Constant.h revision db2323148b959ffcaf7a3498f94de5fa6d3e6eb7
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_CONSTANT_H 15#define LLVM_CONSTANT_H 16 17#include "llvm/User.h" 18 19namespace llvm { 20 template<typename T> class SmallVectorImpl; 21 22 namespace Reloc { 23 const unsigned None = 0; 24 const unsigned Local = 1 << 0; ///< Local relocations are required 25 const unsigned Global = 1 << 1; ///< Global relocations are required 26 const unsigned LocalOrGlobal = Local | Global; 27 } 28 29/// This is an important base class in LLVM. It provides the common facilities 30/// of all constant values in an LLVM program. A constant is a value that is 31/// immutable at runtime. Functions are constants because their address is 32/// immutable. Same with global variables. 33/// 34/// All constants share the capabilities provided in this class. All constants 35/// can have a null value. They can have an operand list. Constants can be 36/// simple (integer and floating point values), complex (arrays and structures), 37/// or expression based (computations yielding a constant value composed of 38/// only certain operators and other constant values). 39/// 40/// Note that Constants are immutable (once created they never change) 41/// and are fully shared by structural equivalence. This means that two 42/// structurally equivalent constants will always have the same address. 43/// Constants are created on demand as needed and never deleted: thus clients 44/// don't have to worry about the lifetime of the objects. 45/// @brief LLVM Constant Representation 46class Constant : public User { 47 void operator=(const Constant &); // Do not implement 48 Constant(const Constant &); // Do not implement 49protected: 50 Constant(const Type *ty, ValueTy vty, Use *Ops, unsigned NumOps) 51 : User(ty, vty, Ops, NumOps) {} 52 53 void destroyConstantImpl(); 54public: 55 /// Static constructor to get a '0' constant of arbitrary type... 56 /// 57 static Constant *getNullValue(const Type *Ty); 58 59 /// Static constructor to get a '-1' constant. This supports integers and 60 /// vectors. 61 /// 62 static Constant *getAllOnesValue(const Type *Ty); 63 64 /// isNullValue - Return true if this is the value that would be returned by 65 /// getNullValue. 66 virtual bool isNullValue() const = 0; 67 68 /// canTrap - Return true if evaluation of this constant could trap. This is 69 /// true for things like constant expressions that could divide by zero. 70 bool canTrap() const; 71 72 /// ContainsRelocations - Return true if the constant value contains 73 /// relocations which cannot be resolved at compile time. 74 bool ContainsRelocations(unsigned Kind = Reloc::LocalOrGlobal) const; 75 76 // Specialize get/setOperand for Constants as their operands are always 77 // constants as well. 78 Constant *getOperand(unsigned i) { 79 return static_cast<Constant*>(User::getOperand(i)); 80 } 81 const Constant *getOperand(unsigned i) const { 82 return static_cast<const Constant*>(User::getOperand(i)); 83 } 84 void setOperand(unsigned i, Constant *C) { 85 User::setOperand(i, C); 86 } 87 88 /// getVectorElements - This method, which is only valid on constant of vector 89 /// type, returns the elements of the vector in the specified smallvector. 90 /// This handles breaking down a vector undef into undef elements, etc. For 91 /// constant exprs and other cases we can't handle, we return an empty vector. 92 void getVectorElements(SmallVectorImpl<Constant*> &Elts) const; 93 94 /// destroyConstant - Called if some element of this constant is no longer 95 /// valid. At this point only other constants may be on the use_list for this 96 /// constant. Any constants on our Use list must also be destroy'd. The 97 /// implementation must be sure to remove the constant from the list of 98 /// available cached constants. Implementations should call 99 /// destroyConstantImpl as the last thing they do, to destroy all users and 100 /// delete this. 101 virtual void destroyConstant() { assert(0 && "Not reached!"); } 102 103 //// Methods for support type inquiry through isa, cast, and dyn_cast: 104 static inline bool classof(const Constant *) { return true; } 105 static inline bool classof(const GlobalValue *) { return true; } 106 static inline bool classof(const Value *V) { 107 return V->getValueID() >= ConstantFirstVal && 108 V->getValueID() <= ConstantLastVal; 109 } 110 111 /// replaceUsesOfWithOnConstant - This method is a special form of 112 /// User::replaceUsesOfWith (which does not work on constants) that does work 113 /// on constants. Basically this method goes through the trouble of building 114 /// a new constant that is equivalent to the current one, with all uses of 115 /// From replaced with uses of To. After this construction is completed, all 116 /// of the users of 'this' are replaced to use the new constant, and then 117 /// 'this' is deleted. In general, you should not call this method, instead, 118 /// use Value::replaceAllUsesWith, which automatically dispatches to this 119 /// method as needed. 120 /// 121 virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) { 122 // Provide a default implementation for constants (like integers) that 123 // cannot use any other values. This cannot be called at runtime, but needs 124 // to be here to avoid link errors. 125 assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be " 126 "implemented for all constants that have operands!"); 127 assert(0 && "Constants that do not have operands cannot be using 'From'!"); 128 } 129}; 130 131} // End llvm namespace 132 133#endif 134