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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/DenseMapInfo.h"
19 #include "llvm/ADT/PointerIntPair.h"
20 #include "llvm/Support/PointerLikeTypeTraits.h"
21 #include <cassert>
22 #include <cstdint>
23 #include <cstddef>
24 
25 namespace llvm {
26 
27 template <typename T> struct PointerUnionTypeSelectorReturn {
28   typedef T Return;
29 };
30 
31 /// Get a type based on whether two types are the same or not.
32 ///
33 /// For:
34 ///
35 /// \code
36 ///   typedef typename PointerUnionTypeSelector<T1, T2, EQ, NE>::Return Ret;
37 /// \endcode
38 ///
39 /// Ret will be EQ type if T1 is same as T2 or NE type otherwise.
40 template <typename T1, typename T2, typename RET_EQ, typename RET_NE>
41 struct PointerUnionTypeSelector {
42   typedef typename PointerUnionTypeSelectorReturn<RET_NE>::Return Return;
43 };
44 
45 template <typename T, typename RET_EQ, typename RET_NE>
46 struct PointerUnionTypeSelector<T, T, RET_EQ, RET_NE> {
47   typedef typename PointerUnionTypeSelectorReturn<RET_EQ>::Return Return;
48 };
49 
50 template <typename T1, typename T2, typename RET_EQ, typename RET_NE>
51 struct PointerUnionTypeSelectorReturn<
52     PointerUnionTypeSelector<T1, T2, RET_EQ, RET_NE>> {
53   typedef
54       typename PointerUnionTypeSelector<T1, T2, RET_EQ, RET_NE>::Return Return;
55 };
56 
57 /// Provide PointerLikeTypeTraits for void* that is used by PointerUnion
58 /// for the two template arguments.
59 template <typename PT1, typename PT2> class PointerUnionUIntTraits {
60 public:
61   static inline void *getAsVoidPointer(void *P) { return P; }
62   static inline void *getFromVoidPointer(void *P) { return P; }
63 
64   enum {
65     PT1BitsAv = (int)(PointerLikeTypeTraits<PT1>::NumLowBitsAvailable),
66     PT2BitsAv = (int)(PointerLikeTypeTraits<PT2>::NumLowBitsAvailable),
67     NumLowBitsAvailable = PT1BitsAv < PT2BitsAv ? PT1BitsAv : PT2BitsAv
68   };
69 };
70 
71 /// A discriminated union of two pointer types, with the discriminator in the
72 /// low bit of the pointer.
73 ///
74 /// This implementation is extremely efficient in space due to leveraging the
75 /// low bits of the pointer, while exposing a natural and type-safe API.
76 ///
77 /// Common use patterns would be something like this:
78 ///    PointerUnion<int*, float*> P;
79 ///    P = (int*)0;
80 ///    printf("%d %d", P.is<int*>(), P.is<float*>());  // prints "1 0"
81 ///    X = P.get<int*>();     // ok.
82 ///    Y = P.get<float*>();   // runtime assertion failure.
83 ///    Z = P.get<double*>();  // compile time failure.
84 ///    P = (float*)0;
85 ///    Y = P.get<float*>();   // ok.
86 ///    X = P.get<int*>();     // runtime assertion failure.
87 template <typename PT1, typename PT2> class PointerUnion {
88 public:
89   typedef PointerIntPair<void *, 1, bool, PointerUnionUIntTraits<PT1, PT2>>
90       ValTy;
91 
92 private:
93   ValTy Val;
94 
95   struct IsPT1 {
96     static const int Num = 0;
97   };
98   struct IsPT2 {
99     static const int Num = 1;
100   };
101   template <typename T> struct UNION_DOESNT_CONTAIN_TYPE {};
102 
103 public:
104   PointerUnion() = default;
105 
106   PointerUnion(PT1 V)
107       : Val(const_cast<void *>(
108             PointerLikeTypeTraits<PT1>::getAsVoidPointer(V))) {}
109   PointerUnion(PT2 V)
110       : Val(const_cast<void *>(PointerLikeTypeTraits<PT2>::getAsVoidPointer(V)),
111             1) {}
112 
113   /// Test if the pointer held in the union is null, regardless of
114   /// which type it is.
