From df63b4a2f77acd6d10aad68fdfbf4d5b698dad5b Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Thu, 31 Jul 2025 14:23:31 -0400
Subject: [PATCH] c++: constexpr, array, private ctor [PR120800]

Here cxx_eval_vec_init_1 wants to recreate the default constructor call that
we previously built and threw away in build_vec_init_elt, but we aren't in
the same access context at this point.  Since we already checked access,
let's just suppress access control here.

Redoing overload resolution at constant evaluation time is sketchy, but
should usually be fine for a default/copy constructor.

	PR c++/120800

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_eval_vec_init_1): Suppress access control.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/constexpr-array30.C: New test.

(cherry picked from commit f6462f664725844faa97ae7e8690e4fedee65788)
---
 gcc/cp/constexpr.cc                           |  3 +++
 .../g++.dg/cpp0x/constexpr-array30.C          | 22 +++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-array30.C

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 18cc7339507..f6b9a808825 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -5654,6 +5654,9 @@ cxx_eval_vec_init_1 (const constexpr_ctx *ctx, tree atype, tree init,
     return cxx_eval_bare_aggregate (ctx, init, lval,
 				    non_constant_p, overflow_p);
 
+  /* We already checked access when building the VEC_INIT_EXPR.  */
+  deferring_access_check_sentinel acs (dk_deferred);
+
   /* For the default constructor, build up a call to the default
      constructor of the element type.  We only need to handle class types
      here, as for a constructor to be constexpr, all members must be
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-array30.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-array30.C
new file mode 100644
index 00000000000..3f724072e83
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-array30.C
@@ -0,0 +1,22 @@
+// PR c++/120800
+// { dg-do compile { target c++11 } }
+
+template<typename T>
+struct Container
+{
+ T m_data[1] {};
+};
+
+class Element
+{
+private:
+ Element() = default;
+
+private:
+ bool m_bool1 { false };
+ bool m_bool2;
+
+ friend struct Container<Element>;
+};
+
+Container<Element> element;
-- 
2.47.2