Constant.h revision 4c7c0f23533565c7e2ddf71e01bf50f2aede5f1b 
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  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
41class Constant : public User {
42  void operator=(const Constant &);     // Do not implement
43  Constant(const Constant &);           // Do not implement
44
45protected:
46  Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
47    : User(ty, vty, Ops, NumOps) {}
48
49  void destroyConstantImpl();
50public:
51  /// isNullValue - Return true if this is the value that would be returned by
52  /// getNullValue.
53  bool isNullValue() const;
54
55  /// isAllOnesValue - Return true if this is the value that would be returned by
56  /// getAllOnesValue.
57  bool isAllOnesValue() const;
58
59  /// isNegativeZeroValue - Return true if the value is what would be returned
60  /// by getZeroValueForNegation.
61  bool isNegativeZeroValue() const;
62
63  /// canTrap - Return true if evaluation of this constant could trap.  This is
64  /// true for things like constant expressions that could divide by zero.
65  bool canTrap() const;
66
67  /// isConstantUsed - Return true if the constant has users other than constant
68  /// exprs and other dangling things.
69  bool isConstantUsed() const;
70
71  enum PossibleRelocationsTy {
72    NoRelocation = 0,
73    LocalRelocation = 1,
74    GlobalRelocations = 2
75  };
76
77  /// getRelocationInfo - This method classifies the entry according to
78  /// whether or not it may generate a relocation entry.  This must be
79  /// conservative, so if it might codegen to a relocatable entry, it should say
80  /// so.  The return values are:
81  ///
82  ///  NoRelocation: This constant pool entry is guaranteed to never have a
83  ///     relocation applied to it (because it holds a simple constant like
84  ///     '4').
85  ///  LocalRelocation: This entry has relocations, but the entries are
86  ///     guaranteed to be resolvable by the static linker, so the dynamic
87  ///     linker will never see them.
88  ///  GlobalRelocations: This entry may have arbitrary relocations.
89  ///
90  /// FIXME: This really should not be in VMCore.
91  PossibleRelocationsTy getRelocationInfo() const;
92
93  /// getVectorElements - This method, which is only valid on constant of vector
94  /// type, returns the elements of the vector in the specified smallvector.
95  /// This handles breaking down a vector undef into undef elements, etc.  For
96  /// constant exprs and other cases we can't handle, we return an empty vector.
97  void getVectorElements(SmallVectorImpl<Constant*> &Elts) const;
98
99  /// destroyConstant - Called if some element of this constant is no longer
100  /// valid.  At this point only other constants may be on the use_list for this
101  /// constant.  Any constants on our Use list must also be destroy'd.  The
102  /// implementation must be sure to remove the constant from the list of
103  /// available cached constants.  Implementations should call
104  /// destroyConstantImpl as the last thing they do, to destroy all users and
105  /// delete this.
106  virtual void destroyConstant() { assert(0 && "Not reached!"); }
107
108  //// Methods for support type inquiry through isa, cast, and dyn_cast:
109  static inline bool classof(const Constant *) { return true; }
110  static inline bool classof(const GlobalValue *) { return true; }
111  static inline bool classof(const Value *V) {
112    return V->getValueID() >= ConstantFirstVal &&
113           V->getValueID() <= ConstantLastVal;
114  }
115
116  /// replaceUsesOfWithOnConstant - This method is a special form of
117  /// User::replaceUsesOfWith (which does not work on constants) that does work
118  /// on constants.  Basically this method goes through the trouble of building
119  /// a new constant that is equivalent to the current one, with all uses of
120  /// From replaced with uses of To.  After this construction is completed, all
121  /// of the users of 'this' are replaced to use the new constant, and then
122  /// 'this' is deleted.  In general, you should not call this method, instead,
123  /// use Value::replaceAllUsesWith, which automatically dispatches to this
124  /// method as needed.
125  ///
126  virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) {
127    // Provide a default implementation for constants (like integers) that
128    // cannot use any other values.  This cannot be called at runtime, but needs
129    // to be here to avoid link errors.
130    assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be "
131           "implemented for all constants that have operands!");
132    assert(0 && "Constants that do not have operands cannot be using 'From'!");
133  }
134
135  static Constant *getNullValue(Type* Ty);
136
137  /// @returns the value for an integer constant of the given type that has all
138  /// its bits set to true.
139  /// @brief Get the all ones value
140  static Constant *getAllOnesValue(Type* Ty);
141
142  /// getIntegerValue - Return the value for an integer or pointer constant,
143  /// or a vector thereof, with the given scalar value.
144  static Constant *getIntegerValue(Type* Ty, const APInt &V);
145
146  /// removeDeadConstantUsers - If there are any dead constant users dangling
147  /// off of this constant, remove them.  This method is useful for clients
148  /// that want to check to see if a global is unused, but don't want to deal
149  /// with potentially dead constants hanging off of the globals.
150  void removeDeadConstantUsers() const;
151};
152
153} // End llvm namespace
154
155#endif
156