[PATCH] libstdc++: Remove broken std::allocator base classes [PR103340]

[PATCH] libstdc++: Remove broken std::allocator base classes [PR103340]

[Jonathan Wakely]

I plan to commit this Real Soon. Please yell if you need these
alternative std::allocator back-ends to stay (and explain how you're
using them when they've  been broken for years, and start sending test
results to the gcc-testresults mailing list, and ideally offer to
maintain them).

Tested powerpc64le-linux.

=== 8< === 8< === 8< ===

The bitmap_allocator, __mt_alloc and __pool_alloc extensions are no
longer suitable for use as the base class of std::allocator, because
they have not been updated to meet the C++20 requirements.  There is a
patch attached to PR 103340 which addresses that, but more work would be
needed to solve the linking errors that occur when the library is
configured to use them.

Using --enable-libstdcxx-allocator=bitmap wouldn't even bootstrap for
the past few years, and I can't find any gcc-testresults reports using
any of these allocators. This patch removes the configure option to use
these are the std::allocator base class. The allocators are still in the
tree and can be used directly, you just can't configure the library to
use one of them as the base class of std::allocator.

libstdc++-v3/ChangeLog:

	PR libstdc++/103340
	PR libstdc++/103400
	PR libstdc++/103381
	* acinclude.m4 (GLIBCXX_ENABLE_ALLOCATOR): Remove mt, bitmap
	and pool options.
	* configure: Regenerate.
	* doc/xml/manual/allocator.xml: Update.
	* doc/xml/manual/configure.xml: Update.
	* doc/xml/manual/evolution.xml: Document removal.
	* doc/xml/manual/mt_allocator.xml: Editorial tweaks.
	* doc/html/manual/*: Regenerate.
---
 libstdc++-v3/acinclude.m4                     | 14 +---
 libstdc++-v3/configure                        | 14 +---
 libstdc++-v3/doc/html/manual/api.html         |  3 +
 libstdc++-v3/doc/html/manual/configure.html   | 10 ++-
 libstdc++-v3/doc/html/manual/memory.html      | 57 +++++-----------
 .../doc/html/manual/mt_allocator.html         |  8 +--
 libstdc++-v3/doc/xml/manual/allocator.xml     | 67 ++++++-------------
 libstdc++-v3/doc/xml/manual/configure.xml     | 10 ++-
 libstdc++-v3/doc/xml/manual/evolution.xml     |  5 ++
 libstdc++-v3/doc/xml/manual/mt_allocator.xml  |  8 +--
 10 files changed, 64 insertions(+), 132 deletions(-)

diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 71321055de7..6d9a8875e31 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -2599,7 +2599,7 @@ AC_DEFUN([GLIBCXX_ENABLE_ALLOCATOR], [
   AC_MSG_CHECKING([for std::allocator base class])
   GLIBCXX_ENABLE(libstdcxx-allocator,auto,[[[=KIND]]],
     [use KIND for target std::allocator base],
-    [permit new|malloc|mt|bitmap|pool|yes|no|auto])
+    [permit new|malloc|yes|no|auto])
 
   # If they didn't use this option switch, or if they specified --enable
   # with no specific model, we'll have to look for one.  If they
@@ -2631,26 +2631,14 @@ AC_DEFUN([GLIBCXX_ENABLE_ALLOCATOR], [
 
   # Set configure bits for specified locale package
   case ${enable_libstdcxx_allocator_flag} in
-    bitmap)
-      ALLOCATOR_H=config/allocator/bitmap_allocator_base.h
-      ALLOCATOR_NAME=__gnu_cxx::bitmap_allocator
-      ;;
     malloc)
       ALLOCATOR_H=config/allocator/malloc_allocator_base.h
       ALLOCATOR_NAME=__gnu_cxx::malloc_allocator
       ;;
-    mt)
-      ALLOCATOR_H=config/allocator/mt_allocator_base.h
-      ALLOCATOR_NAME=__gnu_cxx::__mt_alloc
-      ;;
     new)
       ALLOCATOR_H=config/allocator/new_allocator_base.h
       ALLOCATOR_NAME=__gnu_cxx::new_allocator
       ;;
-    pool)
-      ALLOCATOR_H=config/allocator/pool_allocator_base.h
-      ALLOCATOR_NAME=__gnu_cxx::__pool_alloc
-      ;;
   esac
 
