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      1 //===-- CGValue.h - LLVM CodeGen wrappers for llvm::Value* ------*- C++ -*-===//
      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 // These classes implement wrappers around llvm::Value in order to
     11 // fully represent the range of values for C L- and R- values.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #ifndef CLANG_CODEGEN_CGVALUE_H
     16 #define CLANG_CODEGEN_CGVALUE_H
     17 
     18 #include "clang/AST/ASTContext.h"
     19 #include "clang/AST/Type.h"
     20 
     21 namespace llvm {
     22   class Constant;
     23   class Value;
     24 }
     25 
     26 namespace clang {
     27   class ObjCPropertyRefExpr;
     28 
     29 namespace CodeGen {
     30   class CGBitFieldInfo;
     31 
     32 /// RValue - This trivial value class is used to represent the result of an
     33 /// expression that is evaluated.  It can be one of three things: either a
     34 /// simple LLVM SSA value, a pair of SSA values for complex numbers, or the
     35 /// address of an aggregate value in memory.
     36 class RValue {
     37   enum Flavor { Scalar, Complex, Aggregate };
     38 
     39   // Stores first value and flavor.
     40   llvm::PointerIntPair<llvm::Value *, 2, Flavor> V1;
     41   // Stores second value and volatility.
     42   llvm::PointerIntPair<llvm::Value *, 1, bool> V2;
     43 
     44 public:
     45   bool isScalar() const { return V1.getInt() == Scalar; }
     46   bool isComplex() const { return V1.getInt() == Complex; }
     47   bool isAggregate() const { return V1.getInt() == Aggregate; }
     48 
     49   bool isVolatileQualified() const { return V2.getInt(); }
     50 
     51   /// getScalarVal() - Return the Value* of this scalar value.
     52   llvm::Value *getScalarVal() const {
     53     assert(isScalar() && "Not a scalar!");
     54     return V1.getPointer();
     55   }
     56 
     57   /// getComplexVal - Return the real/imag components of this complex value.
     58   ///
     59   std::pair<llvm::Value *, llvm::Value *> getComplexVal() const {
     60     return std::make_pair(V1.getPointer(), V2.getPointer());
     61   }
     62 
     63   /// getAggregateAddr() - Return the Value* of the address of the aggregate.
     64   llvm::Value *getAggregateAddr() const {
     65     assert(isAggregate() && "Not an aggregate!");
     66     return V1.getPointer();
     67   }
     68 
     69   static RValue get(llvm::Value *V) {
     70     RValue ER;
     71     ER.V1.setPointer(V);
     72     ER.V1.setInt(Scalar);
     73     ER.V2.setInt(false);
     74     return ER;
     75   }
     76   static RValue getComplex(llvm::Value *V1, llvm::Value *V2) {
     77     RValue ER;
     78     ER.V1.setPointer(V1);
     79     ER.V2.setPointer(V2);
     80     ER.V1.setInt(Complex);
     81     ER.V2.setInt(false);
     82     return ER;
     83   }
     84   static RValue getComplex(const std::pair<llvm::Value *, llvm::Value *> &C) {
     85     return getComplex(C.first, C.second);
     86   }
     87   // FIXME: Aggregate rvalues need to retain information about whether they are
     88   // volatile or not.  Remove default to find all places that probably get this
     89   // wrong.
     90   static RValue getAggregate(llvm::Value *V, bool Volatile = false) {
     91     RValue ER;
     92     ER.V1.setPointer(V);
     93     ER.V1.setInt(Aggregate);
     94     ER.V2.setInt(Volatile);
     95     return ER;
     96   }
     97 };
     98 
     99 
    100 /// LValue - This represents an lvalue references.  Because C/C++ allow
    101 /// bitfields, this is not a simple LLVM pointer, it may be a pointer plus a
    102 /// bitrange.
    103 class LValue {
    104   enum {
    105     Simple,       // This is a normal l-value, use getAddress().
    106     VectorElt,    // This is a vector element l-value (V[i]), use getVector*
    107     BitField,     // This is a bitfield l-value, use getBitfield*.
    108     ExtVectorElt, // This is an extended vector subset, use getExtVectorComp
    109     PropertyRef   // This is an Objective-C property reference, use
    110                   // getPropertyRefExpr
    111   } LVType;
    112 
    113   llvm::Value *V;
    114 
    115   union {
    116     // Index into a vector subscript: V[i]
    117     llvm::Value *VectorIdx;
    118 
    119     // ExtVector element subset: V.xyx
    120     llvm::Constant *VectorElts;
    121 
    122     // BitField start bit and size
    123     const CGBitFieldInfo *BitFieldInfo;
    124 
    125     // Obj-C property reference expression
    126     const ObjCPropertyRefExpr *PropertyRefExpr;
    127   };
    128 
    129   QualType Type;
    130 
    131   // 'const' is unused here
    132   Qualifiers Quals;
    133 
    134   /// The alignment to use when accessing this lvalue.
