[PATCH] Split std::align/assume_aligned to bits/align.h

[PATCH] Split std::align/assume_aligned to bits/align.h

[Thomas Rodgers]

We would like to be able to use these things without having to pull in
the whole of <memory>.

        * include/Makefile.am (bits_headers): Add new header.
	* include/Makefile.in: Regenerate.
        * include/bits/align.h: New file.
        * include/std/memory (align): Move definition to bits/align.h.
        (assume_aligned): Likewise.
---
 libstdc++-v3/include/Makefile.am  |   1 +
 libstdc++-v3/include/Makefile.in  |   1 +
 libstdc++-v3/include/bits/align.h | 104 ++++++++++++++++++++++++++++++
 libstdc++-v3/include/std/memory   |  60 +----------------
 4 files changed, 107 insertions(+), 59 deletions(-)
 create mode 100644 libstdc++-v3/include/bits/align.h

diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
index bae97852348..eabec88219d 100644
--- a/libstdc++-v3/include/Makefile.am
+++ b/libstdc++-v3/include/Makefile.am
@@ -99,6 +99,7 @@ bits_srcdir = ${glibcxx_srcdir}/include/bits
 bits_builddir = ./bits
 bits_headers = \
 	${bits_srcdir}/algorithmfwd.h \
+	${bits_srcdir}/align.h \
 	${bits_srcdir}/alloc_traits.h \
 	${bits_srcdir}/allocated_ptr.h \
 	${bits_srcdir}/allocator.h \
diff --git a/libstdc++-v3/include/bits/align.h b/libstdc++-v3/include/bits/align.h
new file mode 100644
index 00000000000..593b337f897
--- /dev/null
+++ b/libstdc++-v3/include/bits/align.h
@@ -0,0 +1,104 @@
+// align implementation -*- C++ -*-
+
+// Copyright (C) 2008-2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library 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; either version 3, or (at your option)
+// any later version.
+
+// This library 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.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+// <http://www.gnu.org/licenses/>.
+
+/** @file bits/align.h
+ *  This is an internal header file, included by other library headers.
+ *  Do not attempt to use it directly. @headername{memory}
+ */
+
+#ifndef _ALIGN_H
+#define _ALIGN_H 1
+
+#include <bits/c++config.h>
+
+#include <bit>          // std::has_single_bit
+#include <stdint.h>     // uintptr_t
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+/**
+ *  @brief Fit aligned storage in buffer.
+ *  @ingroup memory
+ *
+ *  This function tries to fit @a __size bytes of storage with alignment
+ *  @a __align into the buffer @a __ptr of size @a __space bytes.  If such
+ *  a buffer fits then @a __ptr is changed to point to the first byte of the
+ *  aligned storage and @a __space is reduced by the bytes used for alignment.
+ *
+ *  C++11 20.6.5 [ptr.align]
+ *
+ *  @param __align   A fundamental or extended alignment value.
+ *  @param __size    Size of the aligned storage required.
+ *  @param __ptr     Pointer to a buffer of @a __space bytes.
+ *  @param __space   Size of the buffer pointed to by @a __ptr.
+ *  @return the updated pointer if the aligned storage fits, otherwise nullptr.
+ *
+ */
+inline void*
+align(size_t __align, size_t __size, void*& __ptr, size_t& __space) noexcept
+{
+#ifdef _GLIBCXX_USE_C99_STDINT_TR1
+  const auto __intptr = reinterpret_cast<uintptr_t>(__ptr);
+#else
+  // Cannot use std::uintptr_t so assume that std::size_t can be used instead.
+  static_assert(sizeof(size_t) >= sizeof(void*),
+      "std::size_t must be a suitable substitute for std::uintptr_t");
+  const auto __intptr = reinterpret_cast<unsigned long long>(__ptr);
+#endif
+  const auto __aligned = (__intptr - 1u + __align) & -__align;
+  const auto __diff = __aligned - __intptr;
+  if ((__size + __diff) > __space)
+    return nullptr;
+  else
+    {
+      __space -= __diff;
+      return __ptr = reinterpret_cast<void*>(__aligned);
+    }
+}
+
+#if __cplusplus > 201703L
+#define __cpp_lib_assume_aligned 201811L
+  /** @brief Inform the compiler that a pointer is aligned.
+   *
+   *  @tparam _Align An alignment value (i.e. a power of two)
+   *  @tparam _Tp    An object type
+   *  @param  __ptr  A pointer that is aligned to _Align
+   *  @ingroup memory
+   */
+  template<size_t _Align, class _Tp>
+    [[nodiscard,__gnu__::__always_inline__]]
+    constexpr _Tp* assume_aligned(_Tp* __ptr)
+    {
+      static_assert(std::has_single_bit(_Align));
+      _GLIBCXX_DEBUG_ASSERT((std::uintptr_t)__ptr % _Align == 0);
+      return static_cast<_Tp*>(__builtin_assume_aligned(__ptr, _Align));
+    }
+#endif // C++2a
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace
+
+#endif /* _ALIGN_H */
diff --git a/libstdc++-v3/include/std/memory b/libstdc++-v3/include/std/memory
index 1e8eebd731c..a56952fb114 100644
--- a/libstdc++-v3/include/std/memory
+++ b/libstdc++-v3/include/std/memory
@@ -61,6 +61,7 @@
  */
 