   GLIBCXX_CONDITIONAL(ENABLE_ALLOCATOR_NEW,
diff --git a/libstdc++-v3/doc/xml/manual/allocator.xml b/libstdc++-v3/doc/xml/manual/allocator.xml
index 1f429410eb0..aaab4e29aa7 100644
--- a/libstdc++-v3/doc/xml/manual/allocator.xml
+++ b/libstdc++-v3/doc/xml/manual/allocator.xml
@@ -154,8 +154,9 @@
    </para>
 
    <para>
-     The base class that <classname>allocator</classname> is derived from
-     may not be user-configurable.
+     The choice of base class that <classname>allocator</classname>
+     is derived from is fixed at the time when GCC is built,
+     and the different choices are not ABI compatible.
 </para>
 
   </section>
@@ -314,6 +315,13 @@
    <classname>new_allocator</classname>.
    </para>
 
+   <para>
+     Since C++11 the minimal interface require for an allocator is
+     much smaller, as <classname>std::allocator_traits</classname>
+     can provide default for much of the interface.
+   </para>
+
+
 </section>
 
 <section xml:id="allocator.ext"><info><title>Extension Allocators</title></info>
@@ -359,9 +367,10 @@
        <classname>debug_allocator</classname>
        </para>
        <para>
-	 A wrapper around an arbitrary allocator A.  It passes on
-	 slightly increased size requests to A, and uses the extra
-	 memory to store size information.  When a pointer is passed
+	 A wrapper around an arbitrary allocator <classname>A</classname>.
+	 It passes on slightly increased size requests to <classname>A</classname>,
+	 and uses the extra memory to store size information.
+	 When a pointer is passed
 	 to <function>deallocate()</function>, the stored size is
 	 checked, and <function>assert()</function> is used to
 	 guarantee they match.
@@ -393,52 +402,16 @@
        </para>
 
        <para>
-	 Older versions of this class take a boolean template
-	 parameter, called <varname>thr</varname>, and an integer template
-	 parameter, called <varname>inst</varname>.
+	 For thread-enabled configurations, the pool is locked with a
+	 single big lock. In some situations, this implementation detail
+	 may result in severe performance degradation.
        </para>
 
        <para>
-	 The <varname>inst</varname> number is used to track additional memory
-      pools.  The point of the number is to allow multiple
-      instantiations of the classes without changing the semantics at
-      all.  All three of
+	 (Note that the GCC thread abstraction layer allows us to provide
+	 safe zero-overhead stubs for the threading routines, if threads
+	 were disabled at configuration time.)
        </para>
-
-   <programlisting>
-    typedef  __pool_alloc&lt;true,0&gt;    normal;
-    typedef  __pool_alloc&lt;true,1&gt;    private;
-    typedef  __pool_alloc&lt;true,42&gt;   also_private;
-   </programlisting>
-   <para>
-     behave exactly the same way.  However, the memory pool for each type
-      (and remember that different instantiations result in different types)
-      remains separate.
-   </para>
-   <para>
-     The library uses <emphasis>0</emphasis> in all its instantiations.  If you
-      wish to keep separate free lists for a particular purpose, use a
-      different number.
-   </para>
-   <para>The <varname>thr</varname> boolean determines whether the
-   pool should be manipulated atomically or not.  When
-   <varname>thr</varname> = <constant>true</constant>, the allocator
-   is thread-safe, while <varname>thr</varname> =
-   <constant>false</constant>, is slightly faster but unsafe for
-   multiple threads.
-   </para>
-
-   <para>
-     For thread-enabled configurations, the pool is locked with a
-     single big lock. In some situations, this implementation detail
-     may result in severe performance degradation.
-   </para>
-
-   <para>
-     (Note that the GCC thread abstraction layer allows us to provide
-     safe zero-overhead stubs for the threading routines, if threads
-     were disabled at configuration time.)
-   </para>
      </listitem>
 
