NV->getType(), NumElts);
261       return llvm::ConstantArray::get(RetTy, Elts);
262     }
263 
264     llvm::Constant *C = Visit(ILE->getInit(0));
265 
266     // Build a struct with the union sub-element as the first member,
267     // and padded to the appropriate size
268     std::vector<llvm::Constant*> Elts;
269     std::vector<const llvm::Type*> Types;
270     Elts.push_back(C);
271     Types.push_back(C->getType());
272     unsigned CurSize = CGM.getTargetData().getTypeStoreSize(C->getType());
273     unsigned TotalSize = CGM.getTargetData().getTypeStoreSize(Ty);
274     while (CurSize < TotalSize) {
275       Elts.push_back(llvm::Constant::getNullValue(llvm::Type::Int8Ty));
276       Types.push_back(llvm::Type::Int8Ty);
277       CurSize++;
278     }
279 
280     // This always generates a packed struct
281     // FIXME: Try to generate an unpacked struct when we can
282     llvm::StructType* STy = llvm::StructType::get(Types, true);
283     return llvm::ConstantStruct::get(STy, Elts);
284   }
285 
286   llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
287     const llvm::VectorType *VType =
288         cast<llvm::VectorType>(ConvertType(ILE->getType()));
289     const llvm::Type *ElemTy = VType->getElementType();
290     std::vector<llvm::Constant*> Elts;
291     unsigned NumElements = VType->getNumElements();
292     unsigned NumInitElements = ILE->getNumInits();
293 
294     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
295 
296     // Copy initializer elements.
297     unsigned i = 0;
298     for (; i < NumInitableElts; ++i) {
299       llvm::Constant *C = Visit(ILE->getInit(i));
300       Elts.push_back(C);
301     }
302 
303     for (; i < NumElements; ++i)
304       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
305 
306     return llvm::ConstantVector::get(VType, Elts);
307   }
308 
309   llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
310     if (ILE->getType()->isScalarType()) {
311       // We have a scalar in braces. Just use the first element.
312       if (ILE->getNumInits() > 0)
313         return Visit(ILE->getInit(0));
314 
315       const llvm::Type* RetTy = CGM.getTypes().ConvertType(ILE->getType());
316       return llvm::Constant::getNullValue(RetTy);
317     }
318 
319     if (ILE->getType()->isArrayType())
320       return EmitArrayInitialization(ILE);
321 
322     if (ILE->getType()->isStructureType())
323       return EmitStructInitialization(ILE);
324 
325     if (ILE->getType()->isUnionType())
326       return EmitUnionInitialization(ILE);
327 
328     if (ILE->getType()->isVectorType())
329       return EmitVectorInitialization(ILE);
330 
331     assert(0 && "Unable to handle InitListExpr");
332     // Get rid of control reaches end of void function warning.
333     // Not reached.
334     return 0;
335   }
336 
337   llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
338     Expr* SExpr = ICExpr->getSubExpr();
339     QualType SType = SExpr->getType();
340     llvm::Constant *C; // the intermediate expression
341     QualType T;        // the type of the intermediate expression
342     if (SType->isArrayType()) {
343       // Arrays decay to a pointer to the first element
344       // VLAs would require special handling, but they can't occur here
345       C = EmitLValue(SExpr);
346       llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
347       llvm::Constant *Ops[] = {Idx0, Idx0};
348       C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
349       T = CGM.getContext().getArrayDecayedType(SType);
350     } else if (SType->isFunctionType()) {
351       // Function types decay to a pointer to the function
352       C = EmitLValue(SExpr);
353       T = CGM.getContext().getPointerType(SType);
354     } else {
355       C = Visit(SExpr);
356       T = SType;
357     }
358 
359     // Perform the conversion; note that an implicit cast can both promote
360     // and convert an array/function
361     return EmitConversion(C, T, ICExpr->getType());
362   }
363 
364   llvm::Constant *VisitStringLiteral(StringLiteral *E) {
365     assert(!E->getType()->isPointerType() && "Strings are always arrays");
366 
367     // Otherwise this must be a string initializing an array in a static
368     // initializer.  Don't emit it as the address of the string, emit the string
369     // data itself as an inline array.
