PointerUnion.h revision 41222823db11107834414a378525bb21493d3a1f 
1//===- llvm/ADT/PointerUnion.h - Discriminated Union of 2 Ptrs --*- 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 PointerUnion class, which is a discriminated union of
11// pointer types.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ADT_POINTERUNION_H
16#define LLVM_ADT_POINTERUNION_H
17
18#include "llvm/ADT/PointerIntPair.h"
19
20namespace llvm {
21
22  /// getPointerUnionTypeNum - If the argument has type PT1* or PT2* return
23  /// false or true respectively.
24  template <typename PT1, typename PT2>
25  static inline int getPointerUnionTypeNum(PT1 *P) { return 0; }
26  template <typename PT1, typename PT2>
27  static inline int getPointerUnionTypeNum(PT2 *P) { return 1; }
28  template <typename PT1, typename PT2>
29  static inline int getPointerUnionTypeNum(...) { return -1; }
30
31
32  /// Provide PointerLikeTypeTraits for void* that is used by PointerUnion
33  /// for the two template arguments.
34  template <typename PT1, typename PT2>
35  class PointerUnionUIntTraits {
36  public:
37    static inline void *getAsVoidPointer(void *P) { return P; }
38    static inline void *getFromVoidPointer(void *P) { return P; }
39    enum {
40      PT1BitsAv = PointerLikeTypeTraits<PT1>::NumLowBitsAvailable,
41      PT2BitsAv = PointerLikeTypeTraits<PT2>::NumLowBitsAvailable,
42      NumLowBitsAvailable = PT1BitsAv < PT2BitsAv ? PT1BitsAv : PT2BitsAv
43    };
44  };
45
46  /// PointerUnion - This implements a discriminated union of two pointer types,
47  /// and keeps the discriminator bit-mangled into the low bits of the pointer.
48  /// This allows the implementation to be extremely efficient in space, but
49  /// permits a very natural and type-safe API.
50  ///
51  /// Common use patterns would be something like this:
52  ///    PointerUnion<int*, float*> P;
53  ///    P = (int*)0;
54  ///    printf("%d %d", P.is<int*>(), P.is<float*>());  // prints "1 0"
55  ///    X = P.get<int*>();     // ok.
56  ///    Y = P.get<float*>();   // runtime assertion failure.
57  ///    Z = P.get<double*>();  // runtime assertion failure (regardless of tag)
58  ///    P = (float*)0;
59  ///    Y = P.get<float*>();   // ok.
60  ///    X = P.get<int*>();     // runtime assertion failure.
61  template <typename PT1, typename PT2>
62  class PointerUnion {
63  public:
64    typedef PointerIntPair<void*, 1, bool,
65                           PointerUnionUIntTraits<PT1,PT2> > ValTy;
66  private:
67    ValTy Val;
68  public:
69    PointerUnion() {}
70
71    PointerUnion(PT1 V) {
72      Val.setPointer(
73         const_cast<void *>(PointerLikeTypeTraits<PT1>::getAsVoidPointer(V)));
74      Val.setInt(0);
75    }
76    PointerUnion(PT2 V) {
77      Val.setPointer(
78         const_cast<void *>(PointerLikeTypeTraits<PT2>::getAsVoidPointer(V)));
79      Val.setInt(1);
80    }
81
82    /// isNull - Return true if the pointer help in the union is null,
83    /// regardless of which type it is.
84    bool isNull() const { return Val.getPointer() == 0; }
85    operator bool() const { return !isNull(); }
86
87    /// is<T>() return true if the Union currently holds the type matching T.
88    template<typename T>
89    int is() const {
90      int TyNo = ::llvm::getPointerUnionTypeNum<PT1, PT2>((T*)0);
91      assert(TyNo != -1 && "Type query could never succeed on PointerUnion!");
92      return Val.getInt() == TyNo;
93    }
94
95    /// get<T>() - Return the value of the specified pointer type. If the
96    /// specified pointer type is incorrect, assert.
97    template<typename T>
98    T get() const {
99      assert(is<T>() && "Invalid accessor called");
100      return PointerLikeTypeTraits<T>::getFromVoidPointer(Val.getPointer());
101    }
102
103    /// dyn_cast<T>() - If the current value is of the specified pointer type,
104    /// return it, otherwise return null.
105    template<typename T>
106    T dyn_cast() const {
107      if (is<T>()) return get<T>();
108      return T();
109    }
110
111    /// Assignment operators - Allow assigning into this union from either
112    /// pointer type, setting the discriminator to remember what it came from.
113    const PointerUnion &operator=(const PT1 &RHS) {
114      Val.setPointer(
115         const_cast<void *>(PointerLikeTypeTraits<PT1>::getAsVoidPointer(RHS)));
116      Val.setInt(0);
117      return *this;
118    }
119    const PointerUnion &operator=(const PT2 &RHS) {
120      Val.setPointer(
121        const_cast<void *>(PointerLikeTypeTraits<PT2>::getAsVoidPointer(RHS)));
122      Val.setInt(1);
123      return *this;
124    }
125
126    void *getOpaqueValue() const { return Val.getOpaqueValue(); }
127    static PointerUnion getFromOpaqueValue(void *VP) {
128      PointerUnion V;
129      V.Val = ValTy::getFromOpaqueValue(VP);
130      return V;
131    }
132  };
133
134  // Teach SmallPtrSet that PointerUnion is "basically a pointer", that has
135  // # low bits available = min(PT1bits,PT2bits)-1.
