On 6/29/26 4:38 AM, Jakub Jelinek wrote:
Hi!
https://eel.is/c++draft/class.prop#8.2 says that implicit lifetime
class shall have at least one trivial eligible constructor.
We currently walk all ctors and if it is default/copy/move ctor
which is trivial and not deleted, return true, but as the following testcase
shows, we should check also for unsatisfied constraints.
I wonder about adding an eligible_special_function_p function, though it
couldn't check the "more constrained" condition and would need to refer
to add_method's handling of that.
Let's also add a quote comment here of the section you link to above.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2026-06-29 Jakub Jelinek <[email protected]>
PR c++/126007
* tree.cc (implicit_lifetime_type_p): Check if trivial default
ctor, copy ctor or move ctor has satisfied constraints.
* g++.dg/ext/is_implicit_lifetime3.C: New test.
--- gcc/cp/tree.cc.jj 2026-06-25 10:03:50.818436378 +0200
+++ gcc/cp/tree.cc 2026-06-27 11:46:17.353081353 +0200
@@ -4955,6 +4955,7 @@ implicit_lifetime_type_p (tree t)
fn = *iter;
if ((default_ctor_p (fn) || copy_fn_p (fn) || move_fn_p (fn))
&& trivial_fn_p (fn)
+ && constraints_satisfied_p (fn)
&& !DECL_DELETED_FN (fn))
return true;
}
--- gcc/testsuite/g++.dg/ext/is_implicit_lifetime3.C.jj 2026-06-27
11:49:33.102692105 +0200
+++ gcc/testsuite/g++.dg/ext/is_implicit_lifetime3.C 2026-06-27
11:50:38.106905466 +0200
@@ -0,0 +1,11 @@
+// PR c++/126007
+// { dg-do compile { target c++20 } }
+
+template <bool B>
+struct S {
+ S () requires B = default;
+ S (const S &) {}
+};
+
+static_assert (!__builtin_is_implicit_lifetime (S<false>));
+static_assert (__builtin_is_implicit_lifetime (S<true>));
Jakub
