move my_assume_aligned() to a separate header

include/assume_aligned.h

@@ -0,0 +1,70 @@
+/*
+   Copyright (c) 2000, 2012, Oracle and/or its affiliates.
+   Copyright (c) 2020, MariaDB Corporation.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */
+
+#pragma once
+
+#include <cassert>
+#include <cstring>
+
+#ifdef _MSC_VER
+template <std::size_t Alignment, class T>
+static inline T my_assume_aligned(T ptr)
+{
+  assert(reinterpret_cast<size_t>(ptr) % Alignment == 0);
+  __assume(reinterpret_cast<size_t>(ptr) % Alignment == 0);
+  return ptr;
+}
+#else
+template <std::size_t Alignment, class T>
+static inline T my_assume_aligned(T ptr)
+{
+  assert(reinterpret_cast<size_t>(ptr) % Alignment == 0);
+  return static_cast<T>(__builtin_assume_aligned(ptr, Alignment));
+}
+#endif
+
+template <std::size_t Alignment>
+inline void *memcpy_aligned(void *dest, const void *src, size_t n)
+{
+  static_assert(Alignment && !(Alignment & (Alignment - 1)), "power of 2");
+
+  return std::memcpy(my_assume_aligned<Alignment>(dest),
+                     my_assume_aligned<Alignment>(src), n);
+}
+template <std::size_t Alignment>
+inline void *memmove_aligned(void *dest, const void *src, size_t n)
+{
+  static_assert(Alignment && !(Alignment & (Alignment - 1)), "power of 2");
+
+  return std::memmove(my_assume_aligned<Alignment>(dest),
+                      my_assume_aligned<Alignment>(src), n);
+}
+template <std::size_t Alignment>
+inline int memcmp_aligned(const void *s1, const void *s2, size_t n)
+{
+  static_assert(Alignment && !(Alignment & (Alignment - 1)), "power of 2");
+
+  return std::memcmp(my_assume_aligned<Alignment>(s1),
+                     my_assume_aligned<Alignment>(s2), n);
+}
+template <std::size_t Alignment>
+inline void *memset_aligned(void *s, int c, size_t n)
+{
+  static_assert(Alignment && !(Alignment & (Alignment - 1)), "power of 2");
+
+  return std::memset(my_assume_aligned<Alignment>(s), c, n);
+}