Patchwork fix libstdc++/56012 - narrowing conversion in std::atomic_flag

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Submitter Jonathan Wakely
Date Feb. 26, 2013, 11:46 p.m.
Message ID <CAH6eHdR4UHGV+6x=XbccD8OFkX1jdxsK2rR25bs86J-Vdw11nQ@mail.gmail.com>
Download mbox | patch
Permalink /patch/223430/
State New
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Comments

Jonathan Wakely - Feb. 26, 2013, 11:46 p.m.
On 17 January 2013 00:21, Jonathan Wakely wrote:
> This fixes a regression since 4.6 when -Wsystem-headers is used.  The
> initialization of the __atomic_flag_base base class has a narrowing
> conversion from int (the macro) to either bool or unsigned char.  The
> patch fixes it by calling a constexpr function which implicitly
> converts the value to the return type instead of doing the conversion
> inside a braced-init-list.  Doing that requires naming the return
> type, so I defined a new typedef for to avoid duplicating the
> preprocessor conditional.  The patch also adds a missing assignment
> operator in atomic<bool>.
>
>         PR libstdc++/56012
>         * include/bits/atomic_base.h (atomic_flag): Fix narrowing conversion.
>         * testsuite/29_atomics/atomic/operators/56012.cc: New.
>
>         PR libstdc++/56011
>         * include/std/atomic (atomic<bool>::operator=(bool) volatile): Add
>         missing overload.
>         * testsuite/29_atomics/atomic/operators/56011.cc: New.
>
> Tested x86_64-linux, it's a regression so I want to commit it to the
> trunk and 4.7 branch, any objections from the atomics experts?

Committed to trunk, 4.7 to follow soon.
commit 9f33378b56382e14dce6279d40d44c268de714f8
Author: Jonathan Wakely <jwakely.gcc@gmail.com>
Date:   Tue Feb 26 23:40:56 2013 +0000

    	PR libstdc++/56012
    	* include/bits/atomic_base.h (atomic_flag): Fix narrowing conversion.
    	* testsuite/29_atomics/atomic/operators/56012.cc: New.
    
    	PR libstdc++/56011
    	* include/std/atomic (atomic<bool>::operator=(bool) volatile): Add
    	missing overload.
    	* testsuite/29_atomics/atomic/operators/56011.cc: New.

Patch

diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h
index b44e990..609fe8b 100644
--- a/libstdc++-v3/include/bits/atomic_base.h
+++ b/libstdc++-v3/include/bits/atomic_base.h
@@ -239,6 +239,12 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp>
     struct atomic<_Tp*>;
 
+    /* The target's "set" value for test-and-set may not be exactly 1.  */
+#if __GCC_ATOMIC_TEST_AND_SET_TRUEVAL == 1
+    typedef bool __atomic_flag_data_type;
+#else
+    typedef unsigned char __atomic_flag_data_type;
+#endif
 
   /**
    *  @brief Base type for atomic_flag.
@@ -254,12 +260,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   struct __atomic_flag_base
   {
-    /* The target's "set" value for test-and-set may not be exactly 1.  */
-#if __GCC_ATOMIC_TEST_AND_SET_TRUEVAL == 1
-    bool _M_i;
-#else
-    unsigned char _M_i;
-#endif
+    __atomic_flag_data_type _M_i;
   };
 
   _GLIBCXX_END_EXTERN_C
@@ -277,7 +278,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     // Conversion to ATOMIC_FLAG_INIT.
     constexpr atomic_flag(bool __i) noexcept
-      : __atomic_flag_base({ __i ? __GCC_ATOMIC_TEST_AND_SET_TRUEVAL : 0 })
+      : __atomic_flag_base{ _S_init(__i) }
     { }
 
     bool
@@ -313,6 +314,11 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       __atomic_clear (&_M_i, __m);
     }
+
+  private:
+    static constexpr __atomic_flag_data_type
+    _S_init(bool __i)
+    { return __i ? __GCC_ATOMIC_TEST_AND_SET_TRUEVAL : 0; }
   };
 
 
diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic
index 8ed53eb..813f574 100644
--- a/libstdc++-v3/include/std/atomic
+++ b/libstdc++-v3/include/std/atomic
@@ -69,6 +69,10 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     operator=(bool __i) noexcept
     { return _M_base.operator=(__i); }
 
+    bool
+    operator=(bool __i) volatile noexcept
+    { return _M_base.operator=(__i); }
+
     operator bool() const noexcept
     { return _M_base.load(); }
 
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/operators/56011.cc b/libstdc++-v3/testsuite/29_atomics/atomic/operators/56011.cc
new file mode 100644
index 0000000..1d77a55
--- /dev/null
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/operators/56011.cc
@@ -0,0 +1,29 @@ 
+// { dg-options "-std=gnu++0x" }
+// { dg-do compile }
+
+// Copyright (C) 2013 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.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <atomic>
+void test01()
+{
+  using namespace std;
+  volatile atomic<bool> ab1 __attribute__((unused));
+  ab1 = true;
+  volatile atomic_bool ab2 __attribute__((unused));
+  ab2 = true;
+}
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_flag/cons/56012.cc b/libstdc++-v3/testsuite/29_atomics/atomic_flag/cons/56012.cc
new file mode 100644
index 0000000..64f3b972
--- /dev/null
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_flag/cons/56012.cc
@@ -0,0 +1,26 @@ 
+// { dg-options "-std=gnu++0x -Wsystem-headers -Wnarrowing" }
+// { dg-do compile }
+
+// Copyright (C) 2013 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.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <atomic>
+void test01()
+{
+  using namespace std;
+  atomic_flag af __attribute__((unused)) = ATOMIC_FLAG_INIT;
+}