115   bool isNull() const {
116     // Convert from the void* to one of the pointer types, to make sure that
117     // we recursively strip off low bits if we have a nested PointerUnion.
118     return !PointerLikeTypeTraits<PT1>::getFromVoidPointer(Val.getPointer());
119   }
120   explicit operator bool() const { return !isNull(); }
121 
122   /// Test if the Union currently holds the type matching T.
123   template <typename T> int is() const {
124     typedef typename ::llvm::PointerUnionTypeSelector<
125         PT1, T, IsPT1, ::llvm::PointerUnionTypeSelector<
126                            PT2, T, IsPT2, UNION_DOESNT_CONTAIN_TYPE<T>>>::Return
127         Ty;
128     int TyNo = Ty::Num;
129     return static_cast<int>(Val.getInt()) == TyNo;
130   }
131 
132   /// Returns the value of the specified pointer type.
133   ///
134   /// If the specified pointer type is incorrect, assert.
135   template <typename T> T get() const {
136     assert(is<T>() && "Invalid accessor called");
137     return PointerLikeTypeTraits<T>::getFromVoidPointer(Val.getPointer());
138   }
139 
140   /// Returns the current pointer if it is of the specified pointer type,
141   /// otherwises returns null.
142   template <typename T> T dyn_cast() const {
143     if (is<T>())
144       return get<T>();
145     return T();
146   }
147 
148   /// If the union is set to the first pointer type get an address pointing to
149   /// it.
150   PT1 const *getAddrOfPtr1() const {
151     return const_cast<PointerUnion *>(this)->getAddrOfPtr1();
152   }
153 
154   /// If the union is set to the first pointer type get an address pointing to
155   /// it.
156   PT1 *getAddrOfPtr1() {
157     assert(is<PT1>() && "Val is not the first pointer");
158     assert(
159         get<PT1>() == Val.getPointer() &&
160         "Can't get the address because PointerLikeTypeTraits changes the ptr");
161     return (PT1 *)Val.getAddrOfPointer();
162   }
163 
164   /// Assignment from nullptr which just clears the union.
165   const PointerUnion &operator=(std::nullptr_t) {
166     Val.initWithPointer(nullptr);
167     return *this;
168   }
169 
170   /// Assignment operators - Allow assigning into this union from either
171   /// pointer type, setting the discriminator to remember what it came from.
172   const PointerUnion &operator=(const PT1 &RHS) {
173     Val.initWithPointer(
174         const_cast<void *>(PointerLikeTypeTraits<PT1>::getAsVoidPointer(RHS)));
175     return *this;
176   }
177   const PointerUnion &operator=(const PT2 &RHS) {
178     Val.setPointerAndInt(
179         const_cast<void *>(PointerLikeTypeTraits<PT2>::getAsVoidPointer(RHS)),
180         1);
181     return *this;
182   }
183 
184   void *getOpaqueValue() const { return Val.getOpaqueValue(); }
185   static inline PointerUnion getFromOpaqueValue(void *VP) {
186     PointerUnion V;
187     V.Val = ValTy::getFromOpaqueValue(VP);
188     return V;
189   }
190 };
191 
192 template <typename PT1, typename PT2>
193 static bool operator==(PointerUnion<PT1, PT2> lhs, PointerUnion<PT1, PT2> rhs) {
194   return lhs.getOpaqueValue() == rhs.getOpaqueValue();
195 }
196 
197 template <typename PT1, typename PT2>
198 static bool operator!=(PointerUnion<PT1, PT2> lhs, PointerUnion<PT1, PT2> rhs) {
199   return lhs.getOpaqueValue() != rhs.getOpaqueValue();
200 }
201 
202 template <typename PT1, typename PT2>
203 static bool operator<(PointerUnion<PT1, PT2> lhs, PointerUnion<PT1, PT2> rhs) {
204   return lhs.getOpaqueValue() < rhs.getOpaqueValue();
205 }
206 
207 // Teach SmallPtrSet that PointerUnion is "basically a pointer", that has
208 // # low bits available = min(PT1bits,PT2bits)-1.