    135   unsigned short Alignment;
    136 
    137   // objective-c's ivar
    138   bool Ivar:1;
    139 
    140   // objective-c's ivar is an array
    141   bool ObjIsArray:1;
    142 
    143   // LValue is non-gc'able for any reason, including being a parameter or local
    144   // variable.
    145   bool NonGC: 1;
    146 
    147   // Lvalue is a global reference of an objective-c object
    148   bool GlobalObjCRef : 1;
    149 
    150   // Lvalue is a thread local reference
    151   bool ThreadLocalRef : 1;
    152 
    153   Expr *BaseIvarExp;
    154 
    155   /// TBAAInfo - TBAA information to attach to dereferences of this LValue.
    156   llvm::MDNode *TBAAInfo;
    157 
    158 private:
    159   void Initialize(QualType Type, Qualifiers Quals, unsigned Alignment = 0,
    160                   llvm::MDNode *TBAAInfo = 0) {
    161     this->Type = Type;
    162     this->Quals = Quals;
    163     this->Alignment = Alignment;
    164     assert(this->Alignment == Alignment && "Alignment exceeds allowed max!");
    165 
    166     // Initialize Objective-C flags.
    167     this->Ivar = this->ObjIsArray = this->NonGC = this->GlobalObjCRef = false;
    168     this->ThreadLocalRef = false;
    169     this->BaseIvarExp = 0;
    170     this->TBAAInfo = TBAAInfo;
    171   }
    172 
    173 public:
    174   bool isSimple() const { return LVType == Simple; }
    175   bool isVectorElt() const { return LVType == VectorElt; }
    176   bool isBitField() const { return LVType == BitField; }
    177   bool isExtVectorElt() const { return LVType == ExtVectorElt; }
    178   bool isPropertyRef() const { return LVType == PropertyRef; }
    179 
    180   bool isVolatileQualified() const { return Quals.hasVolatile(); }
    181   bool isRestrictQualified() const { return Quals.hasRestrict(); }
    182   unsigned getVRQualifiers() const {
    183     return Quals.getCVRQualifiers() & ~Qualifiers::Const;
    184   }
    185 
    186   QualType getType() const { return Type; }
    187 
    188   Qualifiers::ObjCLifetime getObjCLifetime() const {
    189     return Quals.getObjCLifetime();
    190   }
    191 
    192   bool isObjCIvar() const { return Ivar; }
    193   void setObjCIvar(bool Value) { Ivar = Value; }
    194 
    195   bool isObjCArray() const { return ObjIsArray; }
    196   void setObjCArray(bool Value) { ObjIsArray = Value; }
    197 
    198   bool isNonGC () const { return NonGC; }
    199   void setNonGC(bool Value) { NonGC = Value; }
    200 
    201   bool isGlobalObjCRef() const { return GlobalObjCRef; }
    202   void setGlobalObjCRef(bool Value) { GlobalObjCRef = Value; }
    203 
    204   bool isThreadLocalRef() const { return ThreadLocalRef; }
    205   void setThreadLocalRef(bool Value) { ThreadLocalRef = Value;}
    206 
    207   bool isObjCWeak() const {
    208     return Quals.getObjCGCAttr() == Qualifiers::Weak;
    209   }
    210   bool isObjCStrong() const {
    211     return Quals.getObjCGCAttr() == Qualifiers::Strong;
    212   }
    213 
    214   bool isVolatile() const {
    215     return Quals.hasVolatile();
    216   }
    217 
    218   Expr *getBaseIvarExp() const { return BaseIvarExp; }
    219   void setBaseIvarExp(Expr *V) { BaseIvarExp = V; }
    220 
    221   llvm::MDNode *getTBAAInfo() const { return TBAAInfo; }
    222   void setTBAAInfo(llvm::MDNode *N) { TBAAInfo = N; }
    223 
    224   const Qualifiers &getQuals() const { return Quals; }
    225   Qualifiers &getQuals() { return Quals; }
    226 
    227   unsigned getAddressSpace() const { return Quals.getAddressSpace(); }
    228 
    229   unsigned getAlignment() const { return Alignment; }
    230 
    231   // simple lvalue
    232   llvm::Value *getAddress() const { assert(isSimple()); return V; }
    233   void setAddress(llvm::Value *address) {
    234     assert(isSimple());
    235     V = address;
    236   }
    237 
    238   // vector elt lvalue
    239   llvm::Value *getVectorAddr() const { assert(isVectorElt()); return V; }
    240   llvm::Value *getVectorIdx() const { assert(isVectorElt()); return VectorIdx; }
    241 
    242   // extended vector elements.
