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   llvm::Constant *VisitObjCStringLiteral(const ObjCStringLiteral *E) {
63     return CGM.getObjCRuntime()->GenerateConstantString(
64         E->getString()->getStrData(), E->getString()->getByteLength());
65   }
66 
67   llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
68     return Visit(E->getInitializer());
69   }
70 
71   llvm::Constant *VisitCastExpr(const CastExpr* E) {
72     llvm::Constant *C = Visit(E->getSubExpr());
73 
74     return EmitConversion(C, E->getSubExpr()->getType(), E->getType());
75   }
76 
77   llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
78     return Visit(DAE->getExpr());
79   }
80 
81   llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
82     std::vector<llvm::Constant*> Elts;
83     const llvm::ArrayType *AType =
84         cast<llvm::ArrayType>(ConvertType(ILE->getType()));
85     unsigned NumInitElements = ILE->getNumInits();
86     // FIXME: Check for wide strings
87     if (NumInitElements > 0 && isa<StringLiteral>(ILE->getInit(0)) &&
88         ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
89       return Visit(ILE->getInit(0));
90     const llvm::Type *ElemTy = AType->getElementType();
91     unsigned NumElements = AType->getNumElements();
92 
93     // Initialising an array requires us to automatically
94     // initialise any elements that have not been initialised explicitly
95     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
96 
97     // Copy initializer elements.
98     unsigned i = 0;
99     bool RewriteType = false;
100     for (; i < NumInitableElts; ++i) {
101       llvm::Constant *C = Visit(ILE->getInit(i));
102       RewriteType |= (C->getType() != ElemTy);
103       Elts.push_back(C);
104     }
105 
106     // Initialize remaining array elements.
107     for (; i < NumElements; ++i)
108       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
109 
110     if (RewriteType) {
111       // FIXME: Try to avoid packing the array
112       std::vector<const llvm::Type*> Types;
113       for (unsigned i = 0; i < Elts.size(); ++i)
114         Types.push_back(Elts[i]->getType());
115       const llvm::StructType *SType = llvm::StructType::get(Types, true);
116       return llvm::ConstantStruct::get(SType, Elts);
117     }
118 
119     return llvm::ConstantArray::get(AType, Elts);
120   }
121 
122   void InsertBitfieldIntoStruct(std::vector<llvm::Constant*>& Elts,
123                                 FieldDecl* Field, Expr* E) {
124     // Calculate the value to insert
125     llvm::Constant *C = Visit(E);
126     llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
127     if (!CI) {
128       CGM.WarnUnsupported(E, "bitfield initialization");
129       return;
130     }
131     llvm::APInt V = CI->getValue();
132 
133     // Calculate information about the relevant field
134     const llvm::Type* Ty = CI->getType();
135     const llvm::TargetData &TD = CGM.getTypes().getTargetData();
136     unsigned size = TD.getTypeStoreSizeInBits(Ty);
137     unsigned fieldOffset = CGM.getTypes().getLLVMFieldNo(Field) * size;
138     CodeGenTypes::BitFieldInfo bitFieldInfo =
139         CGM.getTypes().getBitFieldInfo(Field);
140     fieldOffset += bitFieldInfo.Begin;
141 
142     // Find where to start the insertion
143     // FIXME: This is O(n^2) in the number of bit-fields!
144     // FIXME: This won't work if the struct isn't completely packed!
145     unsigned offset = 0, i = 0;
146     while (offset < (fieldOffset & -8))
147       offset += TD.getTypeStoreSizeInBits(Elts[i++]->getType());
148 
149     // Advance over 0 sized elements (must terminate in bounds since
150     // the bitfield must have a size).
151     while (TD.getTypeStoreSizeInBits(Elts[i]->getType()) == 0)
152       ++i;
153 
154     // Promote the size of V if necessary
155     // FIXME: This should never occur, but currently it can because
156     // initializer constants are cast to bool, and because clang is
157     // not enforcing bitfield width limits.
