LLVM  4.0.0
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 #include "llvm/IR/Value.h"
19 #include "llvm/Support/Casting.h"
20 
21 namespace llvm {
22 
23 class APInt;
24 
25 /// This is an important base class in LLVM. It provides the common facilities
26 /// of all constant values in an LLVM program. A constant is a value that is
27 /// immutable at runtime. Functions are constants because their address is
28 /// immutable. Same with global variables.
29 ///
30 /// All constants share the capabilities provided in this class. All constants
31 /// can have a null value. They can have an operand list. Constants can be
32 /// simple (integer and floating point values), complex (arrays and structures),
33 /// or expression based (computations yielding a constant value composed of
34 /// only certain operators and other constant values).
35 ///
36 /// Note that Constants are immutable (once created they never change)
37 /// and are fully shared by structural equivalence. This means that two
38 /// structurally equivalent constants will always have the same address.
39 /// Constants are created on demand as needed and never deleted: thus clients
40 /// don't have to worry about the lifetime of the objects.
41 /// @brief LLVM Constant Representation
42 class Constant : public User {
43  void anchor() override;
44 
45 protected:
46  Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
47  : User(ty, vty, Ops, NumOps) {}
48 
49 public:
50  void operator=(const Constant &) = delete;
51  Constant(const Constant &) = delete;
52 
53  /// Return true if this is the value that would be returned by getNullValue.
54  bool isNullValue() const;
55 
56  /// Returns true if the value is one.
57  bool isOneValue() const;
58 
59  /// Return true if this is the value that would be returned by
60  /// getAllOnesValue.
61  bool isAllOnesValue() const;
62 
63  /// Return true if the value is what would be returned by
64  /// getZeroValueForNegation.
65  bool isNegativeZeroValue() const;
66 
67  /// Return true if the value is negative zero or null value.
68  bool isZeroValue() const;
69 
70  /// Return true if the value is not the smallest signed value.
71  bool isNotMinSignedValue() const;
72 
73  /// Return true if the value is the smallest signed value.
74  bool isMinSignedValue() const;
75 
76  /// Return true if evaluation of this constant could trap. This is true for
77  /// things like constant expressions that could divide by zero.
78  bool canTrap() const;
79 
80  /// Return true if the value can vary between threads.
81  bool isThreadDependent() const;
82 
83  /// Return true if the value is dependent on a dllimport variable.
84  bool isDLLImportDependent() const;
85 
86  /// Return true if the constant has users other than constant expressions and
87  /// other dangling things.
88  bool isConstantUsed() const;
89 
90  /// This method classifies the entry according to whether or not it may
91  /// generate a relocation entry. This must be conservative, so if it might
92  /// codegen to a relocatable entry, it should say so.
93  ///
94  /// FIXME: This really should not be in IR.
95  bool needsRelocation() const;
96 
97  /// For aggregates (struct/array/vector) return the constant that corresponds
98  /// to the specified element if possible, or null if not. This can return null
99  /// if the element index is a ConstantExpr, or if 'this' is a constant expr.
100  Constant *getAggregateElement(unsigned Elt) const;
102 
103  /// If this is a splat vector constant, meaning that all of the elements have
104  /// the same value, return that value. Otherwise return 0.
105  Constant *getSplatValue() const;
106 
107  /// If C is a constant integer then return its value, otherwise C must be a
108  /// vector of constant integers, all equal, and the common value is returned.
109  const APInt &getUniqueInteger() const;
110 
111  /// Called if some element of this constant is no longer valid.
112  /// At this point only other constants may be on the use_list for this
113  /// constant. Any constants on our Use list must also be destroy'd. The
114  /// implementation must be sure to remove the constant from the list of
115  /// available cached constants. Implementations should implement
116  /// destroyConstantImpl to remove constants from any pools/maps they are
117  /// contained it.
118  void destroyConstant();
119 
120  //// Methods for support type inquiry through isa, cast, and dyn_cast:
121  static inline bool classof(const Value *V) {
122  return V->getValueID() >= ConstantFirstVal &&
123  V->getValueID() <= ConstantLastVal;
124  }
125 
126  /// This method is a special form of User::replaceUsesOfWith
127  /// (which does not work on constants) that does work
128  /// on constants. Basically this method goes through the trouble of building
129  /// a new constant that is equivalent to the current one, with all uses of
130  /// From replaced with uses of To. After this construction is completed, all
131  /// of the users of 'this' are replaced to use the new constant, and then
132  /// 'this' is deleted. In general, you should not call this method, instead,
133  /// use Value::replaceAllUsesWith, which automatically dispatches to this
134  /// method as needed.
