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