include/llvm/ADT/PointerIntPair.h

   1 //===- llvm/ADT/PointerIntPair.h - Pair for pointer and int -----*- 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 defines the PointerIntPair class.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #ifndef LLVM_ADT_POINTERINTPAIR_H
  14 #define LLVM_ADT_POINTERINTPAIR_H
  15
  16 #include "llvm/Support/PointerLikeTypeTraits.h"
  17 #include "llvm/Support/type_traits.h"
  18 #include <cassert>
  19 #include <cstdint>
  20 #include <limits>
  21
  22 namespace llvm {
  23
  24 template <typename T> struct DenseMapInfo;
  25 template <typename PointerT, unsigned IntBits, typename PtrTraits>
  26 struct PointerIntPairInfo;
  27
  28 /// PointerIntPair - This class implements a pair of a pointer and small
  29 /// integer.  It is designed to represent this in the space required by one
  30 /// pointer by bitmangling the integer into the low part of the pointer.  This
  31 /// can only be done for small integers: typically up to 3 bits, but it depends
  32 /// on the number of bits available according to PointerLikeTypeTraits for the
  33 /// type.
  34 ///
  35 /// Note that PointerIntPair always puts the IntVal part in the highest bits
  36 /// possible.  For example, PointerIntPair<void*, 1, bool> will put the bit for
  37 /// the bool into bit #2, not bit #0, which allows the low two bits to be used
  38 /// for something else.  For example, this allows:
  39 ///   PointerIntPair<PointerIntPair<void*, 1, bool>, 1, bool>
  40 /// ... and the two bools will land in different bits.
  41 template <typename PointerTy, unsigned IntBits, typename IntType = unsigned,
  42           typename PtrTraits = PointerLikeTypeTraits<PointerTy>,
  43           typename Info = PointerIntPairInfo<PointerTy, IntBits, PtrTraits>>
  44 class PointerIntPair {
  45   // Used by MSVC visualizer and generally helpful for debugging/visualizing.
  46   using InfoTy = Info;
  47   intptr_t Value = 0;
  48
  49 public:
  50   constexpr PointerIntPair() = default;
  51
  52   PointerIntPair(PointerTy PtrVal, IntType IntVal) {
  53     setPointerAndInt(PtrVal, IntVal);
  54   }
  55
  56   explicit PointerIntPair(PointerTy PtrVal) { initWithPointer(PtrVal); }
  57
  58   PointerTy getPointer() const { return Info::getPointer(Value); }
  59
  60   IntType getInt() const { return (IntType)Info::getInt(Value); }
  61
  62   void setPointer(PointerTy PtrVal) {
  63     Value = Info::updatePointer(Value, PtrVal);
  64   }
  65
  66   void setInt(IntType IntVal) {
  67     Value = Info::updateInt(Value, static_cast<intptr_t>(IntVal));
  68   }
  69
  70   void initWithPointer(PointerTy PtrVal) {
  71     Value = Info::updatePointer(0, PtrVal);
  72   }
  73
  74   void setPointerAndInt(PointerTy PtrVal, IntType IntVal) {
  75     Value = Info::updateInt(Info::updatePointer(0, PtrVal),
  76                             static_cast<intptr_t>(IntVal));
  77   }
  78
  79   PointerTy const *getAddrOfPointer() const {
  80     return const_cast<PointerIntPair *>(this)->getAddrOfPointer();
  81   }
  82
  83   PointerTy *getAddrOfPointer() {
  84     assert(Value == reinterpret_cast<intptr_t>(getPointer()) &&
  85            "Can only return the address if IntBits is cleared and "
  86            "PtrTraits doesn't change the pointer");
  87     return reinterpret_cast<PointerTy *>(&Value);
  88   }
  89
  90   void *getOpaqueValue() const { return reinterpret_cast<void *>(Value); }
  91
  92   void setFromOpaqueValue(void *Val) {
  93     Value = reinterpret_cast<intptr_t>(Val);
  94   }
  95
  96   static PointerIntPair getFromOpaqueValue(void *V) {
  97     PointerIntPair P;
  98     P.setFromOpaqueValue(V);
  99     return P;
 100   }
 101
 102   // Allow PointerIntPairs to be created from const void * if and only if the
 103   // pointer type could be created from a const void *.
 104   static PointerIntPair getFromOpaqueValue(const void *V) {
 105     (void)PtrTraits::getFromVoidPointer(V);
 106     return getFromOpaqueValue(const_cast<void *>(V));
 107   }
 108
 109   bool operator==(const PointerIntPair &RHS) const {
 110     return Value == RHS.Value;
 111   }
 112
 113   bool operator!=(const PointerIntPair &RHS) const {
 114     return Value != RHS.Value;
 115   }
 116
 117   bool operator<(const PointerIntPair &RHS) const { return Value < RHS.Value; }
 118   bool operator>(const PointerIntPair &RHS) const { return Value > RHS.Value; }
 119
 120   bool operator<=(const PointerIntPair &RHS) const {
 121     return Value <= RHS.Value;
 122   }
 123
 124   bool operator>=(const PointerIntPair &RHS) const {
 125     return Value >= RHS.Value;
 126   }
 127 };
 128
 129 // Specialize is_trivially_copyable to avoid limitation of llvm::is_trivially_copyable
 130 // when compiled with gcc 4.9.
