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https://gcc.gnu.org/PR100644
https://bugs.gentoo.org/792705
From 6384e940a6db379b0524465cf6cbbd0996b48485 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Tue, 18 May 2021 12:06:36 -0400
Subject: [PATCH] c++: "perfect" implicitly deleted move [PR100644]
Here we were ignoring the template constructor because the implicit move
constructor had all perfect conversions. But CWG1402 says that an
implicitly deleted move constructor is ignored by overload resolution; we
implement that instead by preferring any other candidate in joust, to get
better diagnostics, but that means we need to handle that case here as well.
gcc/cp/ChangeLog:
PR c++/100644
* call.c (perfect_candidate_p): An implicitly deleted move
is not perfect.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/implicit-delete1.C: New test.
---
gcc/cp/call.c | 5 +++++
gcc/testsuite/g++.dg/cpp0x/implicit-delete1.C | 20 +++++++++++++++++++
2 files changed, 25 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/implicit-delete1.C
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -5892,6 +5892,11 @@ perfect_candidate_p (z_candidate *cand)
{
if (cand->viable < 1)
return false;
+ /* CWG1402 makes an implicitly deleted move op worse than other
+ candidates. */
+ if (DECL_DELETED_FN (cand->fn) && DECL_DEFAULTED_FN (cand->fn)
+ && move_fn_p (cand->fn))
+ return false;
int len = cand->num_convs;
for (int i = 0; i < len; ++i)
if (!perfect_conversion_p (cand->convs[i]))
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/implicit-delete1.C
@@ -0,0 +1,20 @@
+// PR c++/100644
+// { dg-do compile { target c++11 } }
+
+struct NonMovable {
+ NonMovable(NonMovable&&) = delete;
+};
+
+template <class T>
+struct Maybe {
+ NonMovable mMember;
+
+ template <typename U>
+ Maybe(Maybe<U>&&);
+};
+
+void foo(Maybe<int>);
+
+void unlucky(Maybe<int>&& x) {
+ Maybe<int> var{(Maybe<int>&&)x};
+}
--
2.31.1
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