      <listitem>
diff --git a/libstdc++-v3/doc/xml/manual/configure.xml b/libstdc++-v3/doc/xml/manual/configure.xml
index cc9c8554c6c..8c26acc95a7 100644
--- a/libstdc++-v3/doc/xml/manual/configure.xml
+++ b/libstdc++-v3/doc/xml/manual/configure.xml
@@ -118,12 +118,10 @@
 
  <varlistentry><term><code>--enable-libstdcxx-allocator=OPTION  </code></term>
  <listitem><para>Select a target-specific underlying std::allocator.  The
-	choices are 'new' to specify a wrapper for new, 'malloc' to
-	specify a wrapper for malloc, 'mt' for a fixed power of two allocator,
-	'pool' for the SGI pooled allocator or 'bitmap' for a bitmap allocator.
-	See this page for more information on allocator
-	<link linkend="allocator.ext">extensions</link>. This option
-	can change the library ABI.
+	choices are 'new' to specify a wrapper for new, and 'malloc' to
+	specify a wrapper for malloc.
+	See <xref linkend="allocator.ext"/> for more information.
+	This option can change the library ABI.
      </para>
  </listitem></varlistentry>
 
diff --git a/libstdc++-v3/doc/xml/manual/evolution.xml b/libstdc++-v3/doc/xml/manual/evolution.xml
index 9aef84a0933..271d2225c3a 100644
--- a/libstdc++-v3/doc/xml/manual/evolution.xml
+++ b/libstdc++-v3/doc/xml/manual/evolution.xml
@@ -1033,6 +1033,11 @@ accessors for the unexpected handler are deprecated for C++11 and later.
 Dynamic exception specifications should be replaced with <code>noexcept</code>.
 </para>
 
+<para>
+The <literal>bitmap</literal>, <literal>mt</literal>, and <literal>pool</literal>
+options for <option>--enable-libstdcxx-allocator</option> were removed.
+</para>
+
 </section>
 
 </section>
diff --git a/libstdc++-v3/doc/xml/manual/mt_allocator.xml b/libstdc++-v3/doc/xml/manual/mt_allocator.xml
index 93504a7d711..f1c09b3bd8f 100644
--- a/libstdc++-v3/doc/xml/manual/mt_allocator.xml
+++ b/libstdc++-v3/doc/xml/manual/mt_allocator.xml
@@ -20,12 +20,12 @@
 <para>
   The mt allocator [hereinafter referred to simply as "the allocator"]
   is a fixed size (power of two) allocator that was initially
-  developed specifically to suit the needs of multi threaded
+  developed specifically to suit the needs of multi-threaded
   applications [hereinafter referred to as an MT application]. Over
   time the allocator has evolved and been improved in many ways, in
-  particular it now also does a good job in single threaded
-  applications [hereinafter referred to as a ST application]. (Note:
-  In this document, when referring to single threaded applications
+  particular it now also does a good job in single-threaded
+  applications [hereinafter referred to as an ST application]. (Note:
+  In this document, when referring to single-threaded applications
   this also includes applications that are compiled with gcc without
   thread support enabled. This is accomplished using ifdef's on
   __GTHREADS). This allocator is tunable, very flexible, and capable
-- 
2.31.1

Re: [PATCH] libstdc++: Remove broken std::allocator base classes [PR103340]

[Jonathan Wakely]

[-- Attachment #1: Type: text/plain, Size: 661 bytes --]

On Wed, 24 Nov 2021 at 13:25, Jonathan Wakely via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> I plan to commit this Real Soon. Please yell if you need these
> alternative std::allocator back-ends to stay (and explain how you're
> using them when they've  been broken for years, and start sending test
> results to the gcc-testresults mailing list, and ideally offer to
> maintain them).
>
> Tested powerpc64le-linux.

