c++: __is_trivially_xible and multi-arg aggr paren init [PR102535]

is_xible_helper assumes only 0- and 1-argument ctors can be trivial, but
C++20 aggregate paren init means multi-arg ctors can now be trivial too.
This patch relaxes the relevant early exit check accordingly.

	PR c++/102535

gcc/cp/ChangeLog:

	* method.c (is_xible_helper): Don't exit early for multi-arg
	ctors in C++20.

gcc/testsuite/ChangeLog:

	* g++.dg/ext/is_trivially_constructible7.C: New test.

diff --git a/gcc/cp/method.c b/gcc/cp/method.c
index 3c34952..c38912a 100644 (file)
--- a/gcc/cp/method.c
+++ b/gcc/cp/method.c
@@ -2094,8 +2094,10 @@ is_xible_helper (enum tree_code code, tree to, tree from, bool trivial)
   tree expr;
   if (code == MODIFY_EXPR)
     expr = assignable_expr (to, from);
-  else if (trivial && from && TREE_CHAIN (from))
+  else if (trivial && from && TREE_CHAIN (from)
+          && cxx_dialect < cxx20)
     return error_mark_node; // only 0- and 1-argument ctors can be trivial
+                           // before C++20 aggregate paren init
   else if (TREE_CODE (to) == ARRAY_TYPE && !TYPE_DOMAIN (to))
     return error_mark_node; // can't construct an array of unknown bound
   else

diff --git a/gcc/testsuite/g++.dg/ext/is_trivially_constructible7.C b/gcc/testsuite/g++.dg/ext/is_trivially_constructible7.C
new file mode 100644 (file)
index 0000000..f6fbf8f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_trivially_constructible7.C
@@ -0,0 +1,17 @@
+// PR c++/102535
+// Verify __is_trivially_constructible works with multi-arg paren init of
+// aggrs.
+
+struct A { int x; };
+struct B { float y; };
+struct C { char z; };
+struct D { A a; B b; C c; };
+
+extern int n[1 + __is_trivially_constructible(D, A)];
+extern int n[1 + __is_trivially_constructible(D, A, B)];
+extern int n[1 + __is_trivially_constructible(D, A, B, C)];
+#if __cpp_aggregate_paren_init
+extern int n[1 + true];
+#else
+extern int n[1 + false];
+#endif