158     if (bitFieldInfo.Size > V.getBitWidth())
159       V.zext(bitFieldInfo.Size);
160 
161     // Insert the bits into the struct
162     // FIXME: This algorthm is only correct on X86!
163     // FIXME: THis algorthm assumes bit-fields only have byte-size elements!
164     unsigned bitsToInsert = bitFieldInfo.Size;
165     unsigned curBits = std::min(8 - (fieldOffset & 7), bitsToInsert);
166     unsigned byte = V.getLoBits(curBits).getZExtValue() << (fieldOffset & 7);
167     do {
168       llvm::Constant* byteC = llvm::ConstantInt::get(llvm::Type::Int8Ty, byte);
169       Elts[i] = llvm::ConstantExpr::getOr(Elts[i], byteC);
170       ++i;
171       V = V.lshr(curBits);
172       bitsToInsert -= curBits;
173 
174       if (!bitsToInsert)
175         break;
176 
177       curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
178       byte = V.getLoBits(curBits).getZExtValue();
179     } while (true);
180   }
181 
182   llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
183     const llvm::StructType *SType =
184         cast<llvm::StructType>(ConvertType(ILE->getType()));
185     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
186     std::vector<llvm::Constant*> Elts;
187 
188     // Initialize the whole structure to zero.
189     for (unsigned i = 0; i < SType->getNumElements(); ++i) {
190       const llvm::Type *FieldTy = SType->getElementType(i);
191       Elts.push_back(llvm::Constant::getNullValue(FieldTy));
192     }
193 
194     // Copy initializer elements. Skip padding fields.
195     unsigned EltNo = 0;  // Element no in ILE
196     int FieldNo = 0; // Field no in RecordDecl
197     bool RewriteType = false;
198     while (EltNo < ILE->getNumInits() && FieldNo < RD->getNumMembers()) {
199       FieldDecl* curField = RD->getMember(FieldNo);
200       FieldNo++;
201       if (!curField->getIdentifier())
202         continue;
203 
204       if (curField->isBitField()) {
205         InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(EltNo));
206       } else {
207         unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(curField);
208         llvm::Constant* C = Visit(ILE->getInit(EltNo));
209         RewriteType |= (C->getType() != Elts[FieldNo]->getType());
210         Elts[FieldNo] = C;
211       }
212       EltNo++;
213     }
214 
215     if (RewriteType) {
216       // FIXME: Make this work for non-packed structs
217       assert(SType->isPacked() && "Cannot recreate unpacked structs");
218       std::vector<const llvm::Type*> Types;
219       for (unsigned i = 0; i < Elts.size(); ++i)
220         Types.push_back(Elts[i]->getType());
221       SType = llvm::StructType::get(Types, true);
222     }
223 
224     return llvm::ConstantStruct::get(SType, Elts);
225   }
226 
227   llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
228     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
229     const llvm::Type *Ty = ConvertType(ILE->getType());
230 
231     // Find the field decl we're initializing, if any
232     int FieldNo = 0; // Field no in RecordDecl
233     FieldDecl* curField = 0;
234     while (FieldNo < RD->getNumMembers()) {
235       curField = RD->getMember(FieldNo);
236       FieldNo++;
237       if (curField->getIdentifier())
238         break;
239     }
240 
241     if (!curField || !curField->getIdentifier() || ILE->getNumInits() == 0)
242       return llvm::Constant::getNullValue(Ty);
243 
244     if (curField->isBitField()) {
245       // Create a dummy struct for bit-field insertion
246       unsigned NumElts = CGM.getTargetData().getABITypeSize(Ty) / 8;
247       llvm::Constant* NV = llvm::Constant::getNullValue(llvm::Type::Int8Ty);
248       std::vector<llvm::Constant*> Elts(NumElts, NV);
249 
250       InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
251       const llvm::ArrayType *RetTy =
252           llvm::ArrayType::get(NV->getType(), NumElts);
253       return llvm::ConstantArray::get(RetTy, Elts);
254     }
255 
256     llvm::Constant *C = Visit(ILE->getInit(0));
257 
258     // Build a struct with the union sub-element as the first member,
259     // and padded to the appropriate size
260     std::vector<llvm::Constant*> Elts;