    243   llvm::Value *getExtVectorAddr() const { assert(isExtVectorElt()); return V; }
    244   llvm::Constant *getExtVectorElts() const {
    245     assert(isExtVectorElt());
    246     return VectorElts;
    247   }
    248 
    249   // bitfield lvalue
    250   llvm::Value *getBitFieldBaseAddr() const {
    251     assert(isBitField());
    252     return V;
    253   }
    254   const CGBitFieldInfo &getBitFieldInfo() const {
    255     assert(isBitField());
    256     return *BitFieldInfo;
    257   }
    258 
    259   // property ref lvalue
    260   llvm::Value *getPropertyRefBaseAddr() const {
    261     assert(isPropertyRef());
    262     return V;
    263   }
    264   const ObjCPropertyRefExpr *getPropertyRefExpr() const {
    265     assert(isPropertyRef());
    266     return PropertyRefExpr;
    267   }
    268 
    269   static LValue MakeAddr(llvm::Value *address, QualType type,
    270                          unsigned alignment, ASTContext &Context,
    271                          llvm::MDNode *TBAAInfo = 0) {
    272     Qualifiers qs = type.getQualifiers();
    273     qs.setObjCGCAttr(Context.getObjCGCAttrKind(type));
    274 
    275     LValue R;
    276     R.LVType = Simple;
    277     R.V = address;
    278     R.Initialize(type, qs, alignment, TBAAInfo);
    279     return R;
    280   }
    281 
    282   static LValue MakeVectorElt(llvm::Value *Vec, llvm::Value *Idx,
    283                               QualType type) {
    284     LValue R;
    285     R.LVType = VectorElt;
    286     R.V = Vec;
    287     R.VectorIdx = Idx;
    288     R.Initialize(type, type.getQualifiers());
    289     return R;
    290   }
    291 
    292   static LValue MakeExtVectorElt(llvm::Value *Vec, llvm::Constant *Elts,
    293                                  QualType type) {
    294     LValue R;
    295     R.LVType = ExtVectorElt;
    296     R.V = Vec;
    297     R.VectorElts = Elts;
    298     R.Initialize(type, type.getQualifiers());
    299     return R;
    300   }
    301 
    302   /// \brief Create a new object to represent a bit-field access.
    303   ///
    304   /// \param BaseValue - The base address of the structure containing the
    305   /// bit-field.
    306   /// \param Info - The information describing how to perform the bit-field
    307   /// access.
    308   static LValue MakeBitfield(llvm::Value *BaseValue,
    309                              const CGBitFieldInfo &Info,
    310                              QualType type) {
    311     LValue R;
    312     R.LVType = BitField;
    313     R.V = BaseValue;
    314     R.BitFieldInfo = &Info;
    315     R.Initialize(type, type.getQualifiers());
    316     return R;
    317   }
    318 
    319   // FIXME: It is probably bad that we aren't emitting the target when we build
    320   // the lvalue. However, this complicates the code a bit, and I haven't figured
    321   // out how to make it go wrong yet.
    322   static LValue MakePropertyRef(const ObjCPropertyRefExpr *E,
    323                                 llvm::Value *Base) {
    324     LValue R;
    325     R.LVType = PropertyRef;
    326     R.V = Base;
    327     R.PropertyRefExpr = E;
    328     R.Initialize(QualType(), Qualifiers());
    329     return R;
    330   }
    331 };
    332 
    333 /// An aggregate value slot.
    334 class AggValueSlot {
    335   /// The address.
    336   llvm::Value *Addr;
    337 
    338   // Qualifiers
    339   Qualifiers Quals;
    340 
    341   /// DestructedFlag - This is set to true if some external code is
    342   /// responsible for setting up a destructor for the slot.  Otherwise
    343   /// the code which constructs it should push the appropriate cleanup.
    344   bool DestructedFlag : 1;
    345 
    346   /// ObjCGCFlag - This is set to true if writing to the memory in the
    347   /// slot might require calling an appropriate Objective-C GC
    348   /// barrier.  The exact interaction here is unnecessarily mysterious.
    349   bool ObjCGCFlag : 1;
    350 
    351   /// ZeroedFlag - This is set to true if the memory in the slot is
    352   /// known to be zero before the assignment into it.  This means that
    353   /// zero fields don't need to be set.
