aboutsummaryrefslogtreecommitdiffstats
path: root/include/llvm/Constant.h
blob: 8647299299827d40de948587025f3e9e2624aa1b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
//===-- llvm/Constant.h - Constant class definition -------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the declaration of the Constant class.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CONSTANT_H
#define LLVM_CONSTANT_H

#include "llvm/User.h"

namespace llvm {
  class APInt;

  template<typename T> class SmallVectorImpl;
  class LLVMContext;

/// This is an important base class in LLVM. It provides the common facilities
/// of all constant values in an LLVM program. A constant is a value that is
/// immutable at runtime. Functions are constants because their address is
/// immutable. Same with global variables. 
/// 
/// All constants share the capabilities provided in this class. All constants
/// can have a null value. They can have an operand list. Constants can be
/// simple (integer and floating point values), complex (arrays and structures),
/// or expression based (computations yielding a constant value composed of 
/// only certain operators and other constant values).
/// 
/// Note that Constants are immutable (once created they never change) 
/// and are fully shared by structural equivalence.  This means that two 
/// structurally equivalent constants will always have the same address.  
/// Constants are created on demand as needed and never deleted: thus clients 
/// don't have to worry about the lifetime of the objects.
/// @brief LLVM Constant Representation
class Constant : public User {
  void operator=(const Constant &);     // Do not implement
  Constant(const Constant &);           // Do not implement
  
protected:
  Constant(const Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
    : User(ty, vty, Ops, NumOps) {}

  void destroyConstantImpl();
  
  void setOperand(unsigned i, Value *V) {
    User::setOperand(i, V);
  }
public:
  /// isNullValue - Return true if this is the value that would be returned by
  /// getNullValue.
  virtual bool isNullValue() const = 0;

  /// isNegativeZeroValue - Return true if the value is what would be returned 
  /// by getZeroValueForNegation.
  virtual bool isNegativeZeroValue() const { return isNullValue(); }

  /// canTrap - Return true if evaluation of this constant could trap.  This is
  /// true for things like constant expressions that could divide by zero.
  bool canTrap() const;

  /// isConstantUsed - Return true if the constant has users other than constant
  /// exprs and other dangling things.
  bool isConstantUsed() const;
  
  enum PossibleRelocationsTy {
    NoRelocation = 0,
    LocalRelocation = 1,
    GlobalRelocations = 2
  };
  
  /// getRelocationInfo - This method classifies the entry according to
  /// whether or not it may generate a relocation entry.  This must be
  /// conservative, so if it might codegen to a relocatable entry, it should say
  /// so.  The return values are:
  /// 
  ///  NoRelocation: This constant pool entry is guaranteed to never have a
  ///     relocation applied to it (because it holds a simple constant like
  ///     '4').
  ///  LocalRelocation: This entry has relocations, but the entries are
  ///     guaranteed to be resolvable by the static linker, so the dynamic
  ///     linker will never see them.
  ///  GlobalRelocations: This entry may have arbitrary relocations.
  ///
  /// FIXME: This really should not be in VMCore.
  PossibleRelocationsTy getRelocationInfo() const;
  
  // Specialize get/setOperand for Users as their operands are always
  // constants or BasicBlocks as well.
  User *getOperand(unsigned i) {
    return static_cast<User*>(User::getOperand(i));
  }
  const User *getOperand(unsigned i) const {
    return static_cast<const User*>(User::getOperand(i));
  }
  
  /// getVectorElements - This method, which is only valid on constant of vector
  /// type, returns the elements of the vector in the specified smallvector.
  /// This handles breaking down a vector undef into undef elements, etc.  For
  /// constant exprs and other cases we can't handle, we return an empty vector.
  void getVectorElements(SmallVectorImpl<Constant*> &Elts) const;

  /// destroyConstant - Called if some element of this constant is no longer
  /// valid.  At this point only other constants may be on the use_list for this
  /// constant.  Any constants on our Use list must also be destroy'd.  The
  /// implementation must be sure to remove the constant from the list of
  /// available cached constants.  Implementations should call
  /// destroyConstantImpl as the last thing they do, to destroy all users and
  /// delete this.
  virtual void destroyConstant() { assert(0 && "Not reached!"); }

  //// Methods for support type inquiry through isa, cast, and dyn_cast:
  static inline bool classof(const Constant *) { return true; }
  static inline bool classof(const GlobalValue *) { return true; }
  static inline bool classof(const Value *V) {
    return V->getValueID() >= ConstantFirstVal &&
           V->getValueID() <= ConstantLastVal;
  }

  /// replaceUsesOfWithOnConstant - This method is a special form of
  /// User::replaceUsesOfWith (which does not work on constants) that does work
  /// on constants.  Basically this method goes through the trouble of building
  /// a new constant that is equivalent to the current one, with all uses of
  /// From replaced with uses of To.  After this construction is completed, all
  /// of the users of 'this' are replaced to use the new constant, and then
  /// 'this' is deleted.  In general, you should not call this method, instead,
  /// use Value::replaceAllUsesWith, which automatically dispatches to this
  /// method as needed.
  ///
  virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) {
    // Provide a default implementation for constants (like integers) that
    // cannot use any other values.  This cannot be called at runtime, but needs
    // to be here to avoid link errors.
    assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be "
           "implemented for all constants that have operands!");
    assert(0 && "Constants that do not have operands cannot be using 'From'!");
  }
  
  static Constant* getNullValue(const Type* Ty);
  
  /// @returns the value for an integer constant of the given type that has all
  /// its bits set to true.
  /// @brief Get the all ones value
  static Constant* getAllOnesValue(const Type* Ty);

  /// getIntegerValue - Return the value for an integer or pointer constant,
  /// or a vector thereof, with the given scalar value.
  static Constant* getIntegerValue(const Type* Ty, const APInt &V);
};

} // End llvm namespace

#endif