261     std::vector<const llvm::Type*> Types;
262     Elts.push_back(C);
263     Types.push_back(C->getType());
264     unsigned CurSize = CGM.getTargetData().getTypeStoreSize(C->getType());
265     unsigned TotalSize = CGM.getTargetData().getTypeStoreSize(Ty);
266     while (CurSize < TotalSize) {
267       Elts.push_back(llvm::Constant::getNullValue(llvm::Type::Int8Ty));
268       Types.push_back(llvm::Type::Int8Ty);
269       CurSize++;
270     }
271 
272     // This always generates a packed struct
273     // FIXME: Try to generate an unpacked struct when we can
274     llvm::StructType* STy = llvm::StructType::get(Types, true);
275     return llvm::ConstantStruct::get(STy, Elts);
276   }
277 
278   llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
279     const llvm::VectorType *VType =
280         cast<llvm::VectorType>(ConvertType(ILE->getType()));
281     const llvm::Type *ElemTy = VType->getElementType();
282     std::vector<llvm::Constant*> Elts;
283     unsigned NumElements = VType->getNumElements();
284     unsigned NumInitElements = ILE->getNumInits();
285 
286     unsigned NumInitableElts = std::min(NumInitElements, NumElements);
287 
288     // Copy initializer elements.
289     unsigned i = 0;
290     for (; i < NumInitableElts; ++i) {
291       llvm::Constant *C = Visit(ILE->getInit(i));
292       Elts.push_back(C);
293     }
294 
295     for (; i < NumElements; ++i)
296       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
297 
298     return llvm::ConstantVector::get(VType, Elts);
299   }
300 
301   llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
302     if (ILE->getType()->isScalarType()) {
303       // We have a scalar in braces. Just use the first element.
304       if (ILE->getNumInits() > 0)
305         return Visit(ILE->getInit(0));
306 
307       const llvm::Type* RetTy = CGM.getTypes().ConvertType(ILE->getType());
308       return llvm::Constant::getNullValue(RetTy);
309     }
310 
311     if (ILE->getType()->isArrayType())
312       return EmitArrayInitialization(ILE);
313 
314     if (ILE->getType()->isStructureType())
315       return EmitStructInitialization(ILE);
316 
317     if (ILE->getType()->isUnionType())
318       return EmitUnionInitialization(ILE);
319 
320     if (ILE->getType()->isVectorType())
321       return EmitVectorInitialization(ILE);
322 
323     assert(0 && "Unable to handle InitListExpr");
324     // Get rid of control reaches end of void function warning.
325     // Not reached.
326     return 0;
327   }
328 
329   llvm::Constant *VisitImplicitCastExpr(ImplicitCastExpr *ICExpr) {
330     Expr* SExpr = ICExpr->getSubExpr();
331     QualType SType = SExpr->getType();
332     llvm::Constant *C; // the intermediate expression
333     QualType T;        // the type of the intermediate expression
334     if (SType->isArrayType()) {
335       // Arrays decay to a pointer to the first element
336       // VLAs would require special handling, but they can't occur here
337       C = EmitLValue(SExpr);
338       llvm::Constant *Idx0 = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
339       llvm::Constant *Ops[] = {Idx0, Idx0};
340       C = llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
341       T = CGM.getContext().getArrayDecayedType(SType);
342     } else if (SType->isFunctionType()) {
343       // Function types decay to a pointer to the function
344       C = EmitLValue(SExpr);
345       T = CGM.getContext().getPointerType(SType);
346     } else {
347       C = Visit(SExpr);
348       T = SType;
349     }
350 
351     // Perform the conversion; note that an implicit cast can both promote
352     // and convert an array/function
353     return EmitConversion(C, T, ICExpr->getType());
354   }
355 
356   llvm::Constant *VisitStringLiteral(StringLiteral *E) {
357     const char *StrData = E->getStrData();
358     unsigned Len = E->getByteLength();
359     assert(!E->getType()->isPointerType() && "Strings are always arrays");
360 
361     // Otherwise this must be a string initializing an array in a static
362     // initializer.  Don't emit it as the address of the string, emit the string
363     // data itself as an inline array.
