include/llvm/IR/Constant.h

   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;
 129   Constant *getAggregateElement(Constant *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
 187   Constant *stripPointerCasts() {
 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