PointerLikeTypeTraits.h revision 355940
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