[gcc r16-2691] c++: constexpr, array, private ctor [PR120800]

[Jason Merrill via Gcc-cvs]

https://gcc.gnu.org/g:f6462f664725844faa97ae7e8690e4fedee65788

commit r16-2691-gf6462f664725844faa97ae7e8690e4fedee65788
Author: Jason Merrill <ja...@redhat.com>
Date:   Thu Jul 31 14:23:10 2025 -0400

    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.

Diff:
---
 gcc/cp/constexpr.cc                            |  3 +++
 gcc/testsuite/g++.dg/cpp0x/constexpr-array30.C | 22 ++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index e051a50fe16e..be24ae2feda6 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -6598,6 +6598,9 @@ 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, jump_target);
 
+  /* 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 000000000000..3f724072e83e
--- /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;