From: Richard Henderson <rth@redhat.com>
Date: Thu, 26 Mar 2015 18:31:11 +0000 (-0700)
Subject: re PR libstdc++/65033 (C++11 atomics: is_lock_free result does not always match the... 
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=8be568519bf08098e056567d57a75c3f38416ac2;p=gcc.git

re PR libstdc++/65033 (C++11 atomics: is_lock_free result does not always match the real lock-free property)

PR libstdc++/65033

 * include/bits/atomic_base.h (__atomic_base<T>::is_lock_free): Build
 a fake pointer indicating type alignment.
 (__atomic_base<T *>::is_lock_free): Likewise.
 * include/std/atomic (atomic<T>::is_lock_free): Likewise.

From-SVN: r221701
---

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 6793e9d39d6..cd4640a39e3 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,11 @@
+2015-03-26  Richard Henderson  <rth@redhat.com>
+
+	PR libstdc++/65033
+	* include/bits/atomic_base.h (__atomic_base<T>::is_lock_free): Build
+	a fake pointer indicating type alignment.
+	(__atomic_base<T *>::is_lock_free): Likewise.
+	* include/std/atomic (atomic<T>::is_lock_free): Likewise.
+
 2015-03-25  Alan Lawrence  <alan.lawrence@arm.com>
 
 	PR libstdc++/33394
diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h
index fe6524f41b7..8104c986b52 100644
--- a/libstdc++-v3/include/bits/atomic_base.h
+++ b/libstdc++-v3/include/bits/atomic_base.h
@@ -346,11 +346,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       bool
       is_lock_free() const noexcept
-      { return __atomic_is_lock_free(sizeof(_M_i), nullptr); }
+      {
+	// Produce a fake, minimally aligned pointer.
+	void *__a = reinterpret_cast<void *>(-__alignof(_M_i));
+	return __atomic_is_lock_free(sizeof(_M_i), __a);
+      }
 
       bool
       is_lock_free() const volatile noexcept
-      { return __atomic_is_lock_free(sizeof(_M_i), nullptr); }
+      {
+	// Produce a fake, minimally aligned pointer.
+	void *__a = reinterpret_cast<void *>(-__alignof(_M_i));
+	return __atomic_is_lock_free(sizeof(_M_i), __a);
+      }
 
       _GLIBCXX_ALWAYS_INLINE void
       store(__int_type __i, memory_order __m = memory_order_seq_cst) noexcept
@@ -653,11 +661,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       bool
       is_lock_free() const noexcept
-      { return __atomic_is_lock_free(sizeof(__pointer_type), nullptr); }
+      {
+	// Produce a fake, minimally aligned pointer.
+	void *__a = reinterpret_cast<void *>(-__alignof(_M_p));
+	return __atomic_is_lock_free(sizeof(_M_p), __a);
+      }
 
       bool
       is_lock_free() const volatile noexcept
-      { return __atomic_is_lock_free(sizeof(__pointer_type), nullptr); }
+      {
+	// Produce a fake, minimally aligned pointer.
+	void *__a = reinterpret_cast<void *>(-__alignof(_M_p));
+	return __atomic_is_lock_free(sizeof(_M_p), __a);
+      }
 
       _GLIBCXX_ALWAYS_INLINE void
       store(__pointer_type __p,
diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic
index 1a17427e231..cc4b5f1a94c 100644
--- a/libstdc++-v3/include/std/atomic
+++ b/libstdc++-v3/include/std/atomic
@@ -198,11 +198,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       bool
       is_lock_free() const noexcept
-      { return __atomic_is_lock_free(sizeof(_M_i), nullptr); }
+      {
+	// Produce a fake, minimally aligned pointer.
+	void *__a = reinterpret_cast<void *>(-__alignof(_M_i));
+	return __atomic_is_lock_free(sizeof(_M_i), __a);
+      }
 
       bool
       is_lock_free() const volatile noexcept
-      { return __atomic_is_lock_free(sizeof(_M_i), nullptr); }
+      {
+	// Produce a fake, minimally aligned pointer.
+	void *__a = reinterpret_cast<void *>(-__alignof(_M_i));
+	return __atomic_is_lock_free(sizeof(_M_i), __a);
+      }
 
       void
       store(_Tp __i, memory_order __m = memory_order_seq_cst) noexcept