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 &) = delete;
43  Constant(const Constant &) = delete;
44  void anchor() override;
45
46protected:
47  Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
48    : User(ty, vty, Ops, NumOps) {}
49
50public:
51  /// Return true if this is the value that would be returned by getNullValue.
52  bool isNullValue() const;
53
54  /// Returns true if the value is one.
55  bool isOneValue() const;
56
57  /// Return true if this is the value that would be returned by
58  /// getAllOnesValue.
59  bool isAllOnesValue() const;
60
61  /// Return true if the value is what would be returned by
62  /// getZeroValueForNegation.
63  bool isNegativeZeroValue() const;
64
65  /// Return true if the value is negative zero or null value.
66  bool isZeroValue() const;
67
68  /// Return true if the value is not the smallest signed value.
69  bool isNotMinSignedValue() const;
70
71  /// Return true if the value is the smallest signed value.
72  bool isMinSignedValue() const;
73
74  /// Return true if evaluation of this constant could trap. This is true for
75  /// things like constant expressions that could divide by zero.
76  bool canTrap() const;
77
78  /// Return true if the value can vary between threads.
79  bool isThreadDependent() const;
80
81  /// Return true if the value is dependent on a dllimport variable.
82  bool isDLLImportDependent() const;
83
84  /// Return true if the constant has users other than constant expressions and
85  /// other dangling things.
86  bool isConstantUsed() const;
87
88  /// This method classifies the entry according to whether or not it may
89  /// generate a relocation entry.  This must be conservative, so if it might
90  /// codegen to a relocatable entry, it should say so.
91  ///
92  /// FIXME: This really should not be in IR.
93  bool needsRelocation() const;
94
95  /// For aggregates (struct/array/vector) return the constant that corresponds
96  /// to the specified element if possible, or null if not. This can return null
97  /// if the element index is a ConstantExpr, or if 'this' is a constant expr.
98  Constant *getAggregateElement(unsigned Elt) const;
99  Constant *getAggregateElement(Constant *Elt) const;
100
101  /// If this is a splat vector constant, meaning that all of the elements have
102  /// the same value, return that value. Otherwise return 0.
103  Constant *getSplatValue() const;
104
105  /// If C is a constant integer then return its value, otherwise C must be a
106  /// vector of constant integers, all equal, and the common value is returned.
107  const APInt &getUniqueInteger() const;
108
109  /// Called if some element of this constant is no longer valid.
110  /// At this point only other constants may be on the use_list for this
111  /// constant.  Any constants on our Use list must also be destroy'd.  The
112  /// implementation must be sure to remove the constant from the list of
113  /// available cached constants.  Implementations should implement
114  /// destroyConstantImpl to remove constants from any pools/maps they are
115  /// contained it.
116  void destroyConstant();
117
118  //// Methods for support type inquiry through isa, cast, and dyn_cast:
119  static inline bool classof(const Value *V) {
120    return V->getValueID() >= ConstantFirstVal &&
121           V->getValueID() <= ConstantLastVal;
122  }
123
124  /// This method is a special form of User::replaceUsesOfWith
125  /// (which does not work on constants) that does work
126  /// on constants.  Basically this method goes through the trouble of building
127  /// a new constant that is equivalent to the current one, with all uses of
128  /// From replaced with uses of To.  After this construction is completed, all
129  /// of the users of 'this' are replaced to use the new constant, and then
130  /// 'this' is deleted.  In general, you should not call this method, instead,
131  /// use Value::replaceAllUsesWith, which automatically dispatches to this
132  /// method as needed.
133  ///
134  void handleOperandChange(Value *, Value *);
135
136  static Constant *getNullValue(Type* Ty);
137
138  /// @returns the value for an integer or vector of integer constant of the
139  /// given type that has all its bits set to true.
140  /// @brief Get the all ones value
141  static Constant *getAllOnesValue(Type* Ty);
142
143  /// Return the value for an integer or pointer constant, or a vector thereof,
144  /// with the given scalar value.
145  static Constant *getIntegerValue(Type *Ty, const APInt &V);
146
147  /// If there are any dead constant users dangling off of this constant, remove
148  /// them. This method is useful for clients that want to check to see if a
149  /// global is unused, but don't want to deal with potentially dead constants
150  /// hanging off of the globals.
151  void removeDeadConstantUsers() const;
152
153  Constant *stripPointerCasts() {
154    return cast<Constant>(Value::stripPointerCasts());
155  }
156
157  const Constant *stripPointerCasts() const {
158    return const_cast<Constant*>(this)->stripPointerCasts();
159  }
160};
161
162} // End llvm namespace
163
164#endif
165