136  template<typename PT1, typename PT2>
137  class PointerLikeTypeTraits<PointerUnion<PT1, PT2> > {
138  public:
139    static inline void *
140    getAsVoidPointer(const PointerUnion<PT1, PT2> &P) {
141      return P.getOpaqueValue();
142    }
143    static inline PointerUnion<PT1, PT2>
144    getFromVoidPointer(void *P) {
145      return PointerUnion<PT1, PT2>::getFromOpaqueValue(P);
146    }
147
148    // The number of bits available are the min of the two pointer types.
149    enum {
150      NumLowBitsAvailable =
151        PointerLikeTypeTraits<typename PointerUnion<PT1,PT2>::ValTy>
152          ::NumLowBitsAvailable
153    };
154  };
155
156
157  /// PointerUnion3 - This is a pointer union of three pointer types.  See
158  /// documentation for PointerUnion for usage.
159  template <typename PT1, typename PT2, typename PT3>
160  class PointerUnion3 {
161  public:
162    typedef PointerUnion<PT1, PT2> InnerUnion;
163    typedef PointerUnion<InnerUnion, PT3> ValTy;
164  private:
165    ValTy Val;
166  public:
167    PointerUnion3() {}
168
169    PointerUnion3(PT1 V) {
170      Val = InnerUnion(V);
171    }
172    PointerUnion3(PT2 V) {
173      Val = InnerUnion(V);
174    }
175    PointerUnion3(PT3 V) {
176      Val = V;
177    }
178
179    /// isNull - Return true if the pointer help in the union is null,
180    /// regardless of which type it is.
181    bool isNull() const { return Val.isNull(); }
182    operator bool() const { return !isNull(); }
183
184    /// is<T>() return true if the Union currently holds the type matching T.
185    template<typename T>
186    int is() const {
187      // Is it PT1/PT2?
188      if (::llvm::getPointerUnionTypeNum<PT1, PT2>((T*)0) != -1)
189        return Val.is<InnerUnion>() && Val.get<InnerUnion>().is<T>();
190      return Val.is<T>();
191    }
192
193    /// get<T>() - Return the value of the specified pointer type. If the
194    /// specified pointer type is incorrect, assert.
195    template<typename T>
196    T get() const {
197      assert(is<T>() && "Invalid accessor called");
198      // Is it PT1/PT2?
199      if (::llvm::getPointerUnionTypeNum<PT1, PT2>((T*)0) != -1)
200        return Val.get<InnerUnion>().get<T>();
201
202      return Val.get<T>();
203    }
204
205    /// dyn_cast<T>() - If the current value is of the specified pointer type,
206    /// return it, otherwise return null.
207    template<typename T>
208    T dyn_cast() const {
209      if (is<T>()) return get<T>();
210      return T();
211    }
212
213    /// Assignment operators - Allow assigning into this union from either
214    /// pointer type, setting the discriminator to remember what it came from.
215    const PointerUnion3 &operator=(const PT1 &RHS) {
216      Val = InnerUnion(RHS);
217      return *this;
218    }
219    const PointerUnion3 &operator=(const PT2 &RHS) {
220      Val = InnerUnion(RHS);
221      return *this;
222    }
223    const PointerUnion3 &operator=(const PT3 &RHS) {
224      Val = RHS;
225      return *this;
226    }
227
228    void *getOpaqueValue() const { return Val.getOpaqueValue(); }
229    static PointerUnion3 getFromOpaqueValue(void *VP) {
230      PointerUnion3 V;
231      V.Val = ValTy::getFromOpaqueValue(VP);
232      return V;
233    }
234  };
235
236  // Teach SmallPtrSet that PointerUnion3 is "basically a pointer", that has
237  // # low bits available = min(PT1bits,PT2bits,PT2bits)-2.
238  template<typename PT1, typename PT2, typename PT3>
239  class PointerLikeTypeTraits<PointerUnion3<PT1, PT2, PT3> > {
240  public:
241    static inline void *
242    getAsVoidPointer(const PointerUnion3<PT1, PT2, PT3> &P) {
243      return P.getOpaqueValue();
244    }
245    static inline PointerUnion3<PT1, PT2, PT3>
246    getFromVoidPointer(void *P) {
247      return PointerUnion3<PT1, PT2, PT3>::getFromOpaqueValue(P);
248    }
249
250    // The number of bits available are the min of the two pointer types.
251    enum {
252      NumLowBitsAvailable =
253        PointerLikeTypeTraits<typename PointerUnion3<PT1, PT2, PT3>::ValTy>
254          ::NumLowBitsAvailable
255    };
256  };
257}
258
259#endif
260