https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93676
--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
We might get away with just avoiding value-init in a template:
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -4520,7 +4520,7 @@ build_vec_init (tree base, tree maxindex, tree init,
We do need to keep going if we're copying an array. */
- if (try_const && !init)
+ if (try_const && !init && !processing_template_decl)
/* With a constexpr default constructor, which we checked for when
setting try_const above, default-initialization is equivalent to
value-initialization, and build_value_init gives us something more
testing more...