370     return llvm::ConstantArray::get(CGM.GetStringForStringLiteral(E), false);
371   }
372 
373   llvm::Constant *VisitDeclRefExpr(DeclRefExpr *E) {
374     const ValueDecl *Decl = E->getDecl();
375     if (const EnumConstantDecl *EC = dyn_cast<EnumConstantDecl>(Decl))
376       return llvm::ConstantInt::get(EC->getInitVal());
377     assert(0 && "Unsupported decl ref type!");
378     return 0;
379   }
380 
381   llvm::Constant *VisitSizeOfAlignOfTypeExpr(const SizeOfAlignOfTypeExpr *E) {
382     return EmitSizeAlignOf(E->getArgumentType(), E->getType(), E->isSizeOf());
383   }
384 
385   llvm::Constant *VisitAddrLabelExpr(const AddrLabelExpr *E) {
386     assert(CGF && "Invalid address of label expression outside function.");
387     llvm::Constant *C =
388       llvm::ConstantInt::get(llvm::Type::Int32Ty,
389                              CGF->GetIDForAddrOfLabel(E->getLabel()));
390     return llvm::ConstantExpr::getIntToPtr(C, ConvertType(E->getType()));
391   }
392 
393   // Unary operators
394   llvm::Constant *VisitUnaryPlus(const UnaryOperator *E) {
395     return Visit(E->getSubExpr());
396   }
397   llvm::Constant *VisitUnaryMinus(const UnaryOperator *E) {
398     return llvm::ConstantExpr::getNeg(Visit(E->getSubExpr()));
399   }
400   llvm::Constant *VisitUnaryNot(const UnaryOperator *E) {
401     return llvm::ConstantExpr::getNot(Visit(E->getSubExpr()));
402   }
403   llvm::Constant *VisitUnaryLNot(const UnaryOperator *E) {
404     llvm::Constant *SubExpr = Visit(E->getSubExpr());
405 
406     if (E->getSubExpr()->getType()->isRealFloatingType()) {
407       // Compare against 0.0 for fp scalars.
408       llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
409       SubExpr = llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UEQ, SubExpr,
410                                             Zero);
411     } else {
412       assert((E->getSubExpr()->getType()->isIntegerType() ||
413               E->getSubExpr()->getType()->isPointerType()) &&
414              "Unknown scalar type to convert");
415       // Compare against an integer or pointer null.
416       llvm::Constant *Zero = llvm::Constant::getNullValue(SubExpr->getType());
417       SubExpr = llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_EQ, SubExpr,
418                                             Zero);
419     }
420 
421     return llvm::ConstantExpr::getZExt(SubExpr, ConvertType(E->getType()));
422   }
423   llvm::Constant *VisitUnarySizeOf(const UnaryOperator *E) {
424     return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), true);
425   }
426   llvm::Constant *VisitUnaryAlignOf(const UnaryOperator *E) {
427     return EmitSizeAlignOf(E->getSubExpr()->getType(), E->getType(), false);
428   }
429   llvm::Constant *VisitUnaryAddrOf(const UnaryOperator *E) {
430     return EmitLValue(E->getSubExpr());
431   }
432   llvm::Constant *VisitUnaryOffsetOf(const UnaryOperator *E) {
433     int64_t Val = E->evaluateOffsetOf(CGM.getContext());
434 
435     assert(E->getType()->isIntegerType() && "Result type must be an integer!");
436 
437     uint32_t ResultWidth =
438       static_cast<uint32_t>(CGM.getContext().getTypeSize(E->getType()));
439     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
440   }
441 
442   llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
443     return Visit(E->getSubExpr());
444   }
445 
446   // Binary operators
447   llvm::Constant *VisitBinOr(const BinaryOperator *E) {
448     llvm::Constant *LHS = Visit(E->getLHS());
449     llvm::Constant *RHS = Visit(E->getRHS());
