| //===- llvm/Support/PointerLikeTypeTraits.h - Pointer Traits ----*- C++ -*-===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file defines the PointerLikeTypeTraits class. This allows data |
| // structures to reason about pointers and other things that are pointer sized. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLVM_SUPPORT_POINTERLIKETYPETRAITS_H |
| #define LLVM_SUPPORT_POINTERLIKETYPETRAITS_H |
| |
| #include "llvm/Support/DataTypes.h" |
| #include <cassert> |
| #include <type_traits> |
| |
| namespace llvm { |
| |
| /// A traits type that is used to handle pointer types and things that are just |
| /// wrappers for pointers as a uniform entity. |
| template <typename T> struct PointerLikeTypeTraits; |
| |
| namespace detail { |
| /// A tiny meta function to compute the log2 of a compile time constant. |
| template <size_t N> |
| struct ConstantLog2 |
| : std::integral_constant<size_t, ConstantLog2<N / 2>::value + 1> {}; |
| template <> struct ConstantLog2<1> : std::integral_constant<size_t, 0> {}; |
| |
| // Provide a trait to check if T is pointer-like. |
| template <typename T, typename U = void> struct HasPointerLikeTypeTraits { |
| static const bool value = false; |
| }; |
| |
| // sizeof(T) is valid only for a complete T. |
| template <typename T> |
| struct HasPointerLikeTypeTraits< |
| T, decltype((sizeof(PointerLikeTypeTraits<T>) + sizeof(T)), void())> { |
| static const bool value = true; |
| }; |
| |
| template <typename T> struct IsPointerLike { |
| static const bool value = HasPointerLikeTypeTraits<T>::value; |
| }; |
| |
| template <typename T> struct IsPointerLike<T *> { |
| static const bool value = true; |
| }; |
| } // namespace detail |
| |
| // Provide PointerLikeTypeTraits for non-cvr pointers. |
| template <typename T> struct PointerLikeTypeTraits<T *> { |
| static inline void *getAsVoidPointer(T *P) { return P; } |
| static inline T *getFromVoidPointer(void *P) { return static_cast<T *>(P); } |
| |
| static constexpr int NumLowBitsAvailable = |
| detail::ConstantLog2<alignof(T)>::value; |
| }; |
| |
| template <> struct PointerLikeTypeTraits<void *> { |
| static inline void *getAsVoidPointer(void *P) { return P; } |
| static inline void *getFromVoidPointer(void *P) { return P; } |
| |
| /// Note, we assume here that void* is related to raw malloc'ed memory and |
| /// that malloc returns objects at least 4-byte aligned. However, this may be |
| /// wrong, or pointers may be from something other than malloc. In this case, |
| /// you should specify a real typed pointer or avoid this template. |
| /// |
| /// All clients should use assertions to do a run-time check to ensure that |
| /// this is actually true. |
| static constexpr int NumLowBitsAvailable = 2; |
| }; |
| |
| // Provide PointerLikeTypeTraits for const things. |
| template <typename T> struct PointerLikeTypeTraits<const T> { |
| typedef PointerLikeTypeTraits<T> NonConst; |
| |
| static inline const void *getAsVoidPointer(const T P) { |
| return NonConst::getAsVoidPointer(P); |
| } |
| static inline const T getFromVoidPointer(const void *P) { |
| return NonConst::getFromVoidPointer(const_cast<void *>(P)); |
| } |
| static constexpr int NumLowBitsAvailable = NonConst::NumLowBitsAvailable; |
| }; |
| |
| // Provide PointerLikeTypeTraits for const pointers. |
| template <typename T> struct PointerLikeTypeTraits<const T *> { |
| typedef PointerLikeTypeTraits<T *> NonConst; |
| |
| static inline const void *getAsVoidPointer(const T *P) { |
| return NonConst::getAsVoidPointer(const_cast<T *>(P)); |
| } |
| static inline const T *getFromVoidPointer(const void *P) { |
| return NonConst::getFromVoidPointer(const_cast<void *>(P)); |
| } |
| static constexpr int NumLowBitsAvailable = NonConst::NumLowBitsAvailable; |
| }; |
| |
| // Provide PointerLikeTypeTraits for uintptr_t. |
| template <> struct PointerLikeTypeTraits<uintptr_t> { |
| static inline void *getAsVoidPointer(uintptr_t P) { |
| return reinterpret_cast<void *>(P); |
| } |
| static inline uintptr_t getFromVoidPointer(void *P) { |
| return reinterpret_cast<uintptr_t>(P); |
| } |
| // No bits are available! |
| static constexpr int NumLowBitsAvailable = 0; |
| }; |
| |
| /// Provide suitable custom traits struct for function pointers. |
| /// |
| /// Function pointers can't be directly given these traits as functions can't |
| /// have their alignment computed with `alignof` and we need different casting. |
| /// |
| /// To rely on higher alignment for a specialized use, you can provide a |
| /// customized form of this template explicitly with higher alignment, and |
| /// potentially use alignment attributes on functions to satisfy that. |
| template <int Alignment, typename FunctionPointerT> |
| struct FunctionPointerLikeTypeTraits { |
| static constexpr int NumLowBitsAvailable = |
| detail::ConstantLog2<Alignment>::value; |
| static inline void *getAsVoidPointer(FunctionPointerT P) { |
| assert((reinterpret_cast<uintptr_t>(P) & |
| ~((uintptr_t)-1 << NumLowBitsAvailable)) == 0 && |
| "Alignment not satisfied for an actual function pointer!"); |
| return reinterpret_cast<void *>(P); |
| } |
| static inline FunctionPointerT getFromVoidPointer(void *P) { |
| return reinterpret_cast<FunctionPointerT>(P); |
| } |
| }; |
| |
| /// Provide a default specialization for function pointers that assumes 4-byte |
| /// alignment. |
| /// |
| /// We assume here that functions used with this are always at least 4-byte |
| /// aligned. This means that, for example, thumb functions won't work or systems |
| /// with weird unaligned function pointers won't work. But all practical systems |
| /// we support satisfy this requirement. |
| template <typename ReturnT, typename... ParamTs> |
| struct PointerLikeTypeTraits<ReturnT (*)(ParamTs...)> |
| : FunctionPointerLikeTypeTraits<4, ReturnT (*)(ParamTs...)> {}; |
| |
| } // end namespace llvm |
| |
| #endif |