Nobody has objected or said they need these so I'm going ahead with
removing them.

This version of the patch also removes the
config/allocator/*_allocator_base.h headers that are no longer needed.

Tested powerpc64le-linux, pushed to trunk.

[-- Attachment #2: patch.txt --]
[-- Type: text/plain, Size: 16575 bytes --]

commit e2e98f524fdb80c16e3395f20fee930fbcad5562
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Dec 1 16:30:30 2021

    libstdc++: Remove broken std::allocator base classes [PR103340]
    
    The bitmap_allocator, __mt_alloc and __pool_alloc extensions are no
    longer suitable for use as the base class of std::allocator, because
    they have not been updated to meet the C++20 requirements.  There is a
    patch attached to PR 103340 which addresses that, but more work would be
    needed to solve the linking errors that occur when the library is
    configured to use them.
    
    Using --enable-libstdcxx-allocator=bitmap wouldn't even bootstrap for
    the past few years, and I can't find any gcc-testresults reports using
    any of these allocators. This patch removes the configure option to use
    these as the std::allocator base class. The allocators are still in the
    tree and can be used directly, you just can't configure the library to
    use one of them as the base class of std::allocator.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/103340
            PR libstdc++/103400
            PR libstdc++/103381
            * acinclude.m4 (GLIBCXX_ENABLE_ALLOCATOR): Remove mt, bitmap
            and pool options.
            * configure: Regenerate.
            * config/allocator/bitmap_allocator_base.h: Removed.
            * config/allocator/mt_allocator_base.h: Removed.
            * config/allocator/pool_allocator_base.h: Removed.
            * doc/xml/manual/allocator.xml: Update.
            * doc/xml/manual/configure.xml: Update.
            * doc/xml/manual/evolution.xml: Document removal.
            * doc/xml/manual/mt_allocator.xml: Editorial tweaks.
            * doc/html/manual/*: Regenerate.

diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 71321055de7..6d9a8875e31 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -2599,7 +2599,7 @@ AC_DEFUN([GLIBCXX_ENABLE_ALLOCATOR], [
   AC_MSG_CHECKING([for std::allocator base class])
   GLIBCXX_ENABLE(libstdcxx-allocator,auto,[[[=KIND]]],
     [use KIND for target std::allocator base],
-    [permit new|malloc|mt|bitmap|pool|yes|no|auto])
+    [permit new|malloc|yes|no|auto])
 
   # If they didn't use this option switch, or if they specified --enable
   # with no specific model, we'll have to look for one.  If they
@@ -2631,26 +2631,14 @@ AC_DEFUN([GLIBCXX_ENABLE_ALLOCATOR], [
 
   # Set configure bits for specified locale package
   case ${enable_libstdcxx_allocator_flag} in
-    bitmap)
-      ALLOCATOR_H=config/allocator/bitmap_allocator_base.h
-      ALLOCATOR_NAME=__gnu_cxx::bitmap_allocator
-      ;;
     malloc)
       ALLOCATOR_H=config/allocator/malloc_allocator_base.h
       ALLOCATOR_NAME=__gnu_cxx::malloc_allocator
       ;;
-    mt)
-      ALLOCATOR_H=config/allocator/mt_allocator_base.h
-      ALLOCATOR_NAME=__gnu_cxx::__mt_alloc
-      ;;
     new)
       ALLOCATOR_H=config/allocator/new_allocator_base.h
       ALLOCATOR_NAME=__gnu_cxx::new_allocator
       ;;
-    pool)
-      ALLOCATOR_H=config/allocator/pool_allocator_base.h
-      ALLOCATOR_NAME=__gnu_cxx::__pool_alloc
-      ;;
   esac
 
