Constant.h revision 7cf12c7efd37dc12c3ed536a3f4c373dddac2b85
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 class LLVMContext; 22 23/// This is an important base class in LLVM. It provides the common facilities 24/// of all constant values in an LLVM program. A constant is a value that is 25/// immutable at runtime. Functions are constants because their address is 26/// immutable. Same with global variables. 27/// 28/// All constants share the capabilities provided in this class. All constants 29/// can have a null value. They can have an operand list. Constants can be 30/// simple (integer and floating point values), complex (arrays and structures), 31/// or expression based (computations yielding a constant value composed of 32/// only certain operators and other constant values). 33/// 34/// Note that Constants are immutable (once created they never change) 35/// and are fully shared by structural equivalence. This means that two 36/// structurally equivalent constants will always have the same address. 37/// Constants are created on demand as needed and never deleted: thus clients 38/// don't have to worry about the lifetime of the objects. 39/// @brief LLVM Constant Representation 40class Constant : public User { 41 void operator=(const Constant &); // Do not implement 42 Constant(const Constant &); // Do not implement 43 44protected: 45 Constant(const Type *ty, ValueTy vty, Use *Ops, unsigned NumOps) 46 : User(ty, vty, Ops, NumOps) {} 47 48 void destroyConstantImpl(); 49public: 50 /// isNullValue - Return true if this is the value that would be returned by 51 /// getNullValue. 52 virtual bool isNullValue() const = 0; 53 54 /// isNegativeZeroValue - Return true if the value is what would be returned 55 /// by getZeroValueForNegation. 56 virtual bool isNegativeZeroValue() const { return isNullValue(); } 57 58 /// canTrap - Return true if evaluation of this constant could trap. This is 59 /// true for things like constant expressions that could divide by zero. 60 bool canTrap() const; 61 62 /// getRelocationInfo - This method classifies the entry according to 63 /// whether or not it may generate a relocation entry. This must be 64 /// conservative, so if it might codegen to a relocatable entry, it should say 65 /// so. The return values are: 66 /// 67 /// 0: This constant pool entry is guaranteed to never have a relocation 68 /// applied to it (because it holds a simple constant like '4'). 69 /// 1: This entry has relocations, but the entries are guaranteed to be 70 /// resolvable by the static linker, so the dynamic linker will never see 71 /// them. 72 /// 2: This entry may have arbitrary relocations. 73 /// 74 /// FIXME: This really should not be in VMCore. 75 unsigned getRelocationInfo() const; 76 77 // Specialize get/setOperand for Constants as their operands are always 78 // constants as well. 79 Constant *getOperand(unsigned i) { 80 return static_cast<Constant*>(User::getOperand(i)); 81 } 82 const Constant *getOperand(unsigned i) const { 83 return static_cast<const Constant*>(User::getOperand(i)); 84 } 85 void setOperand(unsigned i, Constant *C) { 86 User::setOperand(i, C); 87 } 88 89 /// getVectorElements - This method, which is only valid on constant of vector 90 /// type, returns the elements of the vector in the specified smallvector. 91 /// This handles breaking down a vector undef into undef elements, etc. For 92 /// constant exprs and other cases we can't handle, we return an empty vector. 93 void getVectorElements(LLVMContext &Context, 94 SmallVectorImpl<Constant*> &Elts) const; 95 96 /// destroyConstant - Called if some element of this constant is no longer 97 /// valid. At this point only other constants may be on the use_list for this 98 /// constant. Any constants on our Use list must also be destroy'd. The 99 /// implementation must be sure to remove the constant from the list of 100 /// available cached constants. Implementations should call 101 /// destroyConstantImpl as the last thing they do, to destroy all users and 102 /// delete this. 103 virtual void destroyConstant() { assert(0 && "Not reached!"); } 104 105 //// Methods for support type inquiry through isa, cast, and dyn_cast: 106 static inline bool classof(const Constant *) { return true; } 107 static inline bool classof(const GlobalValue *) { return true; } 108 static inline bool classof(const Value *V) { 109 return V->getValueID() >= ConstantFirstVal && 110 V->getValueID() <= ConstantLastVal; 111 } 112 113 /// replaceUsesOfWithOnConstant - This method is a special form of 114 /// User::replaceUsesOfWith (which does not work on constants) that does work 115 /// on constants. Basically this method goes through the trouble of building 116 /// a new constant that is equivalent to the current one, with all uses of 117 /// From replaced with uses of To. After this construction is completed, all 118 /// of the users of 'this' are replaced to use the new constant, and then 119 /// 'this' is deleted. In general, you should not call this method, instead, 120 /// use Value::replaceAllUsesWith, which automatically dispatches to this 121 /// method as needed. 122 /// 123 virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) { 124 // Provide a default implementation for constants (like integers) that 125 // cannot use any other values. This cannot be called at runtime, but needs 126 // to be here to avoid link errors. 127 assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be " 128 "implemented for all constants that have operands!"); 129 assert(0 && "Constants that do not have operands cannot be using 'From'!"); 130 } 131}; 132 133} // End llvm namespace 134 135#endif 136