LLVM  10.0.0svn
Constant.h
Go to the documentation of this file.
1 //===-- llvm/Constant.h - Constant class definition -------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file contains the declaration of the Constant class.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_IR_CONSTANT_H
14 #define LLVM_IR_CONSTANT_H
15 
16 #include "llvm/IR/User.h"
17 #include "llvm/IR/Value.h"
18 #include "llvm/Support/Casting.h"
19 
20 namespace llvm {
21 
22 class APInt;
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 /// LLVM Constant Representation
41 class Constant : public User {
42 protected:
43  Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
44  : User(ty, vty, Ops, NumOps) {}
45 
46 public:
47  void operator=(const Constant &) = delete;
48  Constant(const Constant &) = delete;
49 
50  /// Return true if this is the value that would be returned by getNullValue.
51  bool isNullValue() const;
52 
53  /// Returns true if the value is one.
54  bool isOneValue() const;
55 
56  /// Return true if this is the value that would be returned by
57  /// getAllOnesValue.
58  bool isAllOnesValue() const;
59 
60  /// Return true if the value is what would be returned by
61  /// getZeroValueForNegation.
62  bool isNegativeZeroValue() const;
63 
64  /// Return true if the value is negative zero or null value.
65  bool isZeroValue() const;
66 
67  /// Return true if the value is not the smallest signed value.
68  bool isNotMinSignedValue() const;
69 
70  /// Return true if the value is the smallest signed value.
71  bool isMinSignedValue() const;
72 
73  /// Return true if this is a finite and non-zero floating-point scalar
74  /// constant or a vector constant with all finite and non-zero elements.
75  bool isFiniteNonZeroFP() const;
76 
77  /// Return true if this is a normal (as opposed to denormal) floating-point
78  /// scalar constant or a vector constant with all normal elements.
79  bool isNormalFP() const;
80 
81  /// Return true if this scalar has an exact multiplicative inverse or this
82  /// vector has an exact multiplicative inverse for each element in the vector.
83  bool hasExactInverseFP() const;
84 
85  /// Return true if this is a floating-point NaN constant or a vector
86  /// floating-point constant with all NaN elements.
87  bool isNaN() const;
88 
89  /// Return true if this constant and a constant 'Y' are element-wise equal.
90  /// This is identical to just comparing the pointers, with the exception that
91  /// for vectors, if only one of the constants has an `undef` element in some
92  /// lane, the constants still match.
93  bool isElementWiseEqual(Value *Y) const;
94 
95  /// Return true if this is a vector constant that includes any undefined
96  /// elements.
97  bool containsUndefElement() const;
98 
99  /// Return true if this is a vector constant that includes any constant
100  /// expressions.
101  bool containsConstantExpression() const;
102 
103  /// Return true if evaluation of this constant could trap. This is true for
104  /// things like constant expressions that could divide by zero.
105  bool canTrap() const;
106 
107  /// Return true if the value can vary between threads.
108  bool isThreadDependent() const;
109 
110  /// Return true if the value is dependent on a dllimport variable.
111  bool isDLLImportDependent() const;
112 
113  /// Return true if the constant has users other than constant expressions and
114  /// other dangling things.
115  bool isConstantUsed() const;
116 
117  /// This method classifies the entry according to whether or not it may
118  /// generate a relocation entry. This must be conservative, so if it might
119  /// codegen to a relocatable entry, it should say so.
120  ///
121  /// FIXME: This really should not be in IR.
122  bool needsRelocation() const;
123 
124  /// For aggregates (struct/array/vector) return the constant that corresponds
125  /// to the specified element if possible, or null if not. This can return null
126  /// if the element index is a ConstantExpr, if 'this' is a constant expr or
127  /// if the constant does not fit into an uint64_t.
128  Constant *getAggregateElement(unsigned Elt) const;
130 
131  /// If this is a splat vector constant, meaning that all of the elements have
132  /// the same value, return that value. Otherwise return 0.
133  Constant *getSplatValue() const;
134 
135  /// If C is a constant integer then return its value, otherwise C must be a
136  /// vector of constant integers, all equal, and the common value is returned.
137  const APInt &getUniqueInteger() const;
138 
139  /// Called if some element of this constant is no longer valid.
140  /// At this point only other constants may be on the use_list for this
141  /// constant. Any constants on our Use list must also be destroy'd. The
142  /// implementation must be sure to remove the constant from the list of
143  /// available cached constants. Implementations should implement
144  /// destroyConstantImpl to remove constants from any pools/maps they are
145  /// contained it.
146  void destroyConstant();
147 
148  //// Methods for support type inquiry through isa, cast, and dyn_cast:
149  static bool classof(const Value *V) {
150  static_assert(ConstantFirstVal == 0, "V->getValueID() >= ConstantFirstVal always succeeds");
151  return V->getValueID() <= ConstantLastVal;
152  }
153 
154  /// This method is a special form of User::replaceUsesOfWith
155  /// (which does not work on constants) that does work
156  /// on constants. Basically this method goes through the trouble of building
157  /// a new constant that is equivalent to the current one, with all uses of
158  /// From replaced with uses of To. After this construction is completed, all
159  /// of the users of 'this' are replaced to use the new constant, and then
160  /// 'this' is deleted. In general, you should not call this method, instead,
161  /// use Value::replaceAllUsesWith, which automatically dispatches to this
162  /// method as needed.