   GLIBCXX_CONDITIONAL(ENABLE_ALLOCATOR_NEW,
diff --git a/libstdc++-v3/config/allocator/bitmap_allocator_base.h b/libstdc++-v3/config/allocator/bitmap_allocator_base.h
deleted file mode 100644
index 40ccbf03449..00000000000
--- a/libstdc++-v3/config/allocator/bitmap_allocator_base.h
+++ /dev/null
@@ -1,55 +0,0 @@
-// Base to std::allocator -*- C++ -*-
-
-// Copyright (C) 2004-2021 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/c++allocator.h
- *  This is an internal header file, included by other library headers.
- *  Do not attempt to use it directly. @headername{memory}
- */
-
-#ifndef _GLIBCXX_CXX_ALLOCATOR_H
-#define _GLIBCXX_CXX_ALLOCATOR_H 1
-
-#include <ext/bitmap_allocator.h>
-
-#if __cplusplus >= 201103L
-namespace std
-{
-  /**
-   *  @brief  An alias to the base class for std::allocator.
-   *  @ingroup allocators
-   *
-   *  Used to set the std::allocator base class to
-   *  __gnu_cxx::bitmap_allocator.
-   *
-   *  @tparam  _Tp  Type of allocated object.
-    */
-  template<typename _Tp>
-    using __allocator_base = __gnu_cxx::bitmap_allocator<_Tp>;
-}
-#else
-// Define bitmap_allocator as the base class to std::allocator.
-# define __allocator_base  __gnu_cxx::bitmap_allocator
-#endif
-
-#endif
diff --git a/libstdc++-v3/config/allocator/mt_allocator_base.h b/libstdc++-v3/config/allocator/mt_allocator_base.h
deleted file mode 100644
index eb45b8dea6d..00000000000
--- a/libstdc++-v3/config/allocator/mt_allocator_base.h
+++ /dev/null
@@ -1,55 +0,0 @@
-// Base to std::allocator -*- C++ -*-
-
-// Copyright (C) 2004-2021 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/c++allocator.h
- *  This is an internal header file, included by other library headers.
- *  Do not attempt to use it directly. @headername{memory}
- */
-
-#ifndef _GLIBCXX_CXX_ALLOCATOR_H
-#define _GLIBCXX_CXX_ALLOCATOR_H 1
-
-#include <ext/mt_allocator.h>
-
-#if __cplusplus >= 201103L
-namespace std
-{
-  /**
-   *  @brief  An alias to the base class for std::allocator.
-   *  @ingroup allocators
-   *
-   *  Used to set the std::allocator base class to
-   *  __gnu_cxx::__mt_alloc.
-   *
-   *  @tparam  _Tp  Type of allocated object.
-    */
-  template<typename _Tp>
-    using __allocator_base = __gnu_cxx::__mt_alloc<_Tp>;
-}
-#else
-// Define __mt_alloc as the base class to std::allocator.
-# define __allocator_base  __gnu_cxx::__mt_alloc
-#endif
-
-#endif
diff --git a/libstdc++-v3/config/allocator/pool_allocator_base.h b/libstdc++-v3/config/allocator/pool_allocator_base.h
deleted file mode 100644
index c3ec8ecce8d..00000000000
--- a/libstdc++-v3/config/allocator/pool_allocator_base.h
+++ /dev/null
@@ -1,55 +0,0 @@
-// Base to std::allocator -*- C++ -*-
-
-// Copyright (C) 2004-2021 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/c++allocator.h
- *  This is an internal header file, included by other library headers.
- *  Do not attempt to use it directly. @headername{memory}
- */
-
-#ifndef _GLIBCXX_CXX_ALLOCATOR_H
-#define _GLIBCXX_CXX_ALLOCATOR_H 1
-
-#include <ext/pool_allocator.h>
-
-#if __cplusplus >= 201103L
-namespace std
-{
-  /**
-   *  @brief  An alias to the base class for std::allocator.
-   *  @ingroup allocators
-   *
-   *  Used to set the std::allocator base class to
-   *  __gnu_cxx::__pool_alloc.
-   *
-   *  @tparam  _Tp  Type of allocated object.
-    */
-  template<typename _Tp>
-    using __allocator_base = __gnu_cxx::__pool_alloc<_Tp>;
-}
-#else
-// Define __pool_alloc as the base class to std::allocator.
-# define __allocator_base  __gnu_cxx::__pool_alloc
-#endif
-
-#endif
diff --git a/libstdc++-v3/doc/xml/manual/allocator.xml b/libstdc++-v3/doc/xml/manual/allocator.xml
index 1f429410eb0..aaab4e29aa7 100644
--- a/libstdc++-v3/doc/xml/manual/allocator.xml
+++ b/libstdc++-v3/doc/xml/manual/allocator.xml
@@ -154,8 +154,9 @@
    </para>
 
