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
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 &) LLVM_DELETED_FUNCTION;
43  Constant(const Constant &) LLVM_DELETED_FUNCTION;
44  virtual void anchor();
45
46protected:
47  Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
48    : User(ty, vty, Ops, NumOps) {}
49
50  void destroyConstantImpl();
51public:
52  /// isNullValue - Return true if this is the value that would be returned by
53  /// getNullValue.
54  bool isNullValue() const;
55
56  /// isAllOnesValue - Return true if this is the value that would be returned by
57  /// getAllOnesValue.
58  bool isAllOnesValue() const;
59
60  /// isNegativeZeroValue - Return true if the value is what would be returned
61  /// by getZeroValueForNegation.
62  bool isNegativeZeroValue() const;
63
64  /// Return true if the value is negative zero or null value.
65  bool isZeroValue() const;
66
67  /// canTrap - Return true if evaluation of this constant could trap.  This is
68  /// true for things like constant expressions that could divide by zero.
69  bool canTrap() const;
70
71  /// isThreadDependent - Return true if the value can vary between threads.
72  bool isThreadDependent() const;
73
74  /// isConstantUsed - Return true if the constant has users other than constant
75  /// exprs and other dangling things.
76  bool isConstantUsed() const;
77
78  enum PossibleRelocationsTy {
79    NoRelocation = 0,
80    LocalRelocation = 1,
81    GlobalRelocations = 2
82  };
83
84  /// getRelocationInfo - This method classifies the entry according to
85  /// whether or not it may generate a relocation entry.  This must be
86  /// conservative, so if it might codegen to a relocatable entry, it should say
87  /// so.  The return values are:
88  ///
89  ///  NoRelocation: This constant pool entry is guaranteed to never have a
90  ///     relocation applied to it (because it holds a simple constant like
91  ///     '4').
92  ///  LocalRelocation: This entry has relocations, but the entries are
93  ///     guaranteed to be resolvable by the static linker, so the dynamic
94  ///     linker will never see them.
95  ///  GlobalRelocations: This entry may have arbitrary relocations.
96  ///
97  /// FIXME: This really should not be in VMCore.
98  PossibleRelocationsTy getRelocationInfo() const;
99
100  /// getAggregateElement - For aggregates (struct/array/vector) return the
101  /// constant that corresponds to the specified element if possible, or null if
102  /// not.  This can return null if the element index is a ConstantExpr, or if
103  /// 'this' is a constant expr.
104  Constant *getAggregateElement(unsigned Elt) const;
105  Constant *getAggregateElement(Constant *Elt) const;
106
107  /// getSplatValue - If this is a splat vector constant, meaning that all of
108  /// the elements have the same value, return that value. Otherwise return 0.
109  Constant *getSplatValue() const;
110
111  /// If C is a constant integer then return its value, otherwise C must be a
112  /// vector of constant integers, all equal, and the common value is returned.
113  const APInt &getUniqueInteger() const;
114
115  /// destroyConstant - Called if some element of this constant is no longer
116  /// valid.  At this point only other constants may be on the use_list for this
117  /// constant.  Any constants on our Use list must also be destroy'd.  The
118  /// implementation must be sure to remove the constant from the list of
119  /// available cached constants.  Implementations should call
120  /// destroyConstantImpl as the last thing they do, to destroy all users and
121  /// delete this.
122  virtual void destroyConstant() { llvm_unreachable("Not reached!"); }
123
124  //// Methods for support type inquiry through isa, cast, and dyn_cast:
125  static inline bool classof(const Value *V) {
126    return V->getValueID() >= ConstantFirstVal &&
127           V->getValueID() <= ConstantLastVal;
128  }
129
130  /// replaceUsesOfWithOnConstant - This method is a special form of
131  /// User::replaceUsesOfWith (which does not work on constants) that does work
132  /// on constants.  Basically this method goes through the trouble of building
133  /// a new constant that is equivalent to the current one, with all uses of
134  /// From replaced with uses of To.  After this construction is completed, all
135  /// of the users of 'this' are replaced to use the new constant, and then
136  /// 'this' is deleted.  In general, you should not call this method, instead,
137  /// use Value::replaceAllUsesWith, which automatically dispatches to this
138  /// method as needed.
139  ///
140  virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) {
141    // Provide a default implementation for constants (like integers) that
142    // cannot use any other values.  This cannot be called at runtime, but needs
143    // to be here to avoid link errors.
144    assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be "
145           "implemented for all constants that have operands!");
146    llvm_unreachable("Constants that do not have operands cannot be using "
147                     "'From'!");
148  }
149
150  static Constant *getNullValue(Type* Ty);
151
152  /// @returns the value for an integer or vector of integer constant of the
153  /// given type that has all its bits set to true.
154  /// @brief Get the all ones value
155  static Constant *getAllOnesValue(Type* Ty);
156
157  /// getIntegerValue - Return the value for an integer or pointer constant,
158  /// or a vector thereof, with the given scalar value.
159  static Constant *getIntegerValue(Type* Ty, const APInt &V);
160
161  /// removeDeadConstantUsers - If there are any dead constant users dangling
162  /// off of this constant, remove them.  This method is useful for clients
163  /// that want to check to see if a global is unused, but don't want to deal
164  /// with potentially dead constants hanging off of the globals.
165  void removeDeadConstantUsers() const;
166};
167
168} // End llvm namespace
169
170#endif
171