src/llvm/include/llvm/IR/Constant.h

   1 //===-- llvm/Constant.h - Constant class definition -------------*- 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 // This file contains the declaration of the Constant class.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #ifndef LLVM_IR_CONSTANT_H
  15 #define LLVM_IR_CONSTANT_H
  16
  17 #include "llvm/IR/User.h"
  18
  19 namespace llvm {
  20   class APInt;
  21
  22   template<typename T> class SmallVectorImpl;
  23
  24 /// This is an important base class in LLVM. It provides the common facilities
  25 /// of all constant values in an LLVM program. A constant is a value that is
  26 /// immutable at runtime. Functions are constants because their address is
  27 /// immutable. Same with global variables.
  28 ///
  29 /// All constants share the capabilities provided in this class. All constants
  30 /// can have a null value. They can have an operand list. Constants can be
  31 /// simple (integer and floating point values), complex (arrays and structures),
  32 /// or expression based (computations yielding a constant value composed of
  33 /// only certain operators and other constant values).
  34 ///
  35 /// Note that Constants are immutable (once created they never change)
  36 /// and are fully shared by structural equivalence.  This means that two
  37 /// structurally equivalent constants will always have the same address.
  38 /// Constants are created on demand as needed and never deleted: thus clients
  39 /// don't have to worry about the lifetime of the objects.
  40 /// @brief LLVM Constant Representation
  41 class Constant : public User {
  42   void operator=(const Constant &) LLVM_DELETED_FUNCTION;
  43   Constant(const Constant &) LLVM_DELETED_FUNCTION;
  44   void anchor() override;
  45
  46 protected:
  47   Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
  48     : User(ty, vty, Ops, NumOps) {}
  49
  50   void destroyConstantImpl();
  51   void replaceUsesOfWithOnConstantImpl(Constant *Replacement);
  52
  53 public:
  54   /// isNullValue - Return true if this is the value that would be returned by
  55   /// getNullValue.
  56   bool isNullValue() const;
  57
  58   /// \brief Returns true if the value is one.
  59   bool isOneValue() const;
  60
  61   /// isAllOnesValue - Return true if this is the value that would be returned by
  62   /// getAllOnesValue.
  63   bool isAllOnesValue() const;
  64
  65   /// isNegativeZeroValue - Return true if the value is what would be returned
  66   /// by getZeroValueForNegation.
  67   bool isNegativeZeroValue() const;
  68
  69   /// Return true if the value is negative zero or null value.
  70   bool isZeroValue() const;
  71
  72   /// \brief Return true if the value is not the smallest signed value.
  73   bool isNotMinSignedValue() const;
  74
  75   /// \brief Return true if the value is the smallest signed value.
  76   bool isMinSignedValue() const;
  77
  78   /// canTrap - Return true if evaluation of this constant could trap.  This is
  79   /// true for things like constant expressions that could divide by zero.
  80   bool canTrap() const;
  81
  82   /// isThreadDependent - Return true if the value can vary between threads.
  83   bool isThreadDependent() const;
  84
  85   /// Return true if the value is dependent on a dllimport variable.
  86   bool isDLLImportDependent() const;
  87
  88   /// isConstantUsed - Return true if the constant has users other than constant
  89   /// exprs and other dangling things.
  90   bool isConstantUsed() const;
  91
  92   enum PossibleRelocationsTy {
  93     NoRelocation = 0,
  94     LocalRelocation = 1,
  95     GlobalRelocations = 2
  96   };
  97
  98   /// getRelocationInfo - This method classifies the entry according to
  99   /// whether or not it may generate a relocation entry.  This must be
 100   /// conservative, so if it might codegen to a relocatable entry, it should say
 101   /// so.  The return values are:
 102   ///
 103   ///  NoRelocation: This constant pool entry is guaranteed to never have a
 104   ///     relocation applied to it (because it holds a simple constant like
 105   ///     '4').
 106   ///  LocalRelocation: This entry has relocations, but the entries are
 107   ///     guaranteed to be resolvable by the static linker, so the dynamic
 108   ///     linker will never see them.
