[libc++] Move the definition of aligned allocation helpers outside of <new>

They are not needed in <new> -- in fact they are only needed in .cpp files.
Getting those out of the way makes the headers smaller and also makes it
easier to use the library on platforms where aligned allocation is not
available.

Differential Revision: https://reviews.llvm.org/D139231

1 files changed, 66 insertions, 0 deletions

diff --git a/libcxx/include/__memory/aligned_alloc.h b/libcxx/include/__memory/aligned_alloc.h
new file mode 100644
index 000000000000..41520cffaa46
--- /dev/null
+++ b/libcxx/include/__memory/aligned_alloc.h
@@ -0,0 +1,66 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___MEMORY_ALIGNED_ALLOC_H
+#define _LIBCPP___MEMORY_ALIGNED_ALLOC_H
+
+#include <__config>
+#include <cstddef>
+#include <cstdlib>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#ifndef _LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION
+
+// Low-level helpers to call the aligned allocation and deallocation functions
+// on the target platform. This is used to implement libc++'s own memory
+// allocation routines -- if you need to allocate memory inside the library,
+// chances are that you want to use `__libcpp_allocate` instead.
+//
+// Returns the allocated memory, or `nullptr` on failure.
+inline _LIBCPP_HIDE_FROM_ABI
+void* __libcpp_aligned_alloc(std::size_t __alignment, std::size_t __size) {
+#  if defined(_LIBCPP_MSVCRT_LIKE)
+    return ::_aligned_malloc(__size, __alignment);
+#  elif _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_C11_ALIGNED_ALLOC)
+    // aligned_alloc() requires that __size is a multiple of __alignment,
+    // but for C++ [new.delete.general], only states "if the value of an
+    // alignment argument passed to any of these functions is not a valid
+    // alignment value, the behavior is undefined".
+    // To handle calls such as ::operator new(1, std::align_val_t(128)), we
+    // round __size up to the next multiple of __alignment.
+    size_t __rounded_size = (__size + __alignment - 1) & ~(__alignment - 1);
+    // Rounding up could have wrapped around to zero, so we have to add another
+    // max() ternary to the actual call site to avoid succeeded in that case.
+    return ::aligned_alloc(__alignment, __size > __rounded_size ? __size : __rounded_size);
+#  else
+    void* __result = nullptr;
+    (void)::posix_memalign(&__result, __alignment, __size);
+    // If posix_memalign fails, __result is unmodified so we still return `nullptr`.
+    return __result;
+#  endif
+}
+
+inline _LIBCPP_HIDE_FROM_ABI
+void __libcpp_aligned_free(void* __ptr) {
+#if defined(_LIBCPP_MSVCRT_LIKE)
+  ::_aligned_free(__ptr);
+#else
+  ::free(__ptr);
+#endif
+}
+
+#endif // !_LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___MEMORY_ALIGNED_ALLOC_H