2019-08-30  Jakub Jelinek  <jakub@redhat.com>

	Backported from mainline
	2019-03-26  Jakub Jelinek  <jakub@redhat.com>

	PR c++/89796
	* semantics.c (finish_omp_atomic): Add warning_sentinel for
	-Wunused-value around finish_expr_stmt call.

	* g++.dg/gomp/pr89796.C: New test.
	* gcc.dg/gomp/pr89796.c: New test.

--- gcc/cp/semantics.c	(revision 270740)
+++ gcc/cp/semantics.c	(revision 270741)
@@ -8462,6 +8462,11 @@ finish_omp_atomic (enum tree_code code,
       stmt = build2 (OMP_ATOMIC, void_type_node, integer_zero_node, stmt);
       OMP_ATOMIC_SEQ_CST (stmt) = seq_cst;
     }
+
+  /* Avoid -Wunused-value warnings here, the whole construct has side-effects
+     and even if it might be wrapped from fold-const.c or c-omp.c wrapped
+     in some tree that appears to be unused, the value is not unused.  */
+  warning_sentinel w (warn_unused_value);
   finish_expr_stmt (stmt);
 }
 
--- gcc/testsuite/gcc.dg/gomp/pr89796.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/gomp/pr89796.c	(revision 270741)
@@ -0,0 +1,23 @@
+/* PR c++/89796 */
+/* { dg-do compile } */
+/* { dg-additional-options "-Wunused-value" } */
+
+int
+f1 (int *p)
+{
+  int r;
+  #pragma omp atomic capture		/* { dg-bogus "value computed is not used" } */
+  { r = *p; (*p)++; }
+  return r;
+}
+
+int
+f2 (int *p)
+{
+  int s
+    = ({ int r;
+	 #pragma omp atomic capture	/* { dg-bogus "value computed is not used" } */
+	 { r = *p; (*p)++; }
+	 r; });
+  return s;
+}
--- gcc/testsuite/g++.dg/gomp/pr89796.C	(nonexistent)
+++ gcc/testsuite/g++.dg/gomp/pr89796.C	(revision 270741)
@@ -0,0 +1,53 @@
+// PR c++/89796
+// { dg-do compile }
+// { dg-additional-options "-Wunused-value" }
+
+int
+f1 (int &c)
+{
+  int r;
+  #pragma omp atomic capture	// { dg-bogus "value computed is not used" }
+  { r = c; c++; }
+  return r;
+}
+
+template <int N>
+int
+f2 (int &c)
+{
+  int r;
+  #pragma omp atomic capture	// { dg-bogus "value computed is not used" }
+  { r = c; c++; }
+  return r;
+}
+
+int
+f3 (int &c)
+{
+  return f2 <0> (c);
+}
+
+int
+f4 (int *p)
+{
+  int r;
+  #pragma omp atomic capture	// { dg-bogus "value computed is not used" }
+  { r = *p; (*p)++; }
+  return r;
+}
+
+template <int N>
+int
+f5 (int *p)
+{
+  int r;
+  #pragma omp atomic capture	// { dg-bogus "value computed is not used" }
+  { r = *p; (*p)++; }
+  return r;
+}
+
+int
+f6 (int *p)
+{
+  return f5 <0> (p);
+}