364     const ConstantArrayType *CAT =
365       CGM.getContext().getAsConstantArrayType(E->getType());
366     assert(CAT && "String isn't pointer or array!");
367 
368     std::string Str(StrData, StrData + Len);
369     // Null terminate the string before potentially truncating it.
370     // FIXME: What about wchar_t strings?
371     Str.push_back(0);
372 
373     uint64_t RealLen = CAT->getSize().getZExtValue();
374     // String or grow the initializer to the required size.
375     if (RealLen != Str.size())
376       Str.resize(RealLen);
377 
378     return llvm::ConstantArray::get(Str, false);
379   }
380 
381   llvm::Constant *VisitDeclRefExpr(DeclRefExpr *E) {
382     const ValueDecl *Decl = E->getDecl();
383     if (const EnumConstantDecl *EC = dyn_cast<EnumConstantDecl>(Decl))
384       return llvm::ConstantInt::get(EC->getInitVal());
385     assert(0 && "Unsupported decl ref type!");
386     return 0;
387   }
388 
389   llvm::Constant *VisitSizeOfAlignOfTypeExpr(const SizeOfAlignOfTypeExpr *E) {
390     return EmitSizeAlignOf(E->getArgumentType(), E->getType(), E->isSizeOf());
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.WarnUnsupported(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.WarnUnsupported(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   // Utility methods
612   const llvm::Type *ConvertType(QualType T) {
613     return CGM.getTypes().ConvertType(T);
614   }
615 
616   llvm::Constant *EmitConversionToBool(llvm::Constant *Src, QualType SrcType) {
617     assert(SrcType->isCanonical() && "EmitConversion strips typedefs");
618 
619     if (SrcType->isRealFloatingType()) {
620       // Compare against 0.0 for fp scalars.
621       llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
622       return llvm::ConstantExpr::getFCmp(llvm::FCmpInst::FCMP_UNE, Src, Zero);
623     }
624 
625     assert((SrcType->isIntegerType() || SrcType->isPointerType()) &&
626            "Unknown scalar type to convert");
627 
628     // Compare against an integer or pointer null.
629     llvm::Constant *Zero = llvm::Constant::getNullValue(Src->getType());
630     return llvm::ConstantExpr::getICmp(llvm::ICmpInst::ICMP_NE, Src, Zero);
631   }
632 
633   llvm::Constant *EmitConversion(llvm::Constant *Src, QualType SrcType,
634                                  QualType DstType) {
635     SrcType = CGM.getContext().getCanonicalType(SrcType);
636     DstType = CGM.getContext().getCanonicalType(DstType);
637     if (SrcType == DstType) return Src;
638 
639     // Handle conversions to bool first, they are special: comparisons against 0.
640     if (DstType->isBooleanType())
641       return EmitConversionToBool(Src, SrcType);
642 
643     const llvm::Type *DstTy = ConvertType(DstType);
644 
645     // Ignore conversions like int -> uint.
646     if (Src->getType() == DstTy)
647       return Src;
648 
649     // Handle pointer conversions next: pointers can only be converted to/from
650     // other pointers and integers.
651     if (isa<llvm::PointerType>(DstTy)) {
652       // The source value may be an integer, or a pointer.
653       if (isa<llvm::PointerType>(Src->getType()))
654         return llvm::ConstantExpr::getBitCast(Src, DstTy);
655       assert(SrcType->isIntegerType() &&"Not ptr->ptr or int->ptr conversion?");
656       return llvm::ConstantExpr::getIntToPtr(Src, DstTy);
657     }
658 
659     if (isa<llvm::PointerType>(Src->getType())) {
660       // Must be an ptr to int cast.