    354   bool ZeroedFlag : 1;
    355 
    356   /// AliasedFlag - This is set to true if the slot might be aliased
    357   /// and it's not undefined behavior to access it through such an
    358   /// alias.  Note that it's always undefined behavior to access a C++
    359   /// object that's under construction through an alias derived from
    360   /// outside the construction process.
    361   ///
    362   /// This flag controls whether calls that produce the aggregate
    363   /// value may be evaluated directly into the slot, or whether they
    364   /// must be evaluated into an unaliased temporary and then memcpy'ed
    365   /// over.  Since it's invalid in general to memcpy a non-POD C++
    366   /// object, it's important that this flag never be set when
    367   /// evaluating an expression which constructs such an object.
    368   bool AliasedFlag : 1;
    369 
    370 public:
    371   enum IsAliased_t { IsNotAliased, IsAliased };
    372   enum IsDestructed_t { IsNotDestructed, IsDestructed };
    373   enum IsZeroed_t { IsNotZeroed, IsZeroed };
    374   enum NeedsGCBarriers_t { DoesNotNeedGCBarriers, NeedsGCBarriers };
    375 
    376   /// ignored - Returns an aggregate value slot indicating that the
    377   /// aggregate value is being ignored.
    378   static AggValueSlot ignored() {
    379     AggValueSlot AV;
    380     AV.Addr = 0;
    381     AV.Quals = Qualifiers();
    382     AV.DestructedFlag = AV.ObjCGCFlag = AV.ZeroedFlag = AV.AliasedFlag = false;
    383     return AV;
    384   }
    385 
    386   /// forAddr - Make a slot for an aggregate value.
    387   ///
    388   /// \param quals - The qualifiers that dictate how the slot should
    389   /// be initialied. Only 'volatile' and the Objective-C lifetime
    390   /// qualifiers matter.
    391   ///
    392   /// \param isDestructed - true if something else is responsible
    393   ///   for calling destructors on this object
    394   /// \param needsGC - true if the slot is potentially located
    395   ///   somewhere that ObjC GC calls should be emitted for
    396   static AggValueSlot forAddr(llvm::Value *addr, Qualifiers quals,
    397                               IsDestructed_t isDestructed,
    398                               NeedsGCBarriers_t needsGC,
    399                               IsAliased_t isAliased,
    400                               IsZeroed_t isZeroed = IsNotZeroed) {
    401     AggValueSlot AV;
    402     AV.Addr = addr;
    403     AV.Quals = quals;
    404     AV.DestructedFlag = isDestructed;
    405     AV.ObjCGCFlag = needsGC;
    406     AV.ZeroedFlag = isZeroed;
    407     AV.AliasedFlag = isAliased;
    408     return AV;
    409   }
    410 
    411   static AggValueSlot forLValue(LValue LV, IsDestructed_t isDestructed,
    412                                 NeedsGCBarriers_t needsGC,
    413                                 IsAliased_t isAliased,
    414                                 IsZeroed_t isZeroed = IsNotZeroed) {
    415     return forAddr(LV.getAddress(), LV.getQuals(),
    416                    isDestructed, needsGC, isAliased, isZeroed);
    417   }
    418 
    419   IsDestructed_t isExternallyDestructed() const {
    420     return IsDestructed_t(DestructedFlag);
    421   }
    422   void setExternallyDestructed(bool destructed = true) {
    423     DestructedFlag = destructed;
    424   }
    425 
    426   Qualifiers getQualifiers() const { return Quals; }
    427 
    428   bool isVolatile() const {
    429     return Quals.hasVolatile();
    430   }
    431 
    432   Qualifiers::ObjCLifetime getObjCLifetime() const {
    433     return Quals.getObjCLifetime();
    434   }
    435 
    436   NeedsGCBarriers_t requiresGCollection() const {
    437     return NeedsGCBarriers_t(ObjCGCFlag);
    438   }
    439 
    440   llvm::Value *getAddr() const {
    441     return Addr;
    442   }
    443 
    444   bool isIgnored() const {
    445     return Addr == 0;
    446   }
    447 
    448   IsAliased_t isPotentiallyAliased() const {
    449     return IsAliased_t(AliasedFlag);
    450   }
    451 
    452   RValue asRValue() const {
    453     return RValue::getAggregate(getAddr(), isVolatile());
    454   }
    455 
    456   void setZeroed(bool V = true) { ZeroedFlag = V; }
    457   IsZeroed_t isZeroed() const {
    458     return IsZeroed_t(ZeroedFlag);
    459   }
    460 };
    461 
    462 }  // end namespace CodeGen
    463 }  // end namespace clang
    464 
    465 #endif
    466