    <para>
-     The base class that <classname>allocator</classname> is derived from
-     may not be user-configurable.
+     The choice of base class that <classname>allocator</classname>
+     is derived from is fixed at the time when GCC is built,
+     and the different choices are not ABI compatible.
 </para>
 
   </section>
@@ -314,6 +315,13 @@
    <classname>new_allocator</classname>.
    </para>
 
+   <para>
+     Since C++11 the minimal interface require for an allocator is
+     much smaller, as <classname>std::allocator_traits</classname>
+     can provide default for much of the interface.
+   </para>
+
+
 </section>
 
 <section xml:id="allocator.ext"><info><title>Extension Allocators</title></info>
@@ -359,9 +367,10 @@
        <classname>debug_allocator</classname>
        </para>
        <para>
-	 A wrapper around an arbitrary allocator A.  It passes on
-	 slightly increased size requests to A, and uses the extra
-	 memory to store size information.  When a pointer is passed
+	 A wrapper around an arbitrary allocator <classname>A</classname>.
+	 It passes on slightly increased size requests to <classname>A</classname>,
+	 and uses the extra memory to store size information.
+	 When a pointer is passed
 	 to <function>deallocate()</function>, the stored size is
 	 checked, and <function>assert()</function> is used to
 	 guarantee they match.
@@ -393,52 +402,16 @@
        </para>
 
        <para>
-	 Older versions of this class take a boolean template
-	 parameter, called <varname>thr</varname>, and an integer template
-	 parameter, called <varname>inst</varname>.
+	 For thread-enabled configurations, the pool is locked with a
+	 single big lock. In some situations, this implementation detail
+	 may result in severe performance degradation.
        </para>
 
        <para>
-	 The <varname>inst</varname> number is used to track additional memory
-      pools.  The point of the number is to allow multiple
-      instantiations of the classes without changing the semantics at
-      all.  All three of
+	 (Note that the GCC thread abstraction layer allows us to provide
+	 safe zero-overhead stubs for the threading routines, if threads
+	 were disabled at configuration time.)
        </para>
-
-   <programlisting>
-    typedef  __pool_alloc&lt;true,0&gt;    normal;
-    typedef  __pool_alloc&lt;true,1&gt;    private;
-    typedef  __pool_alloc&lt;true,42&gt;   also_private;
-   </programlisting>
-   <para>
-     behave exactly the same way.  However, the memory pool for each type
-      (and remember that different instantiations result in different types)
-      remains separate.
-   </para>
-   <para>
-     The library uses <emphasis>0</emphasis> in all its instantiations.  If you
-      wish to keep separate free lists for a particular purpose, use a
-      different number.
-   </para>
-   <para>The <varname>thr</varname> boolean determines whether the
-   pool should be manipulated atomically or not.  When
-   <varname>thr</varname> = <constant>true</constant>, the allocator
-   is thread-safe, while <varname>thr</varname> =
-   <constant>false</constant>, is slightly faster but unsafe for
-   multiple threads.
-   </para>
-
-   <para>
-     For thread-enabled configurations, the pool is locked with a
-     single big lock. In some situations, this implementation detail
-     may result in severe performance degradation.
-   </para>
-
-   <para>
-     (Note that the GCC thread abstraction layer allows us to provide
-     safe zero-overhead stubs for the threading routines, if threads
-     were disabled at configuration time.)
-   </para>
      </listitem>
 
