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Constant.h
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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 
19 namespace 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
41 class Constant : public User {
42  void operator=(const Constant &) LLVM_DELETED_FUNCTION;
44  virtual void anchor();
45 
46 protected:
47  Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
48  : User(ty, vty, Ops, NumOps) {}
49 
50  void destroyConstantImpl();
51 public:
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 
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.
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;
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
void destroyConstantImpl()
Definition: Constants.cpp:212
Constant * getSplatValue() const
Definition: Constants.cpp:1276
unsigned getNumOperands() const
Definition: User.h:108
static bool classof(const Value *V)
Definition: Constant.h:125
const APInt & getUniqueInteger() const
Definition: Constants.cpp:1301
static Constant * getNullValue(Type *Ty)
Definition: Constants.cpp:111
bool isNegativeZeroValue() const
Definition: Constants.cpp:45
#define llvm_unreachable(msg)
Definition: Use.h:60
bool isConstantUsed() const
Definition: Constants.cpp:309
Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
Definition: Constant.h:47
bool canTrap() const
Definition: Constants.cpp:275
LLVM Constant Representation.
Definition: Constant.h:41
bool isZeroValue() const
Return true if the value is negative zero or null value.
Definition: Constants.cpp:66
virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *)
Definition: Constant.h:140
unsigned getValueID() const
Definition: Value.h:233
Constant * getAggregateElement(unsigned Elt) const
Definition: Constants.cpp:183
static Constant * getAllOnesValue(Type *Ty)
Get the all ones value.
Definition: Constants.cpp:163
static Constant * getIntegerValue(Type *Ty, const APInt &V)
Definition: Constants.cpp:146
PossibleRelocationsTy getRelocationInfo() const
Definition: Constants.cpp:337
bool isNullValue() const
Definition: Constants.cpp:75
bool isAllOnesValue() const
Definition: Constants.cpp:88
#define LLVM_DELETED_FUNCTION
Definition: Compiler.h:137
Class for arbitrary precision integers.
Definition: APInt.h:75
virtual void destroyConstant()
Definition: Constant.h:122
void removeDeadConstantUsers() const
Definition: Constants.cpp:395
LLVM Value Representation.
Definition: Value.h:66
bool isThreadDependent() const
isThreadDependent - Return true if the value can vary between threads.
Definition: Constants.cpp:281