re PR c++/85952 (Bogus -Wunused-but-set-variable warning with array structured binding)

PR c++/85952
	* init.c (build_aggr_init): For structured binding initialized from
	array call mark_rvalue_use on the initializer.

	* g++.dg/warn/Wunused-var-33.C: New test.

From-SVN: r260899

gcc/cp/ChangeLog

@@ -1,3 +1,9 @@
+2018-05-29  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/85952
+	* init.c (build_aggr_init): For structured binding initialized from
+	array call mark_rvalue_use on the initializer.
+
 2018-05-28  Bernd Edlinger  <bernd.edlinger@hotmail.de>
 
 	* decl2.c (start_static_storage_duration_function): Use

gcc/cp/init.c

@@ -1678,6 +1678,7 @@ build_aggr_init (tree exp, tree init, int flags, tsubst_flags_t complain)
       if (VAR_P (exp) && DECL_DECOMPOSITION_P (exp))
 	{
 	  from_array = 1;
+	  init = mark_rvalue_use (init);
 	  if (init && DECL_P (init)
 	      && !(flags & LOOKUP_ONLYCONVERTING))
 	    {

gcc/testsuite/ChangeLog

@@ -1,5 +1,8 @@
 2018-05-29  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/85952
+	* g++.dg/warn/Wunused-var-33.C: New test.
+
 	PR target/85918
 	* gcc.target/i386/avx512dq-pr85918.c: Add -mprefer-vector-width=512
 	and -fno-vect-cost-model options.  Add aligned(64) attribute to the

gcc/testsuite/g++.dg/warn/Wunused-var-33.C

@@ -0,0 +1,37 @@
+// PR c++/85952
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wunused-but-set-variable" }
+
+int
+foo ()
+{
+  int a[2] = {1, 2};	// { dg-bogus "set but not used" } */
+  auto [x, y] = a;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return x + y;
+}
+
+struct S { int d, e; };
+
+int
+bar ()
+{
+  S a = {1, 2};
+  auto [x, y] = a;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return x + y;
+}
+
+int
+baz ()
+{
+  S a = {1, 2};
+  auto & [x, y] = a;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return x + y;
+}
+
+int
+qux ()
+{
+  int a[2] = {1, 2};
+  auto & [x, y] = a;	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+  return x + y;
+}