661       assert(isa<llvm::IntegerType>(DstTy) && "not ptr->int?");
662       return llvm::ConstantExpr::getPtrToInt(Src, DstTy);
663     }
664 
665     // A scalar source can be splatted to a vector of the same element type
666     if (isa<llvm::VectorType>(DstTy) && !isa<VectorType>(SrcType)) {
667       const llvm::VectorType *VT = cast<llvm::VectorType>(DstTy);
668       assert((VT->getElementType() == Src->getType()) &&
669              "Vector element type must match scalar type to splat.");
670       unsigned NumElements = DstType->getAsVectorType()->getNumElements();
671       llvm::SmallVector<llvm::Constant*, 16> Elements;
672       for (unsigned i = 0; i < NumElements; i++)
673         Elements.push_back(Src);
674 
675       return llvm::ConstantVector::get(&Elements[0], NumElements);
676     }
677 
678     if (isa<llvm::VectorType>(Src->getType()) ||
679         isa<llvm::VectorType>(DstTy)) {
680       return llvm::ConstantExpr::getBitCast(Src, DstTy);
681     }
682 
683     // Finally, we have the arithmetic types: real int/float.
684     if (isa<llvm::IntegerType>(Src->getType())) {
685       bool InputSigned = SrcType->isSignedIntegerType();
686       if (isa<llvm::IntegerType>(DstTy))
687         return llvm::ConstantExpr::getIntegerCast(Src, DstTy, InputSigned);
688       else if (InputSigned)
689         return llvm::ConstantExpr::getSIToFP(Src, DstTy);
690       else
691         return llvm::ConstantExpr::getUIToFP(Src, DstTy);
692     }
693 
694     assert(Src->getType()->isFloatingPoint() && "Unknown real conversion");
695     if (isa<llvm::IntegerType>(DstTy)) {
696       if (DstType->isSignedIntegerType())
697         return llvm::ConstantExpr::getFPToSI(Src, DstTy);
698       else
699         return llvm::ConstantExpr::getFPToUI(Src, DstTy);
700     }
701 
702     assert(DstTy->isFloatingPoint() && "Unknown real conversion");
703     if (DstTy->getTypeID() < Src->getType()->getTypeID())
704       return llvm::ConstantExpr::getFPTrunc(Src, DstTy);
705     else
706       return llvm::ConstantExpr::getFPExtend(Src, DstTy);
707   }
708 
709   llvm::Constant *EmitSizeAlignOf(QualType TypeToSize,
710                                   QualType RetType, bool isSizeOf) {
711     std::pair<uint64_t, unsigned> Info =
712       CGM.getContext().getTypeInfo(TypeToSize);
713 
714     uint64_t Val = isSizeOf ? Info.first : Info.second;
715     Val /= 8;  // Return size in bytes, not bits.
716 
717     assert(RetType->isIntegerType() && "Result type must be an integer!");
718 
719     uint32_t ResultWidth =
720       static_cast<uint32_t>(CGM.getContext().getTypeSize(RetType));
721     return llvm::ConstantInt::get(llvm::APInt(ResultWidth, Val));
722   }
723 
724   llvm::Constant *EmitLValue(Expr *E) {
725     switch (E->getStmtClass()) {
726     default: break;
727     case Expr::ParenExprClass:
728       // Elide parenthesis
729       return EmitLValue(cast<ParenExpr>(E)->getSubExpr());
730     case Expr::CompoundLiteralExprClass: {
731       // Note that due to the nature of compound literals, this is guaranteed
732       // to be the only use of the variable, so we just generate it here.
