LLVM  10.0.0svn
PointerLikeTypeTraits.h
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1 //===- llvm/Support/PointerLikeTypeTraits.h - Pointer Traits ----*- 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 PointerLikeTypeTraits class. This allows data
10 // structures to reason about pointers and other things that are pointer sized.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_SUPPORT_POINTERLIKETYPETRAITS_H
15 #define LLVM_SUPPORT_POINTERLIKETYPETRAITS_H
16 
17 #include "llvm/Support/DataTypes.h"
18 #include <assert.h>
19 #include <type_traits>
20 
21 namespace llvm {
22 
23 /// A traits type that is used to handle pointer types and things that are just
24 /// wrappers for pointers as a uniform entity.
25 template <typename T> struct PointerLikeTypeTraits;
26 
27 namespace detail {
28 /// A tiny meta function to compute the log2 of a compile time constant.
29 template <size_t N>
31  : std::integral_constant<size_t, ConstantLog2<N / 2>::value + 1> {};
32 template <> struct ConstantLog2<1> : std::integral_constant<size_t, 0> {};
33 
34 // Provide a trait to check if T is pointer-like.
35 template <typename T, typename U = void> struct HasPointerLikeTypeTraits {
36  static const bool value = false;
37 };
38 
39 // sizeof(T) is valid only for a complete T.
40 template <typename T> struct HasPointerLikeTypeTraits<
41  T, decltype((sizeof(PointerLikeTypeTraits<T>) + sizeof(T)), void())> {
42  static const bool value = true;
43 };
44 
45 template <typename T> struct IsPointerLike {
46  static const bool value = HasPointerLikeTypeTraits<T>::value;
47 };
48 
49 template <typename T> struct IsPointerLike<T *> {
50  static const bool value = true;
51 };
52 } // namespace detail
53 
54 // Provide PointerLikeTypeTraits for non-cvr pointers.
55 template <typename T> struct PointerLikeTypeTraits<T *> {
56  static inline void *getAsVoidPointer(T *P) { return P; }
57  static inline T *getFromVoidPointer(void *P) { return static_cast<T *>(P); }
58 
59  enum { NumLowBitsAvailable = detail::ConstantLog2<alignof(T)>::value };
60 };
61 
62 template <> struct PointerLikeTypeTraits<void *> {
63  static inline void *getAsVoidPointer(void *P) { return P; }
64  static inline void *getFromVoidPointer(void *P) { return P; }
65 
66  /// Note, we assume here that void* is related to raw malloc'ed memory and
67  /// that malloc returns objects at least 4-byte aligned. However, this may be
68  /// wrong, or pointers may be from something other than malloc. In this case,
69  /// you should specify a real typed pointer or avoid this template.
70  ///
71  /// All clients should use assertions to do a run-time check to ensure that
72  /// this is actually true.
73  enum { NumLowBitsAvailable = 2 };
74 };
75 
76 // Provide PointerLikeTypeTraits for const things.
77 template <typename T> struct PointerLikeTypeTraits<const T> {
79 
80  static inline const void *getAsVoidPointer(const T P) {
81  return NonConst::getAsVoidPointer(P);
82  }
83  static inline const T getFromVoidPointer(const void *P) {
84  return NonConst::getFromVoidPointer(const_cast<void *>(P));
85  }
86  enum { NumLowBitsAvailable = NonConst::NumLowBitsAvailable };
87 };
88 
89 // Provide PointerLikeTypeTraits for const pointers.
90 template <typename T> struct PointerLikeTypeTraits<const T *> {
92 
93  static inline const void *getAsVoidPointer(const T *P) {
94  return NonConst::getAsVoidPointer(const_cast<T *>(P));
95  }
96  static inline const T *getFromVoidPointer(const void *P) {
97  return NonConst::getFromVoidPointer(const_cast<void *>(P));
98  }
99  enum { NumLowBitsAvailable = NonConst::NumLowBitsAvailable };
100 };
101 
102 // Provide PointerLikeTypeTraits for uintptr_t.
103 template <> struct PointerLikeTypeTraits<uintptr_t> {
104  static inline void *getAsVoidPointer(uintptr_t P) {
105  return reinterpret_cast<void *>(P);
106  }
107  static inline uintptr_t getFromVoidPointer(void *P) {
108  return reinterpret_cast<uintptr_t>(P);
109  }
110  // No bits are available!
111  enum { NumLowBitsAvailable = 0 };
112 };
113 
114 /// Provide suitable custom traits struct for function pointers.
115 ///
116 /// Function pointers can't be directly given these traits as functions can't
117 /// have their alignment computed with `alignof` and we need different casting.
118 ///
119 /// To rely on higher alignment for a specialized use, you can provide a
120 /// customized form of this template explicitly with higher alignment, and
121 /// potentially use alignment attributes on functions to satisfy that.
122 template <int Alignment, typename FunctionPointerT>
124  enum { NumLowBitsAvailable = detail::ConstantLog2<Alignment>::value };
125  static inline void *getAsVoidPointer(FunctionPointerT P) {
126  assert((reinterpret_cast<uintptr_t>(P) &
127  ~((uintptr_t)-1 << NumLowBitsAvailable)) == 0 &&
128  "Alignment not satisfied for an actual function pointer!");
129  return reinterpret_cast<void *>(P);
130  }
131  static inline FunctionPointerT getFromVoidPointer(void *P) {
132  return reinterpret_cast<FunctionPointerT>(P);
133  }
134 };
135 
136 /// Provide a default specialization for function pointers that assumes 4-byte
137 /// alignment.
138 ///
139 /// We assume here that functions used with this are always at least 4-byte
140 /// aligned. This means that, for example, thumb functions won't work or systems
141 /// with weird unaligned function pointers won't work. But all practical systems
142 /// we support satisfy this requirement.
143 template <typename ReturnT, typename... ParamTs>
144 struct PointerLikeTypeTraits<ReturnT (*)(ParamTs...)>
145  : FunctionPointerLikeTypeTraits<4, ReturnT (*)(ParamTs...)> {};
146 
147 } // end namespace llvm
148 
149 #endif
This class represents lattice values for constants.
Definition: AllocatorList.h:23
static void * getAsVoidPointer(FunctionPointerT P)
A tiny meta function to compute the log2 of a compile time constant.
A traits type that is used to handle pointer types and things that are just wrappers for pointers as ...
static const T * getFromVoidPointer(const void *P)
static const void * getAsVoidPointer(const T *P)
#define P(N)
Provide suitable custom traits struct for function pointers.
static FunctionPointerT getFromVoidPointer(void *P)
static const T getFromVoidPointer(const void *P)
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
static const void * getAsVoidPointer(const T P)
aarch64 promote const