450 
451     return llvm::ConstantExpr::getOr(LHS, RHS);
452   }
453   llvm::Constant *VisitBinSub(const BinaryOperator *E) {
454     llvm::Constant *LHS = Visit(E->getLHS());
455     llvm::Constant *RHS = Visit(E->getRHS());
456 
457     if (!isa<llvm::PointerType>(RHS->getType())) {
458       // pointer - int
459       if (isa<llvm::PointerType>(LHS->getType())) {
460         llvm::Constant *Idx = llvm::ConstantExpr::getNeg(RHS);
461 
462         return llvm::ConstantExpr::getGetElementPtr(LHS, &Idx, 1);
463       }
464 
465       // int - int
466       return llvm::ConstantExpr::getSub(LHS, RHS);
467     }
468 
469     assert(isa<llvm::PointerType>(LHS->getType()));
470 
471     const llvm::Type *ResultType = ConvertType(E->getType());
472     const QualType Type = E->getLHS()->getType();
473     const QualType ElementType = Type->getAsPointerType()->getPointeeType();
474 
475     LHS = llvm::ConstantExpr::getPtrToInt(LHS, ResultType);
476     RHS = llvm::ConstantExpr::getPtrToInt(RHS, ResultType);
477 
478     llvm::Constant *sub = llvm::ConstantExpr::getSub(LHS, RHS);
479     llvm::Constant *size = EmitSizeAlignOf(ElementType, E->getType(), true);
480     return llvm::ConstantExpr::getSDiv(sub, size);
481   }
482 
483   llvm::Constant *VisitBinShl(const BinaryOperator *E) {
484     llvm::Constant *LHS = Visit(E->getLHS());
485     llvm::Constant *RHS = Visit(E->getRHS());
486 
487     // LLVM requires the LHS and RHS to be the same type: promote or truncate the
488     // RHS to the same size as the LHS.
489     if (LHS->getType() != RHS->getType())
490       RHS = llvm::ConstantExpr::getIntegerCast(RHS, LHS->getType(), false);
491 
492     return llvm::ConstantExpr::getShl(LHS, RHS);
493   }
494 
495   llvm::Constant *VisitBinMul(const BinaryOperator *E) {
496     llvm::Constant *LHS = Visit(E->getLHS());
497     llvm::Constant *RHS = Visit(E->getRHS());
498 
499     return llvm::ConstantExpr::getMul(LHS, RHS);
500   }
501 
502   llvm::Constant *VisitBinDiv(const BinaryOperator *E) {
503     llvm::Constant *LHS = Visit(E->getLHS());
504     llvm::Constant *RHS = Visit(E->getRHS());
505 
506     if (LHS->getType()->isFPOrFPVector())
507       return llvm::ConstantExpr::getFDiv(LHS, RHS);
508     else if (E->getType()->isUnsignedIntegerType())
509       return llvm::ConstantExpr::getUDiv(LHS, RHS);
510     else
511       return llvm::ConstantExpr::getSDiv(LHS, RHS);
512   }
513 
514   llvm::Constant *VisitBinAdd(const BinaryOperator *E) {
515     llvm::Constant *LHS = Visit(E->getLHS());
516     llvm::Constant *RHS = Visit(E->getRHS());
517 
518     if (!E->getType()->isPointerType())
519       return llvm::ConstantExpr::getAdd(LHS, RHS);
520 
521     llvm::Constant *Ptr, *Idx;
522     if (isa<llvm::PointerType>(LHS->getType())) { // pointer + int
523       Ptr = LHS;
524       Idx = RHS;
525     } else { // int + pointer
526       Ptr = RHS;
527       Idx = LHS;
528     }
529 
530     return llvm::ConstantExpr::getGetElementPtr(Ptr, &Idx, 1);
531   }
532 
533   llvm::Constant *VisitBinAnd(const BinaryOperator *E) {
534     llvm::Constant *LHS = Visit(E->getLHS());
535     llvm::Constant *RHS = Visit(E->getRHS());
536 
537     return llvm::ConstantExpr::getAnd(LHS, RHS);
538   }
539 
540   llvm::Constant *EmitCmp(const BinaryOperator *E,
541                           llvm::CmpInst::Predicate SignedPred,
542                           llvm::CmpInst::Predicate UnsignedPred,
543                           llvm::CmpInst::Predicate FloatPred) {