733       CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
734       llvm::Constant* C = Visit(CLE->getInitializer());
735       C = new llvm::GlobalVariable(C->getType(),E->getType().isConstQualified(),
736                                    llvm::GlobalValue::InternalLinkage,
737                                    C, ".compoundliteral", &CGM.getModule());
738       return C;
739     }
740     case Expr::DeclRefExprClass: {
741       ValueDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
742       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
743         return CGM.GetAddrOfFunction(FD);
744       if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
745         if (VD->isFileVarDecl())
746           return CGM.GetAddrOfGlobalVar(VD);
747         else if (VD->isBlockVarDecl()) {
748           assert(CGF && "Can't access static local vars without CGF");
749           return CGF->GetAddrOfStaticLocalVar(VD);
750         }
751       }
752       break;
753     }
754     case Expr::MemberExprClass: {
755       MemberExpr* ME = cast<MemberExpr>(E);
756       llvm::Constant *Base;
757       if (ME->isArrow())
758         Base = Visit(ME->getBase());
759       else
760         Base = EmitLValue(ME->getBase());
761 
762       unsigned FieldNumber = CGM.getTypes().getLLVMFieldNo(ME->getMemberDecl());
763       llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
764       llvm::Constant *Idx = llvm::ConstantInt::get(llvm::Type::Int32Ty,
765                                                    FieldNumber);
766       llvm::Value *Ops[] = {Zero, Idx};
767       return llvm::ConstantExpr::getGetElementPtr(Base, Ops, 2);
768     }
769     case Expr::ArraySubscriptExprClass: {
770       ArraySubscriptExpr* ASExpr = cast<ArraySubscriptExpr>(E);
771       llvm::Constant *Base = Visit(ASExpr->getBase());
772       llvm::Constant *Index = Visit(ASExpr->getIdx());
773       assert(!ASExpr->getBase()->getType()->isVectorType() &&
774              "Taking the address of a vector component is illegal!");
775       return llvm::ConstantExpr::getGetElementPtr(Base, &Index, 1);
776     }
777     case Expr::StringLiteralClass: {
778       StringLiteral *String = cast<StringLiteral>(E);
779       assert(!String->isWide() && "Cannot codegen wide strings yet");
780       const char *StrData = String->getStrData();
781       unsigned Len = String->getByteLength();
782 
783       return CGM.GetAddrOfConstantString(std::string(StrData, StrData + Len));
784     }
785     case Expr::UnaryOperatorClass: {
786       UnaryOperator *Exp = cast<UnaryOperator>(E);
787       switch (Exp->getOpcode()) {
788       default: break;
789       case UnaryOperator::Extension:
790         // Extension is just a wrapper for expressions
791         return EmitLValue(Exp->getSubExpr());
792       case UnaryOperator::Real:
793       case UnaryOperator::Imag: {
794         // The address of __real or __imag is just a GEP off the address
795         // of the internal expression
796         llvm::Constant* C = EmitLValue(Exp->getSubExpr());
797         llvm::Constant *Zero = llvm::ConstantInt::get(llvm::Type::Int32Ty, 0);
798         llvm::Constant *Idx  = llvm::ConstantInt::get(llvm::Type::Int32Ty,
799                                        Exp->getOpcode() == UnaryOperator::Imag);
800         llvm::Value *Ops[] = {Zero, Idx};
801         return llvm::ConstantExpr::getGetElementPtr(C, Ops, 2);
802       }
803       case UnaryOperator::Deref:
804         // The address of a deref is just the value of the expression
805         return Visit(Exp->getSubExpr());
806       }
807       break;
808     }
809     }
810     CGM.WarnUnsupported(E, "constant l-value expression");
811     llvm::Type *Ty = llvm::PointerType::getUnqual(ConvertType(E->getType()));
812     return llvm::UndefValue::get(Ty);
813   }
814 
815 };
816 
817 }  // end anonymous namespace.
818 
819 
820 llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
821                                                 CodeGenFunction *CGF) {
822   QualType type = Context.getCanonicalType(E->getType());
823 
824   if (type->isIntegerType()) {
825     llvm::APSInt Value(static_cast<uint32_t>(Context.getTypeSize(type)));
826     if (E->isIntegerConstantExpr(Value, Context)) {
827       return llvm::ConstantInt::get(Value);
828     }
829   }
830 
831   llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
832   if (C->getType() == llvm::Type::Int1Ty) {
833     const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
834     C = llvm::ConstantExpr::getZExt(C, BoolTy);
835   }
836   return C;
837 }
838