LLVM  6.0.0svn
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 protected:
44  Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
45  : User(ty, vty, Ops, NumOps) {}
46 
47 public:
48  void operator=(const Constant &) = delete;
49  Constant(const Constant &) = delete;
50 
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;
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 bool classof(const Value *V) {
120  static_assert(ConstantFirstVal == 0, "V->getValueID() >= ConstantFirstVal always succeeds");
121  return 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  const Constant *stripPointerCasts() const {
154  return cast<Constant>(Value::stripPointerCasts());
155  }
156 
158  return const_cast<Constant*>(
159  static_cast<const Constant *>(this)->stripPointerCasts());
160  }
161 };
162 
163 } // end namespace llvm
164 
165 #endif // LLVM_IR_CONSTANT_H
bool isAllOnesValue() const
Return true if this is the value that would be returned by getAllOnesValue.
Definition: Constants.cpp:101
unsigned getValueID() const
Return an ID for the concrete type of this object.
Definition: Value.h:465
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
bool needsRelocation() const
This method classifies the entry according to whether or not it may generate a relocation entry...
Definition: Constants.cpp:427
bool isConstantUsed() const
Return true if the constant has users other than constant expressions and other dangling things...
Definition: Constants.cpp:415
static bool classof(const Value *V)
Definition: Constant.h:119
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:1294
static Constant * getNullValue(Type *Ty)
Constructor to create a &#39;0&#39; constant of arbitrary type.
Definition: Constants.cpp:207
A Use represents the edge between a Value definition and its users.
Definition: Use.h:56
bool isNullValue() const
Return true if this is the value that would be returned by getNullValue.
Definition: Constants.cpp:86
bool canTrap() const
Return true if evaluation of this constant could trap.
Definition: Constants.cpp:371
Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
Definition: Constant.h:44
bool isMinSignedValue() const
Return true if the value is the smallest signed value.
Definition: Constants.cpp:153
void removeDeadConstantUsers() const
If there are any dead constant users dangling off of this constant, remove them.
Definition: Constants.cpp:475
Constant * getAggregateElement(unsigned Elt) const
For aggregates (struct/array/vector) return the constant that corresponds to the specified element if...
Definition: Constants.cpp:277
bool isZeroValue() const
Return true if the value is negative zero or null value.
Definition: Constants.cpp:66
bool isThreadDependent() const
Return true if the value can vary between threads.
Definition: Constants.cpp:401
Constant * stripPointerCasts()
Definition: Constant.h:157
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:46
This is an important base class in LLVM.
Definition: Constant.h:42
bool isDLLImportDependent() const
Return true if the value is dependent on a dllimport variable.
Definition: Constants.cpp:408
bool isNegativeZeroValue() const
Return true if the value is what would be returned by getZeroValueForNegation.
Definition: Constants.cpp:40
static Constant * getAllOnesValue(Type *Ty)
Get the all ones value.
Definition: Constants.cpp:261
const Constant * stripPointerCasts() const
Definition: Constant.h:153
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs, and aliases.
Definition: Value.cpp:558
Constant * getSplatValue() const
If this is a splat vector constant, meaning that all of the elements have the same value...
Definition: Constants.cpp:1273
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:244
ValueTy
Concrete subclass of this.
Definition: Value.h:446
void handleOperandChange(Value *, Value *)
This method is a special form of User::replaceUsesOfWith (which does not work on constants) that does...
Definition: Constants.cpp:2701
Class for arbitrary precision integers.
Definition: APInt.h:69
void destroyConstant()
Called if some element of this constant is no longer valid.
Definition: Constants.cpp:300
bool isOneValue() const
Returns true if the value is one.
Definition: Constants.cpp:127
LLVM Value Representation.
Definition: Value.h:73
void operator=(const Constant &)=delete
bool isNotMinSignedValue() const
Return true if the value is not the smallest signed value.
Definition: Constants.cpp:179