209 template <typename PT1, typename PT2>
210 class PointerLikeTypeTraits<PointerUnion<PT1, PT2>> {
211 public:
212   static inline void *getAsVoidPointer(const PointerUnion<PT1, PT2> &P) {
213     return P.getOpaqueValue();
214   }
215 
216   static inline PointerUnion<PT1, PT2> getFromVoidPointer(void *P) {
217     return PointerUnion<PT1, PT2>::getFromOpaqueValue(P);
218   }
219 
220   // The number of bits available are the min of the two pointer types.
221   enum {
222     NumLowBitsAvailable = PointerLikeTypeTraits<
223         typename PointerUnion<PT1, PT2>::ValTy>::NumLowBitsAvailable
224   };
225 };
226 
227 /// A pointer union of three pointer types. See documentation for PointerUnion
228 /// for usage.
229 template <typename PT1, typename PT2, typename PT3> class PointerUnion3 {
230 public:
231   typedef PointerUnion<PT1, PT2> InnerUnion;
232   typedef PointerUnion<InnerUnion, PT3> ValTy;
233 
234 private:
235   ValTy Val;
236 
237   struct IsInnerUnion {
238     ValTy Val;
239     IsInnerUnion(ValTy val) : Val(val) {}
240     template <typename T> int is() const {
241       return Val.template is<InnerUnion>() &&
242              Val.template get<InnerUnion>().template is<T>();
243     }
244     template <typename T> T get() const {
245       return Val.template get<InnerUnion>().template get<T>();
246     }
247   };
248 
249   struct IsPT3 {
250     ValTy Val;
251     IsPT3(ValTy val) : Val(val) {}
252     template <typename T> int is() const { return Val.template is<T>(); }
253     template <typename T> T get() const { return Val.template get<T>(); }
254   };
255 
256 public:
257   PointerUnion3() = default;
258 
259   PointerUnion3(PT1 V) { Val = InnerUnion(V); }
260   PointerUnion3(PT2 V) { Val = InnerUnion(V); }
261   PointerUnion3(PT3 V) { Val = V; }
262 
263   /// Test if the pointer held in the union is null, regardless of
264   /// which type it is.
265   bool isNull() const { return Val.isNull(); }
266   explicit operator bool() const { return !isNull(); }
267 
268   /// Test if the Union currently holds the type matching T.
269   template <typename T> int is() const {
270     // If T is PT1/PT2 choose IsInnerUnion otherwise choose IsPT3.
271     typedef typename ::llvm::PointerUnionTypeSelector<
272         PT1, T, IsInnerUnion,
273         ::llvm::PointerUnionTypeSelector<PT2, T, IsInnerUnion, IsPT3>>::Return
274         Ty;
275     return Ty(Val).template is<T>();
276   }
277 
278   /// Returns the value of the specified pointer type.
279   ///
280   /// If the specified pointer type is incorrect, assert.
281   template <typename T> T get() const {
282     assert(is<T>() && "Invalid accessor called");
283     // If T is PT1/PT2 choose IsInnerUnion otherwise choose IsPT3.
284     typedef typename ::llvm::PointerUnionTypeSelector<
285         PT1, T, IsInnerUnion,
286         ::llvm::PointerUnionTypeSelector<PT2, T, IsInnerUnion, IsPT3>>::Return
287         Ty;
288     return Ty(Val).template get<T>();
289   }
290 
291   /// Returns the current pointer if it is of the specified pointer type,
292   /// otherwises returns null.
293   template <typename T> T dyn_cast() const {
294     if (is<T>())
295       return get<T>();
296     return T();
297   }
298 
299   /// Assignment from nullptr which just clears the union.
