Use atomics in guard.cc.

This provides proper definitions for _GLIBCXX_READ_MEM_BARRIER and
_GLIBCXX_WRITE_MEM_BARRIER, rewrites the guards in terms of proper
atomic extensions and removes internal uses of
_GLIBCXX_READ_MEM_BARRIER and _GLIBCXX_WRITE_MEM_BARRIER and replaces
them with equivalent atomics.

2015-06-12  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>

	PR target/66200
	PR c++/66192
	* * config/cpu/generic/atomic_word.h (_GLIBCXX_READ_MEM_BARRIER): Define
        (_GLIBCXX_WRITE_MEM_BARRIER): Likewise
        * include/bits/shared_ptr_base.h: Use ACQ_REL barrier.
        * include/ext/atomicity.h: Likewise.
        * include/tr1/shared_ptr.h: Likewise.
        * libsupc++/guard.cc (__test_and_acquire): Rewrite with atomics.
        Update comment.
        (__set_and_release): Likewise.
        * testsuite/20_util/shared_ptr/cons/43820_neg.cc (test01): Adjust for
	line numbers.
        * testsuite/20_util/shared_ptr/cons/void_neg.cc: Likewise.
        * testsuite/tr1/2_general_utilities/shared_ptr/cons/43820_neg.cc:
	Likewise.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@224411 138bc75d-0d04-0410-961f-82ee72b054a4

9 files changed, 47 insertions, 31 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 91a5d885228..444d24e068e 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,21 @@
+2015-06-12  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>
+
+	PR target/66200
+	PR c++/66192
+	* * config/cpu/generic/atomic_word.h (_GLIBCXX_READ_MEM_BARRIER): Define
+        (_GLIBCXX_WRITE_MEM_BARRIER): Likewise
+        * include/bits/shared_ptr_base.h: Use ACQ_REL barrier.
+        * include/ext/atomicity.h: Likewise.
+        * include/tr1/shared_ptr.h: Likewise.
+        * libsupc++/guard.cc (__test_and_acquire): Rewrite with atomics.
+        Update comment.
+        (__set_and_release): Likewise.
+        * testsuite/20_util/shared_ptr/cons/43820_neg.cc (test01): Adjust for
+	line numbers.
+        * testsuite/20_util/shared_ptr/cons/void_neg.cc: Likewise.
+        * testsuite/tr1/2_general_utilities/shared_ptr/cons/43820_neg.cc:
+	Likewise.
+
 2015-06-12  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/std/tuple (__is_tuple_like_impl): Disambiguate array in
diff --git a/libstdc++-v3/config/cpu/generic/atomic_word.h b/libstdc++-v3/config/cpu/generic/atomic_word.h
index 19038bb6e06..ccf1e5a5ab1 100644
--- a/libstdc++-v3/config/cpu/generic/atomic_word.h
+++ b/libstdc++-v3/config/cpu/generic/atomic_word.h
@@ -31,17 +31,10 @@
 
 typedef int _Atomic_word;
 
-// Define these two macros using the appropriate memory barrier for the target.
-// The commented out versions below are the defaults.
-// See ia64/atomic_word.h for an alternative approach.
-
-// This one prevents loads from being hoisted across the barrier;
-// in other words, this is a Load-Load acquire barrier.
-// This is necessary iff TARGET_RELAXED_ORDERING is defined in tm.h.  
-// #define _GLIBCXX_READ_MEM_BARRIER __asm __volatile ("":::"memory")
-
-// This one prevents stores from being sunk across the barrier; in other
-// words, a Store-Store release barrier.
-// #define _GLIBCXX_WRITE_MEM_BARRIER __asm __volatile ("":::"memory")
+
+// This is a memory order acquire fence.
+#define _GLIBCXX_READ_MEM_BARRIER __atomic_thread_fence (__ATOMIC_ACQUIRE)
+// This is a memory order release fence.
+#define _GLIBCXX_WRITE_MEM_BARRIER __atomic_thread_fence (__ATOMIC_RELEASE)
 
 #endif 
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h b/libstdc++-v3/include/bits/shared_ptr_base.h
index 081df8781a3..aec10fecdbf 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -154,8 +154,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    // See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
 	    if (_Mutex_base<_Lp>::_S_need_barriers)
 	      {
-	        _GLIBCXX_READ_MEM_BARRIER;
-	        _GLIBCXX_WRITE_MEM_BARRIER;
+		__atomic_thread_fence (__ATOMIC_ACQ_REL);
 	      }
 
             // Be race-detector-friendly.  For more info see bits/c++config.
@@ -185,8 +184,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	      {
 	        // See _M_release(),
 	        // destroy() must observe results of dispose()
-	        _GLIBCXX_READ_MEM_BARRIER;
-	        _GLIBCXX_WRITE_MEM_BARRIER;
+		__atomic_thread_fence (__ATOMIC_ACQ_REL);
 	      }
 	    _M_destroy();
 	  }
diff --git a/libstdc++-v3/include/ext/atomicity.h b/libstdc++-v3/include/ext/atomicity.h
index aff33f84354..6d32cc48b4a 100644
--- a/libstdc++-v3/include/ext/atomicity.h
+++ b/libstdc++-v3/include/ext/atomicity.h
@@ -108,10 +108,10 @@ _GLIBCXX_END_NAMESPACE_VERSION
 // that the compiler doesn't reorder memory accesses across the
 // barriers.
 #ifndef _GLIBCXX_READ_MEM_BARRIER
-#define _GLIBCXX_READ_MEM_BARRIER __asm __volatile ("":::"memory")
+#define _GLIBCXX_READ_MEM_BARRIER __atomic_thread_fence (__ATOMIC_ACQUIRE)
 #endif
 #ifndef _GLIBCXX_WRITE_MEM_BARRIER
-#define _GLIBCXX_WRITE_MEM_BARRIER __asm __volatile ("":::"memory")
+#define _GLIBCXX_WRITE_MEM_BARRIER __atomic_thread_fence (__ATOMIC_RELEASE)
 #endif
 
