Alignment.hpp

// Copyright (c) 2019 Graphcore Ltd. All rights reserved.
 
#ifndef poplar_Alignment_hpp
#define poplar_Alignment_hpp
 
#include <cstddef>
 
// This is a replacement for __attribute__((assume_aligned(N))) as it can more
// reliably generate alignment assumptions at the IR level after the following
// clang patches:
// * https://reviews.llvm.org/D73005
// * https://reviews.llvm.org/D73006
//
// Also see T17070.
//
// This function has the same interface as std::assume_aligned (C++20), making
// a future transition for the standard function easier.
//
// Based on proposed implementation here:
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1007r1.pdf
//
// Extend this for other platforms and compilers as needed (see link above).
template <std::size_t N, typename T>
#if defined(__clang__) || defined(__GNUC__)
__attribute__((always_inline))
#endif
constexpr T *
poplar_assume_aligned(T *ptr) noexcept {
#if defined(__clang__) || defined(__GNUC__)
  return reinterpret_cast<T *>(__builtin_assume_aligned(ptr, N));
#else
  return ptr;
#endif
}
 
#endif // poplar_Alignment_hpp