300   const PointerUnion3 &operator=(std::nullptr_t) {
301     Val = nullptr;
302     return *this;
303   }
304 
305   /// Assignment operators - Allow assigning into this union from either
306   /// pointer type, setting the discriminator to remember what it came from.
307   const PointerUnion3 &operator=(const PT1 &RHS) {
308     Val = InnerUnion(RHS);
309     return *this;
310   }
311   const PointerUnion3 &operator=(const PT2 &RHS) {
312     Val = InnerUnion(RHS);
313     return *this;
314   }
315   const PointerUnion3 &operator=(const PT3 &RHS) {
316     Val = RHS;
317     return *this;
318   }
319 
320   void *getOpaqueValue() const { return Val.getOpaqueValue(); }
321   static inline PointerUnion3 getFromOpaqueValue(void *VP) {
322     PointerUnion3 V;
323     V.Val = ValTy::getFromOpaqueValue(VP);
324     return V;
325   }
326 };
327 
328 // Teach SmallPtrSet that PointerUnion3 is "basically a pointer", that has
329 // # low bits available = min(PT1bits,PT2bits,PT2bits)-2.
330 template <typename PT1, typename PT2, typename PT3>
331 class PointerLikeTypeTraits<PointerUnion3<PT1, PT2, PT3>> {
332 public:
333   static inline void *getAsVoidPointer(const PointerUnion3<PT1, PT2, PT3> &P) {
334     return P.getOpaqueValue();
335   }
336 
337   static inline PointerUnion3<PT1, PT2, PT3> getFromVoidPointer(void *P) {
338     return PointerUnion3<PT1, PT2, PT3>::getFromOpaqueValue(P);
339   }
340 
341   // The number of bits available are the min of the two pointer types.
342   enum {
343     NumLowBitsAvailable = PointerLikeTypeTraits<
344         typename PointerUnion3<PT1, PT2, PT3>::ValTy>::NumLowBitsAvailable
345   };
346 };
347 
348 /// A pointer union of four pointer types. See documentation for PointerUnion
349 /// for usage.
350 template <typename PT1, typename PT2, typename PT3, typename PT4>
351 class PointerUnion4 {
352 public:
353   typedef PointerUnion<PT1, PT2> InnerUnion1;
354   typedef PointerUnion<PT3, PT4> InnerUnion2;
355   typedef PointerUnion<InnerUnion1, InnerUnion2> ValTy;
356 
357 private:
358   ValTy Val;
359 
360 public:
361   PointerUnion4() = default;
362 
363   PointerUnion4(PT1 V) { Val = InnerUnion1(V); }
364   PointerUnion4(PT2 V) { Val = InnerUnion1(V); }
365   PointerUnion4(PT3 V) { Val = InnerUnion2(V); }
366   PointerUnion4(PT4 V) { Val = InnerUnion2(V); }
367 
368   /// Test if the pointer held in the union is null, regardless of
369   /// which type it is.
370   bool isNull() const { return Val.isNull(); }
371   explicit operator bool() const { return !isNull(); }
372 
373   /// Test if the Union currently holds the type matching T.
374   template <typename T> int is() const {
375     // If T is PT1/PT2 choose InnerUnion1 otherwise choose InnerUnion2.
376     typedef typename ::llvm::PointerUnionTypeSelector<
377         PT1, T, InnerUnion1, ::llvm::PointerUnionTypeSelector<
378                                  PT2, T, InnerUnion1, InnerUnion2>>::Return Ty;
379     return Val.template is<Ty>() && Val.template get<Ty>().template is<T>();
380   }
381 
382   /// Returns the value of the specified pointer type.
383   ///
384   /// If the specified pointer type is incorrect, assert.
385   template <typename T> T get() const {
386     assert(is<T>() && "Invalid accessor called");
387     // If T is PT1/PT2 choose InnerUnion1 otherwise choose InnerUnion2.