 #include <bits/stl_algobase.h>
+#include <bits/align.h>
 #include <bits/allocator.h>
 #include <bits/stl_construct.h>
 #include <bits/stl_uninitialized.h>
@@ -101,46 +102,6 @@ namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
-/**
- *  @brief Fit aligned storage in buffer.
- *  @ingroup memory
- *
- *  This function tries to fit @a __size bytes of storage with alignment
- *  @a __align into the buffer @a __ptr of size @a __space bytes.  If such
- *  a buffer fits then @a __ptr is changed to point to the first byte of the
- *  aligned storage and @a __space is reduced by the bytes used for alignment.
- *
- *  C++11 20.6.5 [ptr.align]
- *
- *  @param __align   A fundamental or extended alignment value.
- *  @param __size    Size of the aligned storage required.
- *  @param __ptr     Pointer to a buffer of @a __space bytes.
- *  @param __space   Size of the buffer pointed to by @a __ptr.
- *  @return the updated pointer if the aligned storage fits, otherwise nullptr.
- *
- */
-inline void*
-align(size_t __align, size_t __size, void*& __ptr, size_t& __space) noexcept
-{
-#ifdef _GLIBCXX_USE_C99_STDINT_TR1
-  const auto __intptr = reinterpret_cast<uintptr_t>(__ptr);
-#else
-  // Cannot use std::uintptr_t so assume that std::size_t can be used instead.
-  static_assert(sizeof(size_t) >= sizeof(void*),
-      "std::size_t must be a suitable substitute for std::uintptr_t");
-  const auto __intptr = reinterpret_cast<unsigned long long>(__ptr);
-#endif
-  const auto __aligned = (__intptr - 1u + __align) & -__align;
-  const auto __diff = __aligned - __intptr;
-  if ((__size + __diff) > __space)
-    return nullptr;
-  else
-    {
-      __space -= __diff;
-      return __ptr = reinterpret_cast<void*>(__aligned);
-    }
-}
-
 /** @defgroup ptr_safety Pointer Safety and Garbage Collection
  *  @ingroup memory
  *
@@ -179,25 +140,6 @@ inline pointer_safety
 get_pointer_safety() noexcept { return pointer_safety::relaxed; }
 // @}
 
-#if __cplusplus > 201703L
-#define __cpp_lib_assume_aligned 201811L
-  /** @brief Inform the compiler that a pointer is aligned.
-   *
-   *  @tparam _Align An alignment value (i.e. a power of two)
-   *  @tparam _Tp    An object type
-   *  @param  __ptr  A pointer that is aligned to _Align
-   *  @ingroup memory
-   */
-  template<size_t _Align, class _Tp>
-    [[nodiscard,__gnu__::__always_inline__]]
-    constexpr _Tp* assume_aligned(_Tp* __ptr)
-    {
-      static_assert(std::has_single_bit(_Align));
-      _GLIBCXX_DEBUG_ASSERT((std::uintptr_t)__ptr % _Align == 0);
-      return static_cast<_Tp*>(__builtin_assume_aligned(__ptr, _Align));
-    }
-#endif // C++2a
-
 #if __cplusplus > 201703L
   template<typename _Tp>
     struct __is_pair : false_type { };
-- 
2.26.2

Re: [PATCH] Split std::align/assume_aligned to bits/align.h

[Jonathan Wakely]

On 09/09/20 17:38 -0700, Thomas Rodgers wrote:
>We would like to be able to use these things without having to pull in
>the whole of <memory>.
>
>        * include/Makefile.am (bits_headers): Add new header.
>	* include/Makefile.in: Regenerate.
>        * include/bits/align.h: New file.
>        * include/std/memory (align): Move definition to bits/align.h.
>        (assume_aligned): Likewise.
>---
> libstdc++-v3/include/Makefile.am  |   1 +
> libstdc++-v3/include/Makefile.in  |   1 +
> libstdc++-v3/include/bits/align.h | 104 ++++++++++++++++++++++++++++++
> libstdc++-v3/include/std/memory   |  60 +----------------
> 4 files changed, 107 insertions(+), 59 deletions(-)
> create mode 100644 libstdc++-v3/include/bits/align.h
>
>diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
>index bae97852348..eabec88219d 100644
>--- a/libstdc++-v3/include/Makefile.am
>+++ b/libstdc++-v3/include/Makefile.am
>@@ -99,6 +99,7 @@ bits_srcdir = ${glibcxx_srcdir}/include/bits
> bits_builddir = ./bits
> bits_headers = \
> 	${bits_srcdir}/algorithmfwd.h \
>+	${bits_srcdir}/align.h \
> 	${bits_srcdir}/alloc_traits.h \
> 	${bits_srcdir}/allocated_ptr.h \
> 	${bits_srcdir}/allocator.h \
>diff --git a/libstdc++-v3/include/bits/align.h b/libstdc++-v3/include/bits/align.h
>new file mode 100644
>index 00000000000..593b337f897
>--- /dev/null
>+++ b/libstdc++-v3/include/bits/align.h
>@@ -0,0 +1,104 @@
>+// align implementation -*- C++ -*-
>+
>+// Copyright (C) 2008-2020 Free Software Foundation, Inc.