 109   ///  GlobalRelocations: This entry may have arbitrary relocations.
 110   ///
 111   /// FIXME: This really should not be in VMCore.
 112   PossibleRelocationsTy getRelocationInfo() const;
 113
 114   /// getAggregateElement - For aggregates (struct/array/vector) return the
 115   /// constant that corresponds to the specified element if possible, or null if
 116   /// not.  This can return null if the element index is a ConstantExpr, or if
 117   /// 'this' is a constant expr.
 118   Constant *getAggregateElement(unsigned Elt) const;
 119   Constant *getAggregateElement(Constant *Elt) const;
 120
 121   /// getSplatValue - If this is a splat vector constant, meaning that all of
 122   /// the elements have the same value, return that value. Otherwise return 0.
 123   Constant *getSplatValue() const;
 124
 125   /// If C is a constant integer then return its value, otherwise C must be a
 126   /// vector of constant integers, all equal, and the common value is returned.
 127   const APInt &getUniqueInteger() const;
 128
 129   /// destroyConstant - Called if some element of this constant is no longer
 130   /// valid.  At this point only other constants may be on the use_list for this
 131   /// constant.  Any constants on our Use list must also be destroy'd.  The
 132   /// implementation must be sure to remove the constant from the list of
 133   /// available cached constants.  Implementations should call
 134   /// destroyConstantImpl as the last thing they do, to destroy all users and
 135   /// delete this.
 136   virtual void destroyConstant() { llvm_unreachable("Not reached!"); }
 137
 138   //// Methods for support type inquiry through isa, cast, and dyn_cast:
 139   static inline bool classof(const Value *V) {
 140     return V->getValueID() >= ConstantFirstVal &&
 141            V->getValueID() <= ConstantLastVal;
 142   }
 143
 144   /// replaceUsesOfWithOnConstant - This method is a special form of
 145   /// User::replaceUsesOfWith (which does not work on constants) that does work
 146   /// on constants.  Basically this method goes through the trouble of building
 147   /// a new constant that is equivalent to the current one, with all uses of
 148   /// From replaced with uses of To.  After this construction is completed, all
 149   /// of the users of 'this' are replaced to use the new constant, and then
 150   /// 'this' is deleted.  In general, you should not call this method, instead,
 151   /// use Value::replaceAllUsesWith, which automatically dispatches to this
 152   /// method as needed.
 153   ///
 154   virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) {
 155     // Provide a default implementation for constants (like integers) that
 156     // cannot use any other values.  This cannot be called at runtime, but needs
 157     // to be here to avoid link errors.
 158     assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be "
 159            "implemented for all constants that have operands!");
 160     llvm_unreachable("Constants that do not have operands cannot be using "
 161                      "'From'!");
 162   }
 163
 164   static Constant *getNullValue(Type* Ty);
 165
 166   /// @returns the value for an integer or vector of integer constant of the
 167   /// given type that has all its bits set to true.
 168   /// @brief Get the all ones value
 169   static Constant *getAllOnesValue(Type* Ty);
 170
 171   /// getIntegerValue - Return the value for an integer or pointer constant,
 172   /// or a vector thereof, with the given scalar value.
 173   static Constant *getIntegerValue(Type* Ty, const APInt &V);
 174
 175   /// removeDeadConstantUsers - If there are any dead constant users dangling
 176   /// off of this constant, remove them.  This method is useful for clients
 177   /// that want to check to see if a global is unused, but don't want to deal
 178   /// with potentially dead constants hanging off of the globals.
 179   void removeDeadConstantUsers() const;
 180
 181   Constant *stripPointerCasts() {
 182     return cast<Constant>(Value::stripPointerCasts());
 183   }
 184
 185   const Constant *stripPointerCasts() const {
 186     return const_cast<Constant*>(this)->stripPointerCasts();
 187   }
 188 };
 189
 190 } // End llvm namespace
 191
 192 #endif