 #endif 
diff --git a/libstdc++-v3/include/tr1/shared_ptr.h b/libstdc++-v3/include/tr1/shared_ptr.h
index ebb9d3621d7..a1c7d720307 100644
--- a/libstdc++-v3/include/tr1/shared_ptr.h
+++ b/libstdc++-v3/include/tr1/shared_ptr.h
@@ -145,8 +145,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    // See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
 	    if (_Mutex_base<_Lp>::_S_need_barriers)
 	      {
-	        _GLIBCXX_READ_MEM_BARRIER;
-	        _GLIBCXX_WRITE_MEM_BARRIER;
+		__atomic_thread_fence (__ATOMIC_ACQ_REL);
 	      }
 
             // Be race-detector-friendly.  For more info see bits/c++config.
@@ -176,8 +175,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	      {
 	        // See _M_release(),
 	        // destroy() must observe results of dispose()
-	        _GLIBCXX_READ_MEM_BARRIER;
-	        _GLIBCXX_WRITE_MEM_BARRIER;
+		__atomic_thread_fence (__ATOMIC_ACQ_REL);
 	      }
 	    _M_destroy();
 	  }
diff --git a/libstdc++-v3/libsupc++/guard.cc b/libstdc++-v3/libsupc++/guard.cc
index 9f19fd462ef..4a2cfe938a9 100644
--- a/libstdc++-v3/libsupc++/guard.cc
+++ b/libstdc++-v3/libsupc++/guard.cc
@@ -107,22 +107,31 @@ namespace
 # endif
 
 # ifndef _GLIBCXX_GUARD_TEST_AND_ACQUIRE
+
+// Test the guard variable with a memory load with
+// acquire semantics.
+
 inline bool
 __test_and_acquire (__cxxabiv1::__guard *g)
 {
-  bool b = _GLIBCXX_GUARD_TEST (g);
-  _GLIBCXX_READ_MEM_BARRIER;
-  return b;
+  unsigned char __c;
+  unsigned char *__p = reinterpret_cast<unsigned char *>(g);
+  __atomic_load (__p, &__c,  __ATOMIC_ACQUIRE);
+  return _GLIBCXX_GUARD_TEST(&__c);
 }
 #  define _GLIBCXX_GUARD_TEST_AND_ACQUIRE(G) __test_and_acquire (G)
 # endif
 
 # ifndef _GLIBCXX_GUARD_SET_AND_RELEASE
+
+// Set the guard variable to 1 with memory order release semantics.
+
 inline void
 __set_and_release (__cxxabiv1::__guard *g)
 {
-  _GLIBCXX_WRITE_MEM_BARRIER;
-  _GLIBCXX_GUARD_SET (g);
+  unsigned char *__p = reinterpret_cast<unsigned char *>(g);
+  unsigned char val = 1;
+  __atomic_store (__p, &val, __ATOMIC_RELEASE);
 }
 #  define _GLIBCXX_GUARD_SET_AND_RELEASE(G) __set_and_release (G)
 # endif
diff --git a/libstdc++-v3/testsuite/20_util/shared_ptr/cons/43820_neg.cc b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/43820_neg.cc
index 62555225432..fdfb7d93a72 100644
--- a/libstdc++-v3/testsuite/20_util/shared_ptr/cons/43820_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/43820_neg.cc
@@ -32,7 +32,7 @@ void test01()
 {
   X* px = 0;
   std::shared_ptr<X> p1(px);   // { dg-error "here" }
-  // { dg-error "incomplete" "" { target *-*-* } 891 }
+  // { dg-error "incomplete" "" { target *-*-* } 889 }
 
   std::shared_ptr<X> p9(ap());  // { dg-error "here" }
   // { dg-error "incomplete" "" { target *-*-* } 307 }
diff --git a/libstdc++-v3/testsuite/20_util/shared_ptr/cons/void_neg.cc b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/void_neg.cc
index 3f6c4ae97fc..10074c149fa 100644
--- a/libstdc++-v3/testsuite/20_util/shared_ptr/cons/void_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/shared_ptr/cons/void_neg.cc
@@ -25,5 +25,5 @@
 void test01()
 {
   std::shared_ptr<void> p((void*)nullptr);   // { dg-error "here" }
-  // { dg-error "incomplete" "" { target *-*-* } 890 }
+  // { dg-error "incomplete" "" { target *-*-* } 888 }
 }
diff --git a/libstdc++-v3/testsuite/tr1/2_general_utilities/shared_ptr/cons/43820_neg.cc b/libstdc++-v3/testsuite/tr1/2_general_utilities/shared_ptr/cons/43820_neg.cc
index 276c6a53337..3f44eb7292d 100644
--- a/libstdc++-v3/testsuite/tr1/2_general_utilities/shared_ptr/cons/43820_neg.cc
+++ b/libstdc++-v3/testsuite/tr1/2_general_utilities/shared_ptr/cons/43820_neg.cc
@@ -32,8 +32,8 @@ void test01()
 {
   X* px = 0;
   std::tr1::shared_ptr<X> p1(px);   // { dg-error "here" }
-  // { dg-error "incomplete" "" { target *-*-* } 556 }
+  // { dg-error "incomplete" "" { target *-*-* } 554 }
 
   std::tr1::shared_ptr<X> p9(ap());  // { dg-error "here" }
-  // { dg-error "incomplete" "" { target *-*-* } 595 }
+  // { dg-error "incomplete" "" { target *-*-* } 593 }
 }