544     llvm::Constant *LHS = Visit(E->getLHS());
545     llvm::Constant *RHS = Visit(E->getRHS());
546     llvm::Constant *Result;
547     if (LHS->getType()->isInteger() ||
548         isa<llvm::PointerType>(LHS->getType())) {
549       if (E->getLHS()->getType()->isSignedIntegerType())
550         Result = llvm::ConstantExpr::getICmp(SignedPred, LHS, RHS);
551       else
552         Result = llvm::ConstantExpr::getICmp(UnsignedPred, LHS, RHS);
553     } else if (LHS->getType()->isFloatingPoint()) {
554       Result = llvm::ConstantExpr::getFCmp(FloatPred, LHS, RHS);
555     } else {
556       CGM.ErrorUnsupported(E, "constant expression");
557       Result = llvm::ConstantInt::getFalse();
558     }
559 
560     const llvm::Type* ResultType = ConvertType(E->getType());
561     return llvm::ConstantExpr::getZExtOrBitCast(Result, ResultType);
562   }
563 
564   llvm::Constant *VisitBinNE(const BinaryOperator *E) {
565     return EmitCmp(E, llvm::CmpInst::ICMP_NE, llvm::CmpInst::ICMP_NE,
566                    llvm::CmpInst::FCMP_ONE);
567   }
568 
569   llvm::Constant *VisitBinEQ(const BinaryOperator *E) {
570     return EmitCmp(E, llvm::CmpInst::ICMP_EQ, llvm::CmpInst::ICMP_EQ,
571                    llvm::CmpInst::FCMP_OEQ);
572   }
573 
574   llvm::Constant *VisitBinLT(const BinaryOperator *E) {
575     return EmitCmp(E, llvm::CmpInst::ICMP_SLT, llvm::CmpInst::ICMP_ULT,
576                    llvm::CmpInst::FCMP_OLT);
577   }
578 
579   llvm::Constant *VisitBinLE(const BinaryOperator *E) {
580     return EmitCmp(E, llvm::CmpInst::ICMP_SLE, llvm::CmpInst::ICMP_ULE,
581                    llvm::CmpInst::FCMP_OLE);
582   }
583 
584   llvm::Constant *VisitBinGT(const BinaryOperator *E) {
585     return EmitCmp(E, llvm::CmpInst::ICMP_SGT, llvm::CmpInst::ICMP_UGT,
586                    llvm::CmpInst::FCMP_OGT);
587   }
588 
589   llvm::Constant *VisitBinGE(const BinaryOperator *E) {
590     return EmitCmp(E, llvm::CmpInst::ICMP_SGE, llvm::CmpInst::ICMP_SGE,
591                    llvm::CmpInst::FCMP_OGE);
592   }
593 
594   llvm::Constant *VisitConditionalOperator(const ConditionalOperator *E) {
595     llvm::Constant *Cond = Visit(E->getCond());
596     llvm::Constant *CondVal = EmitConversionToBool(Cond, E->getType());
597     llvm::ConstantInt *CondValInt = dyn_cast<llvm::ConstantInt>(CondVal);
598     if (!CondValInt) {
599       CGM.ErrorUnsupported(E, "constant expression");
600       return llvm::Constant::getNullValue(ConvertType(E->getType()));
601     }
602     if (CondValInt->isOne()) {
603       if (E->getLHS())
604         return Visit(E->getLHS());
605       return Cond;
606     }
607 
608     return Visit(E->getRHS());
609   }
610 
611   llvm::Constant *VisitCallExpr(const CallExpr *E) {
612     APValue Result;
613     if (E->tryEvaluate(Result, CGM.getContext())) {
614       if (Result.isInt())
615         return llvm::ConstantInt::get(Result.getInt());
616       if (Result.isFloat())
617         return llvm::ConstantFP::get(Result.getFloat());
618     }
619 
620     CGM.ErrorUnsupported(E, "constant call expression");
621     return llvm::Constant::getNullValue(ConvertType(E->getType()));
622   }
623 
624   // Utility methods
625   const llvm::Type *ConvertType(QualType T) {
626     return CGM.getTypes().ConvertType(T);
627   }
628 
629   llvm::Constant *EmitConversionToBool(llvm::Constant *Src, QualType SrcType) {
630     assert(SrcType->isCanonical() && "EmitConversion strips typedefs");
631 
632     if (SrcType->isRealFloatingType()) {
633       // Compare against 0.0 for fp scalars.
