From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <jakub@sourceware.org>
Received: by sourceware.org (Postfix, from userid 2153)
 id 127C5385842E; Mon, 24 Jan 2022 09:21:23 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 127C5385842E
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset="utf-8"
From: Jakub Jelinek <jakub@gcc.gnu.org>
To: gcc-cvs@gcc.gnu.org
Subject: [gcc r11-9501] c++: Silence -Wuseless-cast warnings during move
 [PR103480]
X-Act-Checkin: gcc
X-Git-Author: Jakub Jelinek <jakub@redhat.com>
X-Git-Refname: refs/heads/releases/gcc-11
X-Git-Oldrev: 777b73e45983b11e010bd5192185ad01af444de4
X-Git-Newrev: cb4998fcdf2ad92fc6323fc4d9bc03299ca8a541
Message-Id: <20220124092123.127C5385842E@sourceware.org>
Date: Mon, 24 Jan 2022 09:21:23 +0000 (GMT)
X-BeenThere: gcc-cvs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-cvs mailing list <gcc-cvs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-cvs>,
 <mailto:gcc-cvs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-cvs/>
List-Help: <mailto:gcc-cvs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-cvs>,
 <mailto:gcc-cvs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Mon, 24 Jan 2022 09:21:23 -0000

https://gcc.gnu.org/g:cb4998fcdf2ad92fc6323fc4d9bc03299ca8a541

commit r11-9501-gcb4998fcdf2ad92fc6323fc4d9bc03299ca8a541
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Jan 12 09:47:46 2022 +0100

    c++: Silence -Wuseless-cast warnings during move [PR103480]
    
    This is maybe just a shot in the dark, but IMHO we shouldn't be diagnosing
    -Wuseless-cast on casts the compiler adds on its own when calling its move
    function.  We don't seem to warn when user calls std::move either.
    We call move on elinit (*NON_LVALUE_EXPR <(struct C[2] &&) &D.2497->b>)[0]
    so it is already an xvalue_p and try to static_cast it to struct C &&.
    But we don't warn e.g. on std::move (std::move (whatever)).
    
    Fixed by not doing the static cast and just returning expr from move
    if expr is already an xvalue.
    
    2022-01-11  Jakub Jelinek  <jakub@redhat.com>
                Jason Merrill  <jason@redhat.com>
    
            PR c++/103480
            * tree.c (move): If expr is xvalue_p, just return expr without
            build_static_cast.
    
            * g++.dg/warn/Wuseless-cast2.C: New test.
    
    (cherry picked from commit 6bba184ccbf47368eaea27ee2c1e7b850526640b)

Diff:
---
 gcc/cp/tree.c                              |  2 ++
 gcc/testsuite/g++.dg/warn/Wuseless-cast2.C | 24 ++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index 5c445b51e3f..306f61f719e 100644
--- a/gcc/cp/tree.c
+++ b/gcc/cp/tree.c
@@ -1275,6 +1275,8 @@ move (tree expr)
 {
   tree type = TREE_TYPE (expr);
   gcc_assert (!TYPE_REF_P (type));
+  if (xvalue_p (expr))
+    return expr;
   type = cp_build_reference_type (type, /*rval*/true);
   return build_static_cast (input_location, type, expr,
 			    tf_warning_or_error);
diff --git a/gcc/testsuite/g++.dg/warn/Wuseless-cast2.C b/gcc/testsuite/g++.dg/warn/Wuseless-cast2.C
new file mode 100644
index 00000000000..22e403973e7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wuseless-cast2.C
@@ -0,0 +1,24 @@
+// PR c++/103480
+// { dg-do compile { target c++14 } }
+// { dg-options "-Wuseless-cast" }
+
+template <typename T, int N>
+struct A { typedef T t[N]; };
+template <typename T, int N>
+struct B { typename A<T, N>::t b; };
+struct C {
+  constexpr C (C &&) {}
+  template <int N>
+  static auto bar ()
+  {
+    B<C, N> r;
+    return r;		// { dg-bogus "useless cast to type" }
+  }
+  C () = default;
+};
+
+void
+foo ()
+{
+  C::bar<2> ();
+}