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From: "mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107797] "warning right operand of comma operator has no
 effect" for expressions with no comma operator
Date: Thu, 19 Jan 2023 19:03:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107797

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot=
 gnu.org
             Status|NEW                         |ASSIGNED

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
This seems to work:

diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
index 0cbfd8060cb..d1e34d7de1a 100644
--- a/gcc/cp/cvt.cc
+++ b/gcc/cp/cvt.cc
@@ -711,8 +711,11 @@ ocp_convert (tree type, tree expr, int convtype, int
flags,
    return error_mark_node;
       if (e =3D=3D TREE_OPERAND (expr, 1))
    return expr;
-      return build2_loc (EXPR_LOCATION (expr), COMPOUND_EXPR, TREE_TYPE (e=
),
-            TREE_OPERAND (expr, 0), e);
+      e =3D build2_loc (EXPR_LOCATION (expr), COMPOUND_EXPR, TREE_TYPE (e),
+             TREE_OPERAND (expr, 0), e);
+      if (warning_suppressed_p (expr, OPT_Wunused_value))
+   suppress_warning (e, OPT_Wunused_value);
+      return e;
     }

   complete_type (type);
diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index f816c474cef..52e96fbe590 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -3800,6 +3800,8 @@ build_new_1 (vec<tree, va_gc> **placement, tree type,
tree nelts,
   if (cookie_expr)
     rval =3D build2 (COMPOUND_EXPR, TREE_TYPE (rval), cookie_expr, rval);

+  suppress_warning (rval, OPT_Wunused_value);
+
   if (rval =3D=3D data_addr && TREE_CODE (alloc_expr) =3D=3D TARGET_EXPR)
     /* If we don't have an initializer or a cookie, strip the TARGET_EXPR
        and return the call (which doesn't need to be adjusted).  */=