163  ///
164  void handleOperandChange(Value *, Value *);
165 
166  static Constant *getNullValue(Type* Ty);
167 
168  /// @returns the value for an integer or vector of integer constant of the
169  /// given type that has all its bits set to true.
170  /// Get the all ones value
171  static Constant *getAllOnesValue(Type* Ty);
172 
173  /// Return the value for an integer or pointer constant, or a vector thereof,
174  /// with the given scalar value.
175  static Constant *getIntegerValue(Type *Ty, const APInt &V);
176 
177  /// If there are any dead constant users dangling off of this constant, remove
178  /// them. This method is useful for clients that want to check to see if a
179  /// global is unused, but don't want to deal with potentially dead constants
180  /// hanging off of the globals.
181  void removeDeadConstantUsers() const;
182 
183  const Constant *stripPointerCasts() const {
184  return cast<Constant>(Value::stripPointerCasts());
185  }
186 
188  return const_cast<Constant*>(
189  static_cast<const Constant *>(this)->stripPointerCasts());
190  }
191 };
192 
193 } // end namespace llvm
194 
195 #endif // LLVM_IR_CONSTANT_H
bool isAllOnesValue() const
Return true if this is the value that would be returned by getAllOnesValue.
Definition: Constants.cpp:100
unsigned getValueID() const
Return an ID for the concrete type of this object.
Definition: Value.h:483
bool isNaN() const
Return true if this is a floating-point NaN constant or a vector floating-point constant with all NaN...
Definition: Constants.cpp:241
This class represents lattice values for constants.
Definition: AllocatorList.h:23
bool needsRelocation() const
This method classifies the entry according to whether or not it may generate a relocation entry...
Definition: Constants.cpp:513
bool isConstantUsed() const
Return true if the constant has users other than constant expressions and other dangling things...
Definition: Constants.cpp:501
static bool classof(const Value *V)
Definition: Constant.h:149
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:1420
static Constant * getNullValue(Type *Ty)
Constructor to create a &#39;0&#39; constant of arbitrary type.
Definition: Constants.cpp:289
static GCMetadataPrinterRegistry::Add< OcamlGCMetadataPrinter > Y("ocaml", "ocaml 3.10-compatible collector")
A Use represents the edge between a Value definition and its users.
Definition: Use.h:55
bool isNullValue() const
Return true if this is the value that would be returned by getNullValue.
Definition: Constants.cpp:85
bool canTrap() const
Return true if evaluation of this constant could trap.
Definition: Constants.cpp:457
bool isFiniteNonZeroFP() const
Return true if this is a finite and non-zero floating-point scalar constant or a vector constant with...
Definition: Constants.cpp:202
Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
Definition: Constant.h:43
bool isMinSignedValue() const
Return true if the value is the smallest signed value.
Definition: Constants.cpp:152
void removeDeadConstantUsers() const
If there are any dead constant users dangling off of this constant, remove them.
Definition: Constants.cpp:571
Constant * getAggregateElement(unsigned Elt) const
For aggregates (struct/array/vector) return the constant that corresponds to the specified element if...
Definition: Constants.cpp:359
bool isZeroValue() const
Return true if the value is negative zero or null value.
Definition: Constants.cpp:65
bool isThreadDependent() const
Return true if the value can vary between threads.
Definition: Constants.cpp:487
Constant * stripPointerCasts()
Definition: Constant.h:187
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:45
This is an important base class in LLVM.
Definition: Constant.h:41
bool isDLLImportDependent() const
Return true if the value is dependent on a dllimport variable.
Definition: Constants.cpp:494
bool isNegativeZeroValue() const
Return true if the value is what would be returned by getZeroValueForNegation.
Definition: Constants.cpp:39
static Constant * getAllOnesValue(Type *Ty)
Definition: Constants.cpp:343
const Constant * stripPointerCasts() const
Definition: Constant.h:183
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs and address space casts.
Definition: Value.cpp:525
Constant * getSplatValue() const
If this is a splat vector constant, meaning that all of the elements have the same value...
Definition: Constants.cpp:1399
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:326
bool isNormalFP() const
Return true if this is a normal (as opposed to denormal) floating-point scalar constant or a vector c...
Definition: Constants.cpp:215
bool containsUndefElement() const
Return true if this is a vector constant that includes any undefined elements.
Definition: Constants.cpp:268
ValueTy
Concrete subclass of this.
Definition: Value.h:464
void handleOperandChange(Value *, Value *)
This method is a special form of User::replaceUsesOfWith (which does not work on constants) that does...
Definition: Constants.cpp:2829
Class for arbitrary precision integers.
Definition: APInt.h:69
bool containsConstantExpression() const
Return true if this is a vector constant that includes any constant expressions.
Definition: Constants.cpp:278
void destroyConstant()
Called if some element of this constant is no longer valid.
Definition: Constants.cpp:386
bool isOneValue() const
Returns true if the value is one.
Definition: Constants.cpp:126
LLVM Value Representation.
Definition: Value.h:73
void operator=(const Constant &)=delete
bool hasExactInverseFP() const
Return true if this scalar has an exact multiplicative inverse or this vector has an exact multiplica...
Definition: Constants.cpp:228
bool isNotMinSignedValue() const
Return true if the value is not the smallest signed value.
Definition: Constants.cpp:178
bool isElementWiseEqual(Value *Y) const
Return true if this constant and a constant &#39;Y&#39; are element-wise equal.
Definition: Constants.cpp:254