135  ///
136  void handleOperandChange(Value *, Value *);
137 
138  static Constant *getNullValue(Type* Ty);
139 
140  /// @returns the value for an integer or vector of integer constant of the
141  /// given type that has all its bits set to true.
142  /// @brief Get the all ones value
143  static Constant *getAllOnesValue(Type* Ty);
144 
145  /// Return the value for an integer or pointer constant, or a vector thereof,
146  /// with the given scalar value.
147  static Constant *getIntegerValue(Type *Ty, const APInt &V);
148 
149  /// If there are any dead constant users dangling off of this constant, remove
150  /// them. This method is useful for clients that want to check to see if a
151  /// global is unused, but don't want to deal with potentially dead constants
152  /// hanging off of the globals.
153  void removeDeadConstantUsers() const;
154 
156  return cast<Constant>(Value::stripPointerCasts());
157  }
158 
159  const Constant *stripPointerCasts() const {
160  return const_cast<Constant*>(this)->stripPointerCasts();
161  }
162 };
163 
164 } // end namespace llvm
165 
166 #endif // LLVM_IR_CONSTANT_H
Constant * getSplatValue() const
If this is a splat vector constant, meaning that all of the elements have the same value...
Definition: Constants.cpp:1290
static bool classof(const Value *V)
Definition: Constant.h:121
bool isOneValue() const
Returns true if the value is one.
Definition: Constants.cpp:127
const APInt & getUniqueInteger() const
If C is a constant integer then return its value, otherwise C must be a vector of constant integers...
Definition: Constants.cpp:1311
static Constant * getNullValue(Type *Ty)
Constructor to create a '0' constant of arbitrary type.
Definition: Constants.cpp:195
bool isNegativeZeroValue() const
Return true if the value is what would be returned by getZeroValueForNegation.
Definition: Constants.cpp:44
const Constant * stripPointerCasts() const
Definition: Constant.h:159
A Use represents the edge between a Value definition and its users.
Definition: Use.h:56
bool isDLLImportDependent() const
Return true if the value is dependent on a dllimport variable.
Definition: Constants.cpp:396
bool isConstantUsed() const
Return true if the constant has users other than constant expressions and other dangling things...
Definition: Constants.cpp:403
Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
Definition: Constant.h:46
bool isNotMinSignedValue() const
Return true if the value is not the smallest signed value.
Definition: Constants.cpp:171
Constant * stripPointerCasts()
Definition: Constant.h:155
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:45
bool canTrap() const
Return true if evaluation of this constant could trap.
Definition: Constants.cpp:359
This is an important base class in LLVM.
Definition: Constant.h:42
bool isZeroValue() const
Return true if the value is negative zero or null value.
Definition: Constants.cpp:70
unsigned getValueID() const
Return an ID for the concrete type of this object.
Definition: Value.h:434
bool needsRelocation() const
This method classifies the entry according to whether or not it may generate a relocation entry...
Definition: Constants.cpp:415
Constant * getAggregateElement(unsigned Elt) const
For aggregates (struct/array/vector) return the constant that corresponds to the specified element if...
Definition: Constants.cpp:265
static Constant * getAllOnesValue(Type *Ty)
Get the all ones value.
Definition: Constants.cpp:249
static Constant * getIntegerValue(Type *Ty, const APInt &V)
Return the value for an integer or pointer constant, or a vector thereof, with the given scalar value...
Definition: Constants.cpp:232
Value * stripPointerCasts()
Strip off pointer casts, all-zero GEPs, and aliases.
Definition: Value.cpp:490
bool isNullValue() const
Return true if this is the value that would be returned by getNullValue.
Definition: Constants.cpp:90
ValueTy
Concrete subclass of this.
Definition: Value.h:415
void handleOperandChange(Value *, Value *)
This method is a special form of User::replaceUsesOfWith (which does not work on constants) that does...
Definition: Constants.cpp:2693
bool isAllOnesValue() const
Return true if this is the value that would be returned by getAllOnesValue.
Definition: Constants.cpp:105
Class for arbitrary precision integers.
Definition: APInt.h:77
void destroyConstant()
Called if some element of this constant is no longer valid.
Definition: Constants.cpp:288
void removeDeadConstantUsers() const
If there are any dead constant users dangling off of this constant, remove them.
Definition: Constants.cpp:463
LLVM Value Representation.
Definition: Value.h:71
void operator=(const Constant &)=delete
bool isThreadDependent() const
Return true if the value can vary between threads.
Definition: Constants.cpp:389
bool isMinSignedValue() const
Return true if the value is the smallest signed value.
Definition: Constants.cpp:149