PR c/68868 - atomic_init emits an unnecessary fence

gcc/ChangeLog
	* ginclude/stdatomic.h (atomic_init): Use atomic_store instead
	of plain assignment.
gcc/testsuite/ChangeLog
	* testsuite/gcc.dg/atomic/stdatomic-init.c: New test.

From-SVN: r231733

gcc/ChangeLog

+2015-12-16  Martin Sebor  <msebor@redhat.com>
+
+	PR c/68868
+	* ginclude/stdatomic.h (atomic_init): Use atomic_store instead
+	of plain assignment.
+
 2015-12-15  Michael Meissner  <meissner@linux.vnet.ibm.com>
 
 	PR target/68805

gcc/ginclude/stdatomic.h

@@ -77,12 +77,10 @@ typedef _Atomic __UINTMAX_TYPE__ atomic_uintmax_t;
 
 
 #define ATOMIC_VAR_INIT(VALUE)	(VALUE)
-#define atomic_init(PTR, VAL)			\
-  do						\
-    {						\
-      *(PTR) = (VAL);				\
-    }						\
-  while (0)
+
+/* Initialize an atomic object pointed to by PTR with VAL.  */
+#define atomic_init(PTR, VAL)                           \
+  atomic_store_explicit (PTR, VAL, __ATOMIC_RELAXED)
 
 #define kill_dependency(Y)			\
   __extension__					\

gcc/testsuite/ChangeLog

+2015-12-16  Martin Sebor  <msebor@redhat.com>
+
+	PR c/68868
+	* testsuite/gcc.dg/atomic/stdatomic-init.c: New test.
+
 2015-12-15  Michael Meissner  <meissner@linux.vnet.ibm.com>
 
 	PR target/68805

gcc/testsuite/gcc.dg/atomic/stdatomic-init.c

+/* Test the atomic_init generic function.  Verify that __atomic_store_N
+   is called with the last argument of memory_order_relaxed (i.e., 0)
+   for each invocation of the atomic_init() macro in the test and that
+   there are no calls to __atomic_store_N with a non-zero last argument.  */
+/* { dg-do compile } */
+/* { dg-options "-fdump-tree-gimple -std=c11 -pedantic-errors" } */
+/* { dg-final { scan-tree-dump-times "__atomic_store_. \\(\[^\n\r]*, 0\\)" 54 "gimple" } } */
+/* { dg-final { scan-tree-dump-not "__atomic_store_. \\(\[^\n\r]*, \[1-5\]\\)" "gimple" } } */
+
+#include <stdatomic.h>
+
+struct Atomic {
+  /* Volatile to prevent re-initialization from being optimized away.  */
+  volatile atomic_bool   b;
+  volatile atomic_char   c;
+  volatile atomic_schar  sc;
+  volatile atomic_uchar  uc;
+  volatile atomic_short  ss;
+  volatile atomic_ushort us;
+  volatile atomic_int    si;
+  volatile atomic_uint   ui;
+  volatile atomic_long   sl;
+  volatile atomic_ulong  ul;
+  volatile atomic_llong  sll;
+  volatile atomic_ullong ull;
+  volatile atomic_size_t sz;
+};
+
+struct Value {
+  _Bool              b;
+  char               c;
+  signed char        sc;
+  unsigned char      uc;
+  short              ss;
+  unsigned short     us;
+  int                si;
+  unsigned int       ui;
+  long               sl;
+  unsigned long      ul;
+  long long          sll;
+  unsigned long long ull;
+  __SIZE_TYPE__      sz;
+};
+
+/* Exercise the atomic_init() macro with a literal argument.  */
+
+void atomic_init_lit (struct Atomic *pa)
+{
+  atomic_init (&pa->b, 0);
+  atomic_init (&pa->b, 1);
+
+  atomic_init (&pa->c, 'x');
+  atomic_init (&pa->c, 0);
+  atomic_init (&pa->c, 1);
+  atomic_init (&pa->c, 255);
+  
+  atomic_init (&pa->sc, (signed char)'x');
+  atomic_init (&pa->sc, (signed char)0);
+  atomic_init (&pa->sc, (signed char)1);
+  atomic_init (&pa->sc, (signed char)__SCHAR_MAX__);
+
+  atomic_init (&pa->uc, (unsigned char)'x');
+  atomic_init (&pa->uc, (unsigned char)0);
+  atomic_init (&pa->uc, (unsigned char)1);
+  atomic_init (&pa->sc, (unsigned char)__SCHAR_MAX__);
+
+  atomic_init (&pa->ss, (signed short)0);
+  atomic_init (&pa->ss, (signed short)1);
+  atomic_init (&pa->ss, (signed short)__SHRT_MAX__);
+
+  atomic_init (&pa->us, (unsigned short)0);
+  atomic_init (&pa->us, (unsigned short)1);
+  atomic_init (&pa->us, (unsigned short)__SHRT_MAX__);
+
+  atomic_init (&pa->si, (signed int)0);
+  atomic_init (&pa->si, (signed int)1);
+  atomic_init (&pa->si, (signed int)__INT_MAX__);
+
+  atomic_init (&pa->ui, (unsigned int)0);
+  atomic_init (&pa->ui, (unsigned int)1);
+  atomic_init (&pa->ui, (unsigned int)__INT_MAX__);
+  
+  atomic_init (&pa->sl, (signed long)0);
+  atomic_init (&pa->sl, (signed long)1);
+  atomic_init (&pa->sl, (signed long)__LONG_MAX__);
+
+  atomic_init (&pa->ul, (unsigned long)0);
+  atomic_init (&pa->ul, (unsigned long)1);
+  atomic_init (&pa->ul, (unsigned long)__LONG_MAX__);
+
+  atomic_init (&pa->sll, (signed long long)0);
+  atomic_init (&pa->sll, (signed long long)1);
+  atomic_init (&pa->sll, (signed long long)__LONG_LONG_MAX__);
+
+  atomic_init (&pa->ull, (unsigned long long)0);
+  atomic_init (&pa->ull, (unsigned long long)1);
+  atomic_init (&pa->ull, (unsigned long long)__LONG_LONG_MAX__); 
+
+  atomic_init (&pa->sz, 0);
+  atomic_init (&pa->sz, 1);
+  atomic_init (&pa->sz, __SIZE_MAX__); 
+}
+
+/* Exercise the atomic_init() macro with an lvalue argument.  */
+
+void atomic_init_lval (struct Atomic *pa, const struct Value *pv)
+{
+  atomic_init (&pa->b, pv->b);
+  atomic_init (&pa->c, pv->c);
+  atomic_init (&pa->sc, pv->sc);
+  atomic_init (&pa->uc, pv->uc);
+  atomic_init (&pa->ss, pv->ss);
+  atomic_init (&pa->us, pv->us);
+  atomic_init (&pa->si, pv->si);
+  atomic_init (&pa->ui, pv->ui); 
+  atomic_init (&pa->sl, pv->sl);
+  atomic_init (&pa->ul, pv->ul);
+  atomic_init (&pa->sll, pv->sll);
+  atomic_init (&pa->ull, pv->ull);
+  atomic_init (&pa->sz, pv->sz);
+}