      <listitem>
diff --git a/libstdc++-v3/doc/xml/manual/configure.xml b/libstdc++-v3/doc/xml/manual/configure.xml
index cc9c8554c6c..8c26acc95a7 100644
--- a/libstdc++-v3/doc/xml/manual/configure.xml
+++ b/libstdc++-v3/doc/xml/manual/configure.xml
@@ -118,12 +118,10 @@
 
  <varlistentry><term><code>--enable-libstdcxx-allocator=OPTION  </code></term>
  <listitem><para>Select a target-specific underlying std::allocator.  The
-	choices are 'new' to specify a wrapper for new, 'malloc' to
-	specify a wrapper for malloc, 'mt' for a fixed power of two allocator,
-	'pool' for the SGI pooled allocator or 'bitmap' for a bitmap allocator.
-	See this page for more information on allocator
-	<link linkend="allocator.ext">extensions</link>. This option
-	can change the library ABI.
+	choices are 'new' to specify a wrapper for new, and 'malloc' to
+	specify a wrapper for malloc.
+	See <xref linkend="allocator.ext"/> for more information.
+	This option can change the library ABI.
      </para>
  </listitem></varlistentry>
 
diff --git a/libstdc++-v3/doc/xml/manual/evolution.xml b/libstdc++-v3/doc/xml/manual/evolution.xml
index 9aef84a0933..271d2225c3a 100644
--- a/libstdc++-v3/doc/xml/manual/evolution.xml
+++ b/libstdc++-v3/doc/xml/manual/evolution.xml
@@ -1033,6 +1033,11 @@ accessors for the unexpected handler are deprecated for C++11 and later.
 Dynamic exception specifications should be replaced with <code>noexcept</code>.
 </para>
 
+<para>
+The <literal>bitmap</literal>, <literal>mt</literal>, and <literal>pool</literal>
+options for <option>--enable-libstdcxx-allocator</option> were removed.
+</para>
+
 </section>
 
 </section>
diff --git a/libstdc++-v3/doc/xml/manual/mt_allocator.xml b/libstdc++-v3/doc/xml/manual/mt_allocator.xml
index 93504a7d711..f1c09b3bd8f 100644
--- a/libstdc++-v3/doc/xml/manual/mt_allocator.xml
+++ b/libstdc++-v3/doc/xml/manual/mt_allocator.xml
@@ -20,12 +20,12 @@
 <para>
   The mt allocator [hereinafter referred to simply as "the allocator"]
   is a fixed size (power of two) allocator that was initially
-  developed specifically to suit the needs of multi threaded
+  developed specifically to suit the needs of multi-threaded
   applications [hereinafter referred to as an MT application]. Over
   time the allocator has evolved and been improved in many ways, in
-  particular it now also does a good job in single threaded
-  applications [hereinafter referred to as a ST application]. (Note:
-  In this document, when referring to single threaded applications
+  particular it now also does a good job in single-threaded
+  applications [hereinafter referred to as an ST application]. (Note:
+  In this document, when referring to single-threaded applications
   this also includes applications that are compiled with gcc without
   thread support enabled. This is accomplished using ifdef's on
   __GTHREADS). This allocator is tunable, very flexible, and capable

[wwwdocs] Document --enable-libstdcxx-allocator changes

[Jonathan Wakely]

Pushed to wwwdocs.


---
 htdocs/gcc-12/changes.html | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/htdocs/gcc-12/changes.html b/htdocs/gcc-12/changes.html
index 000501fb..c2b87a53 100644
--- a/htdocs/gcc-12/changes.html
+++ b/htdocs/gcc-12/changes.html
@@ -41,6 +41,11 @@ a work-in-progress.</p>
     member instead of a literal <code>0</code>, as this is portable to other
     C++ implementations.
   </li>
+  <li>The configuration option <code>--enable-libstdcxx-allocator</code>
+    no longer supports the <code>bitmap</code>, <code>mt</code>, and
+    <code>pool</code> arguments. Those configurations had been broken for
+    some time.
+  </li>
   <li>
     <strong>Fortran:</strong>
     OpenMP code using the <code>omp_lib.h</code> include file can no longer be
-- 
2.31.1