re PR c/69407 (-Wunused-value on __atomic_fetch_OP and __atomic_OP_fetch)

	PR c/69407
	* c-common.c (resolve_overloaded_builtin): Set TREE_USED for the fetch
	operations.

	* gcc.dg/atomic-op-6.c: New test.

From-SVN: r234304

gcc/c-family/ChangeLog

+2016-03-17  Marek Polacek  <polacek@redhat.com>
+
+	PR c/69407
+	* c-common.c (resolve_overloaded_builtin): Set TREE_USED for the fetch
+	operations.
+
 2016-03-14  Jason Merrill  <jason@redhat.com>
 
 	* c-cppbuiltin.c (c_cpp_builtins): Set __cpp_hex_float.

gcc/c-family/c-common.c

@@ -11445,6 +11445,10 @@ resolve_overloaded_builtin (location_t loc, tree function,
 	    && orig_code != BUILT_IN_ATOMIC_STORE_N)
 	  result = sync_resolve_return (first_param, result, orig_format);
 
+	if (fetch_op)
+	  /* Prevent -Wunused-value warning.  */
+	  TREE_USED (result) = true;
+
 	/* If new_return is set, assign function to that expr and cast the
 	   result to void since the generic interface returned void.  */
 	if (new_return)

gcc/testsuite/ChangeLog

+2016-03-17  Marek Polacek  <polacek@redhat.com>
+
+	PR c/69407
+	* gcc.dg/atomic-op-6.c: New test.
+
 2016-03-17  David Malcolm  <dmalcolm@redhat.com>
 
 	PR c/70264

gcc/testsuite/gcc.dg/atomic-op-6.c

+/* Test we don't generate bogus warnings.  */
+/* PR c/69407 */
+/* { dg-do compile } */
+/* { dg-options "-Wall -Wextra" } */
+
+void
+foo (int *p, int a)
+{
+  __atomic_fetch_add (&p, a, 0); /* { dg-bogus "value computed is not used" } */
+  __atomic_add_fetch (&p, a, 0); /* { dg-bogus "value computed is not used" } */
+}