std::align was added in 2014 by
2f6ca9d31799133f80e446bd1faad5d9a67bac00 so that should be the first
date in the new file.

>+//
>+// This file is part of the GNU ISO C++ Library.  This library 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; either version 3, or (at your option)
>+// any later version.
>+
>+// This library 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.
>+
>+// Under Section 7 of GPL version 3, you are granted additional
>+// permissions described in the GCC Runtime Library Exception, version
>+// 3.1, as published by the Free Software Foundation.
>+
>+// You should have received a copy of the GNU General Public License and
>+// a copy of the GCC Runtime Library Exception along with this program;
>+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
>+// <http://www.gnu.org/licenses/>.
>+
>+/** @file bits/align.h
>+ *  This is an internal header file, included by other library headers.
>+ *  Do not attempt to use it directly. @headername{memory}
>+ */
>+
>+#ifndef _ALIGN_H
>+#define _ALIGN_H 1

I'm a little worried this macro isn't unique enough and will clash
with something. Please use _GLIBCXX_ALIGN_H for the header guard
macro.

>+
>+#include <bits/c++config.h>
>+
>+#include <bit>          // std::has_single_bit
>+#include <stdint.h>     // uintptr_t
>+
>+namespace std _GLIBCXX_VISIBILITY(default)
>+{
>+_GLIBCXX_BEGIN_NAMESPACE_VERSION
>+
>+/**
>+ *  @brief Fit aligned storage in buffer.
>+ *  @ingroup memory
>+ *
>+ *  This function tries to fit @a __size bytes of storage with alignment
>+ *  @a __align into the buffer @a __ptr of size @a __space bytes.  If such
>+ *  a buffer fits then @a __ptr is changed to point to the first byte of the
>+ *  aligned storage and @a __space is reduced by the bytes used for alignment.
>+ *
>+ *  C++11 20.6.5 [ptr.align]
>+ *
>+ *  @param __align   A fundamental or extended alignment value.
>+ *  @param __size    Size of the aligned storage required.
>+ *  @param __ptr     Pointer to a buffer of @a __space bytes.
>+ *  @param __space   Size of the buffer pointed to by @a __ptr.
>+ *  @return the updated pointer if the aligned storage fits, otherwise nullptr.
>+ *
>+ */
>+inline void*
>+align(size_t __align, size_t __size, void*& __ptr, size_t& __space) noexcept
>+{
>+#ifdef _GLIBCXX_USE_C99_STDINT_TR1
>+  const auto __intptr = reinterpret_cast<uintptr_t>(__ptr);
>+#else
>+  // Cannot use std::uintptr_t so assume that std::size_t can be used instead.
>+  static_assert(sizeof(size_t) >= sizeof(void*),
>+      "std::size_t must be a suitable substitute for std::uintptr_t");
>+  const auto __intptr = reinterpret_cast<unsigned long long>(__ptr);

Why on earth did I check that we can use size_t ... and then not use
size_t?! Not your problem though, that can be fixed separately.

OK for trunk with the copyright year and header guard changes, thanks!

[PATCH] libstdc++: only pull in bits/align.h if C++11 or later

[Thomas Rodgers]

From: Thomas Rodgers <trodgers@redhat.com>

libstdc++-v3/ChangeLog:

	* include/std/memory: Move #include <bits/align.h> inside C++11
	conditional includes.

Tested x86_64-pc-linux-gnu, committed to master.

---
 libstdc++-v3/include/std/memory | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/memory b/libstdc++-v3/include/std/memory
index a56952fb114..aee7b050bd7 100644
--- a/libstdc++-v3/include/std/memory
+++ b/libstdc++-v3/include/std/memory
@@ -61,7 +61,6 @@
  */
 
 #include <bits/stl_algobase.h>
-#include <bits/align.h>
 #include <bits/allocator.h>
 #include <bits/stl_construct.h>
 #include <bits/stl_uninitialized.h>
@@ -75,6 +74,7 @@
 #  include <iosfwd>           	  // std::basic_ostream
 #  include <ext/atomicity.h>
 #  include <ext/concurrence.h>
+#  include <bits/align.h>
 #  include <bits/functexcept.h>
 #  include <bits/stl_function.h>  // std::less
 #  include <bits/uses_allocator.h>
-- 
2.26.2