 131 template <typename PointerTy, unsigned IntBits, typename IntType,
 132           typename PtrTraits,
 133           typename Info>
 134 struct is_trivially_copyable<PointerIntPair<PointerTy, IntBits, IntType, PtrTraits, Info>> : std::true_type {
 135 #ifdef HAVE_STD_IS_TRIVIALLY_COPYABLE
 136   static_assert(std::is_trivially_copyable<PointerIntPair<PointerTy, IntBits, IntType, PtrTraits, Info>>::value,
 137                 "inconsistent behavior between llvm:: and std:: implementation of is_trivially_copyable");
 138 #endif
 139 };
 140
 141
 142 template <typename PointerT, unsigned IntBits, typename PtrTraits>
 143 struct PointerIntPairInfo {
 144   static_assert(PtrTraits::NumLowBitsAvailable <
 145                     std::numeric_limits<uintptr_t>::digits,
 146                 "cannot use a pointer type that has all bits free");
 147   static_assert(IntBits <= PtrTraits::NumLowBitsAvailable,
 148                 "PointerIntPair with integer size too large for pointer");
 149   enum : uintptr_t {
 150     /// PointerBitMask - The bits that come from the pointer.
 151     PointerBitMask =
 152         ~(uintptr_t)(((intptr_t)1 << PtrTraits::NumLowBitsAvailable) - 1),
 153
 154     /// IntShift - The number of low bits that we reserve for other uses, and
 155     /// keep zero.
 156     IntShift = (uintptr_t)PtrTraits::NumLowBitsAvailable - IntBits,
 157
 158     /// IntMask - This is the unshifted mask for valid bits of the int type.
 159     IntMask = (uintptr_t)(((intptr_t)1 << IntBits) - 1),
 160
 161     // ShiftedIntMask - This is the bits for the integer shifted in place.
 162     ShiftedIntMask = (uintptr_t)(IntMask << IntShift)
 163   };
 164
 165   static PointerT getPointer(intptr_t Value) {
 166     return PtrTraits::getFromVoidPointer(
 167         reinterpret_cast<void *>(Value & PointerBitMask));
 168   }
 169
 170   static intptr_t getInt(intptr_t Value) {
 171     return (Value >> IntShift) & IntMask;
 172   }
 173
 174   static intptr_t updatePointer(intptr_t OrigValue, PointerT Ptr) {
 175     intptr_t PtrWord =
 176         reinterpret_cast<intptr_t>(PtrTraits::getAsVoidPointer(Ptr));
 177     assert((PtrWord & ~PointerBitMask) == 0 &&
 178            "Pointer is not sufficiently aligned");
 179     // Preserve all low bits, just update the pointer.
 180     return PtrWord | (OrigValue & ~PointerBitMask);
 181   }
 182
 183   static intptr_t updateInt(intptr_t OrigValue, intptr_t Int) {
 184     intptr_t IntWord = static_cast<intptr_t>(Int);
 185     assert((IntWord & ~IntMask) == 0 && "Integer too large for field");
 186
 187     // Preserve all bits other than the ones we are updating.
 188     return (OrigValue & ~ShiftedIntMask) | IntWord << IntShift;
 189   }
 190 };
 191
 192 // Provide specialization of DenseMapInfo for PointerIntPair.
 193 template <typename PointerTy, unsigned IntBits, typename IntType>
 194 struct DenseMapInfo<PointerIntPair<PointerTy, IntBits, IntType>> {
 195   using Ty = PointerIntPair<PointerTy, IntBits, IntType>;
 196
 197   static Ty getEmptyKey() {
 198     uintptr_t Val = static_cast<uintptr_t>(-1);
 199     Val <<= PointerLikeTypeTraits<Ty>::NumLowBitsAvailable;
 200     return Ty::getFromOpaqueValue(reinterpret_cast<void *>(Val));
 201   }
 202
 203   static Ty getTombstoneKey() {
 204     uintptr_t Val = static_cast<uintptr_t>(-2);
 205     Val <<= PointerLikeTypeTraits<PointerTy>::NumLowBitsAvailable;
 206     return Ty::getFromOpaqueValue(reinterpret_cast<void *>(Val));
 207   }
 208
 209   static unsigned getHashValue(Ty V) {
 210     uintptr_t IV = reinterpret_cast<uintptr_t>(V.getOpaqueValue());
 211     return unsigned(IV) ^ unsigned(IV >> 9);
 212   }
 213
 214   static bool isEqual(const Ty &LHS, const Ty &RHS) { return LHS == RHS; }
 215 };
 216
 217 // Teach SmallPtrSet that PointerIntPair is "basically a pointer".
 218 template <typename PointerTy, unsigned IntBits, typename IntType,
 219           typename PtrTraits>
 220 struct PointerLikeTypeTraits<
 221     PointerIntPair<PointerTy, IntBits, IntType, PtrTraits>> {
 222   static inline void *
 223   getAsVoidPointer(const PointerIntPair<PointerTy, IntBits, IntType> &P) {
 224     return P.getOpaqueValue();
 225   }
 226
 227   static inline PointerIntPair<PointerTy, IntBits, IntType>
 228   getFromVoidPointer(void *P) {
 229     return PointerIntPair<PointerTy, IntBits, IntType>::getFromOpaqueValue(P);
 230   }
 231
 232   static inline PointerIntPair<PointerTy, IntBits, IntType>
 233   getFromVoidPointer(const void *P) {
 234     return PointerIntPair<PointerTy, IntBits, IntType>::getFromOpaqueValue(P);
 235   }
 236
 237   enum { NumLowBitsAvailable = PtrTraits::NumLowBitsAvailable - IntBits };
 238 };
 239
 240 } // end namespace llvm
 241
 242 #endif // LLVM_ADT_POINTERINTPAIR_H