388     typedef typename ::llvm::PointerUnionTypeSelector<
389         PT1, T, InnerUnion1, ::llvm::PointerUnionTypeSelector<
390                                  PT2, T, InnerUnion1, InnerUnion2>>::Return Ty;
391     return Val.template get<Ty>().template get<T>();
392   }
393 
394   /// Returns the current pointer if it is of the specified pointer type,
395   /// otherwises returns null.
396   template <typename T> T dyn_cast() const {
397     if (is<T>())
398       return get<T>();
399     return T();
400   }
401 
402   /// Assignment from nullptr which just clears the union.
403   const PointerUnion4 &operator=(std::nullptr_t) {
404     Val = nullptr;
405     return *this;
406   }
407 
408   /// Assignment operators - Allow assigning into this union from either
409   /// pointer type, setting the discriminator to remember what it came from.
410   const PointerUnion4 &operator=(const PT1 &RHS) {
411     Val = InnerUnion1(RHS);
412     return *this;
413   }
414   const PointerUnion4 &operator=(const PT2 &RHS) {
415     Val = InnerUnion1(RHS);
416     return *this;
417   }
418   const PointerUnion4 &operator=(const PT3 &RHS) {
419     Val = InnerUnion2(RHS);
420     return *this;
421   }
422   const PointerUnion4 &operator=(const PT4 &RHS) {
423     Val = InnerUnion2(RHS);
424     return *this;
425   }
426 
427   void *getOpaqueValue() const { return Val.getOpaqueValue(); }
428   static inline PointerUnion4 getFromOpaqueValue(void *VP) {
429     PointerUnion4 V;
430     V.Val = ValTy::getFromOpaqueValue(VP);
431     return V;
432   }
433 };
434 
435 // Teach SmallPtrSet that PointerUnion4 is "basically a pointer", that has
436 // # low bits available = min(PT1bits,PT2bits,PT2bits)-2.
437 template <typename PT1, typename PT2, typename PT3, typename PT4>
438 class PointerLikeTypeTraits<PointerUnion4<PT1, PT2, PT3, PT4>> {
439 public:
440   static inline void *
441   getAsVoidPointer(const PointerUnion4<PT1, PT2, PT3, PT4> &P) {
442     return P.getOpaqueValue();
443   }
444 
445   static inline PointerUnion4<PT1, PT2, PT3, PT4> getFromVoidPointer(void *P) {
446     return PointerUnion4<PT1, PT2, PT3, PT4>::getFromOpaqueValue(P);
447   }
448 
449   // The number of bits available are the min of the two pointer types.
450   enum {
451     NumLowBitsAvailable = PointerLikeTypeTraits<
452         typename PointerUnion4<PT1, PT2, PT3, PT4>::ValTy>::NumLowBitsAvailable
453   };
454 };
455 
456 // Teach DenseMap how to use PointerUnions as keys.
457 template <typename T, typename U> struct DenseMapInfo<PointerUnion<T, U>> {
458   typedef PointerUnion<T, U> Pair;
459   typedef DenseMapInfo<T> FirstInfo;
460   typedef DenseMapInfo<U> SecondInfo;
461 
462   static inline Pair getEmptyKey() { return Pair(FirstInfo::getEmptyKey()); }
463   static inline Pair getTombstoneKey() {
464     return Pair(FirstInfo::getTombstoneKey());
465   }
466   static unsigned getHashValue(const Pair &PairVal) {
467     intptr_t key = (intptr_t)PairVal.getOpaqueValue();
468     return DenseMapInfo<intptr_t>::getHashValue(key);
469   }
470   static bool isEqual(const Pair &LHS, const Pair &RHS) {
471     return LHS.template is<T>() == RHS.template is<T>() &&
472            (LHS.template is<T>() ? FirstInfo::isEqual(LHS.template get<T>(),
473                                                       RHS.template get<T>())
474                                  : SecondInfo::isEqual(LHS.template get<U>(),
475                                                        RHS.template get<U>()));
476   }
477 };
478 
479 } // end namespace llvm
480 
481 #endif // LLVM_ADT_POINTERUNION_H
482