634       llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
635       return llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UNE, Src, Zero);
636     }
637 
638     assert((SrcType->isIntegerType() || SrcType->isPointerType()) &&
639            "Unknown scalar type to convert");
640 
641     // Compare against an integer or pointer null.
642     llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
643     return llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_NE, Src, Zero);
644   }
645 
646   llvm::Constant *EmitConversion(llvm::Constant *Src, QualType SrcType,
647                                  QualType DstType) {
648     SrcType = CGM.getContext().getCanonicalType(SrcType);
649     DstType = CGM.getContext().getCanonicalType(DstType);
650     if (SrcType == DstType) return Src;
651 
652     // Handle conversions to bool first, they are special: comparisons against 0.
653     if (DstType->isBooleanType())
654       return EmitConversionToBool(Src, SrcType);
655 
656     const llvm::Type *DstTy = ConvertType(DstType);
657 
658     // Ignore conversions like int -> uint.
659     if (Src->getType() == DstTy)
660       return Src;
661 
662     // Handle pointer conversions next: pointers can only be converted to/from
663     // other pointers and integers.
664     if (isa<llvm::PointerType>(DstTy)) {
665       // The source value may be an integer, or a pointer.
666       if (isa<llvm::PointerType>(Src->getType()))
667         return llvm::ConstantExpr::getBitCast(Src, DstTy);
668       assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
669       return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
670     }
671 
672     if (isa<llvm::PointerType>(Src->getType())) {
673       // Must be an ptr to int cast.
674       assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
675       return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
676     }
677 
678     // A scalar source can be splatted to a vector of the same element type
679     if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
680       const llvm::VectorType *VT = cast<llvm::VectorType>(DstTy);
681       assert((VT->getElementType() == Src->getType()) &&
682              "Vector element type must match scalar type to splat.");
683       unsigned NumElements = DstType->getAsVectorType()->getNumElements();
684       llvm::SmallVector<llvm::Constant*, 16> Elements;
685       for (unsigned i = 0; i < NumElements; i++)
686         Elements.push_back(Src);
687 
688       return llvm::ConstantVector::get(&Elements[0], NumElements);
689     }
690 
691     if (isa<llvm::VectorType>(Src->getType()) ||
692         isa<llvm::VectorType>(DstTy)) {
693       return llvm::ConstantExpr::getBitCast(Src, DstTy);
694     }
695 
696     // Finally, we have the arithmetic types: real int/float.
697     if (isa<llvm::IntegerType>(Src->getType())) {
698       bool InputSigned = SrcType->isSignedIntegerType();
699       if (isa<llvm::IntegerType>(DstTy))
700         return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
701       else if (InputSigned)
702         return llvm::ConstantExpr::getSIToFP(Src, DstTy);
703       else
704         return llvm::ConstantExpr::getUIToFP(Src, DstTy);
705     }
706 
707     assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
708     if (isa<llvm::IntegerType>(DstTy)) {
709       if (DstType->isSignedIntegerType())
710         return llvm::ConstantExpr::getFPToSI(Src, DstTy);
711       else
712         return llvm::ConstantExpr::getFPToUI(Src, DstTy);
713     }
714 
715     assert(DstTy->isFloatingPoint() && "Unknown real conversion");
716     if (DstTy->getTypeID() < Src->getType()->getTypeID())
717       return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
718     else
719       return llvm::ConstantExpr::getFPExtend(Src, DstTy);
720   }
721 
722   llvm::Constant *EmitSizeAlignOf(QualType TypeToSize,
723                                   QualType RetType, bool isSizeOf) {
724     std::pair<uint64_t, unsigned> Info =
725       CGM.getContext().getTypeInfo(TypeToSize);
726 
727     uint64_t Val = isSizeOf ? Info.first : Info.second;
728     Val /= 8;  // Return size in bytes, not bits.
729 
730     assert(RetType->isIntegerType() && "Result type must be an integer!");
731 
732     uint32_t ResultWidth =
733       static_cast<uint32_t>(CGM.getContext().getTypeSize(RetType));
734     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
735   }
736 
737   llvm::Constant *EmitLValue(Expr *E) {
738     switch (E->getStmtClass()) {
739     default: break;
740     case Expr::ParenExprClass:
741       // Elide parenthesis
742       return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
743     case Expr::CompoundLiteralExprClass: {
744       // Note that due to the nature of compound literals, this is guaranteed
745       // to be the only use of the variable, so we just generate it here.
