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 
66 public:
PointerIntPair()67   PointerIntPair() : Value(0) {}
PointerIntPair(PointerTy PtrVal,IntType IntVal)68   PointerIntPair(PointerTy PtrVal, IntType IntVal) {
69     setPointerAndInt(PtrVal, IntVal);
70   }
PointerIntPair(PointerTy PtrVal)71   explicit PointerIntPair(PointerTy PtrVal) {
72     initWithPointer(PtrVal);
73   }
74 
getPointer()75   PointerTy getPointer() const {
76     return PtrTraits::getFromVoidPointer(
77                          reinterpret_cast<void*>(Value & PointerBitMask));
78   }
79 
getInt()80   IntType getInt() const {
81     return (IntType)((Value >> IntShift) & IntMask);
82   }
83 
setPointer(PointerTy PtrVal)84   void setPointer(PointerTy PtrVal) {
85     intptr_t PtrWord
86       = reinterpret_cast<intptr_t>(PtrTraits::getAsVoidPointer(PtrVal));
87     assert((PtrWord & ~PointerBitMask) == 0 &&
88            "Pointer is not sufficiently aligned");
89     // Preserve all low bits, just update the pointer.
90     Value = PtrWord | (Value & ~PointerBitMask);
91   }
92 
setInt(IntType IntVal)93   void setInt(IntType IntVal) {
94     intptr_t IntWord = static_cast<intptr_t>(IntVal);
95     assert((IntWord & ~IntMask) == 0 && "Integer too large for field");
96 
97     // Preserve all bits other than the ones we are updating.
98     Value &= ~ShiftedIntMask;     // Remove integer field.
99     Value |= IntWord << IntShift;  // Set new integer.
100   }
101 
initWithPointer(PointerTy PtrVal)102   void initWithPointer(PointerTy PtrVal) {
103     intptr_t PtrWord
104       = reinterpret_cast<intptr_t>(PtrTraits::getAsVoidPointer(PtrVal));
105     assert((PtrWord & ~PointerBitMask) == 0 &&
106            "Pointer is not sufficiently aligned");
107     Value = PtrWord;
108   }
109 
setPointerAndInt(PointerTy PtrVal,IntType IntVal)110   void setPointerAndInt(PointerTy PtrVal, IntType IntVal) {
111     intptr_t PtrWord
112       = reinterpret_cast<intptr_t>(PtrTraits::getAsVoidPointer(PtrVal));
113     assert((PtrWord & ~PointerBitMask) == 0 &&
114            "Pointer is not sufficiently aligned");
115     intptr_t IntWord = static_cast<intptr_t>(IntVal);
116     assert((IntWord & ~IntMask) == 0 && "Integer too large for field");
117 
118     Value = PtrWord | (IntWord << IntShift);
119   }
120 
getAddrOfPointer()121   PointerTy const *getAddrOfPointer() const {
122     return const_cast<PointerIntPair *>(this)->getAddrOfPointer();
123   }
124 
getAddrOfPointer()125   PointerTy *getAddrOfPointer() {
126     assert(Value == reinterpret_cast<intptr_t>(getPointer()) &&
127            "Can only return the address if IntBits is cleared and "
128            "PtrTraits doesn't change the pointer");
129     return reinterpret_cast<PointerTy *>(&Value);
130   }
131 
getOpaqueValue()132   void *getOpaqueValue() const { return reinterpret_cast<void*>(Value); }
setFromOpaqueValue(void * Val)133   void setFromOpaqueValue(void *Val) { Value = reinterpret_cast<intptr_t>(Val);}
134 
getFromOpaqueValue(void * V)135   static PointerIntPair getFromOpaqueValue(void *V) {
136     PointerIntPair P;
137     P.setFromOpaqueValue(V);
138     return P;
139   }
140 
141   // Allow PointerIntPairs to be created from const void * if and only if the
142   // pointer type could be created from a const void *.
getFromOpaqueValue(const void * V)143   static PointerIntPair getFromOpaqueValue(const void *V) {
144     (void)PtrTraits::getFromVoidPointer(V);
145     return getFromOpaqueValue(const_cast<void *>(V));
146   }
147 
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   bool operator>(const PointerIntPair &RHS) const {return Value > RHS.Value;}
152   bool operator<=(const PointerIntPair &RHS) const {return Value <= RHS.Value;}
153   bool operator>=(const PointerIntPair &RHS) const {return Value >= RHS.Value;}
154 };
155 
156 template <typename T> struct isPodLike;
157 template<typename PointerTy, unsigned IntBits, typename IntType>
158 struct isPodLike<PointerIntPair<PointerTy, IntBits, IntType> > {
159    static const bool value = true;
160 };
161 
162 // Provide specialization of DenseMapInfo for PointerIntPair.
163 template<typename PointerTy, unsigned IntBits, typename IntType>
164 struct DenseMapInfo<PointerIntPair<PointerTy, IntBits, IntType> > {
165   typedef PointerIntPair<PointerTy, IntBits, IntType> Ty;
166   static Ty getEmptyKey() {
167     uintptr_t Val = static_cast<uintptr_t>(-1);
168     Val <<= PointerLikeTypeTraits<Ty>::NumLowBitsAvailable;
169     return Ty::getFromOpaqueValue(reinterpret_cast<void *>(Val));
170   }
171   static Ty getTombstoneKey() {
172     uintptr_t Val = static_cast<uintptr_t>(-2);
173     Val <<= PointerLikeTypeTraits<PointerTy>::NumLowBitsAvailable;
174     return Ty::getFromOpaqueValue(reinterpret_cast<void *>(Val));
175   }
176   static unsigned getHashValue(Ty V) {
177     uintptr_t IV = reinterpret_cast<uintptr_t>(V.getOpaqueValue());
178     return unsigned(IV) ^ unsigned(IV >> 9);
179   }
180   static bool isEqual(const Ty &LHS, const Ty &RHS) { return LHS == RHS; }
181 };
182 
183 // Teach SmallPtrSet that PointerIntPair is "basically a pointer".
184 template<typename PointerTy, unsigned IntBits, typename IntType,
185          typename PtrTraits>
186 class PointerLikeTypeTraits<PointerIntPair<PointerTy, IntBits, IntType,
187                                            PtrTraits> > {
188 public:
189   static inline void *
190   getAsVoidPointer(const PointerIntPair<PointerTy, IntBits, IntType> &P) {
191     return P.getOpaqueValue();
192   }
193   static inline PointerIntPair<PointerTy, IntBits, IntType>
194   getFromVoidPointer(void *P) {
195     return PointerIntPair<PointerTy, IntBits, IntType>::getFromOpaqueValue(P);
196   }
197   static inline PointerIntPair<PointerTy, IntBits, IntType>
198   getFromVoidPointer(const void *P) {
199     return PointerIntPair<PointerTy, IntBits, IntType>::getFromOpaqueValue(P);
200   }
201   enum {
202     NumLowBitsAvailable = PtrTraits::NumLowBitsAvailable - IntBits
203   };
204 };
205 
206 } // end namespace llvm
207 #endif
208