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
21namespace 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.
25template <typename T> struct PointerLikeTypeTraits;
26
27namespace detail {
28/// A tiny meta function to compute the log2 of a compile time constant.
29template <size_t N>
30struct ConstantLog2
31 : std::integral_constant<size_t, ConstantLog2<N / 2>::value + 1> {};
32template <> struct ConstantLog2<1> : std::integral_constant<size_t, 0> {};
33
34// Provide a trait to check if T is pointer-like.
35template <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.
40template <typename T> struct HasPointerLikeTypeTraits<
41 T, decltype((sizeof(PointerLikeTypeTraits<T>) + sizeof(T)), void())> {
42 static const bool value = true;
43};
44
45template <typename T> struct IsPointerLike {
46 static const bool value = HasPointerLikeTypeTraits<T>::value;
47};
48
49template <typename T> struct IsPointerLike<T *> {
50 static const bool value = true;
51};
52} // namespace detail
53
54// Provide PointerLikeTypeTraits for non-cvr pointers.
55template <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
62template <> 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.
77template <typename T> struct PointerLikeTypeTraits<const T> {
78 typedef PointerLikeTypeTraits<T> NonConst;
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.
90template <typename T> struct PointerLikeTypeTraits<const T *> {
91 typedef PointerLikeTypeTraits<T *> NonConst;
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.
103template <> 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.
122template <int Alignment, typename FunctionPointerT>
123struct FunctionPointerLikeTypeTraits {
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.
143template <typename ReturnT, typename... ParamTs>
144struct PointerLikeTypeTraits<ReturnT (*)(ParamTs...)>
145 : FunctionPointerLikeTypeTraits<4, ReturnT (*)(ParamTs...)> {};
146
147} // end namespace llvm
148
149#endif
150