746       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
747       llvm::Constant* C = Visit(CLE->getInitializer());
748       C = new llvm::GlobalVariable(C->getType(),E->getType().isConstQualified(),
749                                    llvm::GlobalValue::InternalLinkage,
750                                    C, ".compoundliteral", &CGM.getModule());
751       return C;
752     }
753     case Expr::DeclRefExprClass: {
754       ValueDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
755       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
756         return CGM.GetAddrOfFunction(FD);
757       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
758         if (VD->isFileVarDecl())
759           return CGM.GetAddrOfGlobalVar(VD);
760         else if (VD->isBlockVarDecl()) {
761           assert(CGF && "Can't access static local vars without CGF");
762           return CGF->GetAddrOfStaticLocalVar(VD);
763         }
764       }
765       break;
766     }
767     case Expr::MemberExprClass: {
768       MemberExpr* ME = cast<MemberExpr>(E);
769       llvm::Constant *Base;
770       if (ME->isArrow())
771         Base = Visit(ME->getBase());
772       else
773         Base = EmitLValue(ME->getBase());
774 
775       unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(ME->getMemberDecl());
776       llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
777       llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
778                                                    FieldNumber);
779       llvm::Value *Ops[] = {Zero, Idx};
780       return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
781     }
782     case Expr::ArraySubscriptExprClass: {
783       ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
784       llvm::Constant *Base = Visit(ASExpr->getBase());
785       llvm::Constant *Index = Visit(ASExpr->getIdx());
786       assert(!ASExpr->getBase()->getType()->isVectorType() &&
787              "Taking the address of a vector component is illegal!");
788       return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
789     }
790     case Expr::StringLiteralClass:
791       return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
792     case Expr::UnaryOperatorClass: {
793       UnaryOperator *Exp = cast<UnaryOperator>(E);
794       switch (Exp->getOpcode()) {
795       default: break;
796       case UnaryOperator::Extension:
797         // Extension is just a wrapper for expressions
798         return EmitLValue(Exp->getSubExpr());
799       case UnaryOperator::Real:
800       case UnaryOperator::Imag: {
801         // The address of __real or __imag is just a GEP off the address
802         // of the internal expression
803         llvm::Constant* C = EmitLValue(Exp->getSubExpr());
804         llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
805         llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
806                                        Exp->getOpcode() == UnaryOperator::Imag);
807         llvm::Value *Ops[] = {Zero, Idx};
808         return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
809       }
810       case UnaryOperator::Deref:
811         // The address of a deref is just the value of the expression
812         return Visit(Exp->getSubExpr());
813       }
814       break;
815     }
816     }
817     CGM.ErrorUnsupported(E, "constant l-value expression");
818     llvm::Type *Ty = llvm::PointerType::getUnqual(ConvertType(E->getType()));
819     return llvm::UndefValue::get(Ty);
820   }
821 };
822 
823 }  // end anonymous namespace.
824 
825 
826 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
827                                                 CodeGenFunction *CGF) {
828   QualType type = Context.getCanonicalType(E->getType());
829 
830   if (type->isIntegerType()) {
831     llvm::APSInt Value(static_cast<uint32_t>(Context.getTypeSize(type)));
832     if (E->isIntegerConstantExpr(Value, Context)) {
833       return llvm::ConstantInt::get(Value);
834     }
835   }
836 
837   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
838   if (C->getType() == llvm::Type::Int1Ty) {
839     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
840     C = llvm::ConstantExpr::getZExt(C, BoolTy);
841   }
842   return C;
843 }
844