[gcc r13-5611] c++: aggregate base and TARGET_EXPR_ELIDING_P [PR108559]

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:b533084d756a2696a3eb6521810e0a0b2182a8e8

commit r13-5611-gb533084d756a2696a3eb6521810e0a0b2182a8e8
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Jan 30 18:18:54 2023 -0500

    c++: aggregate base and TARGET_EXPR_ELIDING_P [PR108559]
    
    We also need to split up a CONSTRUCTOR in cp_genericize_init if we need to
    add extra copy constructor calls to deal with CWG2403.
    
            PR c++/108559
    
    gcc/cp/ChangeLog:
    
            * cp-gimplify.cc (any_non_eliding_target_exprs): New.
            (cp_genericize_init): Check it.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp1z/aggr-base13.C: New test.

Diff:
---
 gcc/cp/cp-gimplify.cc                    | 22 +++++++++++++++++++---
 gcc/testsuite/g++.dg/cpp1z/aggr-base13.C | 19 +++++++++++++++++++
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index a35cedd05cc..9929d29981a 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -893,6 +893,21 @@ omp_cxx_notice_variable (struct cp_genericize_omp_taskreg *omp_ctx, tree decl)
     }
 }
 
+/* True if any of the element initializers in CTOR are TARGET_EXPRs that are
+   not expected to elide, e.g. because unsafe_copy_elision_p is true.  */
+
+static bool
+any_non_eliding_target_exprs (tree ctor)
+{
+  for (const constructor_elt &e : *CONSTRUCTOR_ELTS (ctor))
+    {
+      if (TREE_CODE (e.value) == TARGET_EXPR
+	  && !TARGET_EXPR_ELIDING_P (e.value))
+	return true;
+    }
+  return false;
+}
+
 /* If we might need to clean up a partially constructed object, break down the
    CONSTRUCTOR with split_nonconstant_init.  Also expand VEC_INIT_EXPR at this
    point.  If initializing TO with FROM is non-trivial, overwrite *REPLACE with
@@ -904,10 +919,11 @@ cp_genericize_init (tree *replace, tree from, tree to)
   tree init = NULL_TREE;
   if (TREE_CODE (from) == VEC_INIT_EXPR)
     init = expand_vec_init_expr (to, from, tf_warning_or_error);
-  else if (flag_exceptions
-	   && TREE_CODE (from) == CONSTRUCTOR
+  else if (TREE_CODE (from) == CONSTRUCTOR
 	   && TREE_SIDE_EFFECTS (from)
-	   && TYPE_HAS_NONTRIVIAL_DESTRUCTOR (TREE_TYPE (from)))
+	   && ((flag_exceptions
+		&& TYPE_HAS_NONTRIVIAL_DESTRUCTOR (TREE_TYPE (from)))
+	       || any_non_eliding_target_exprs (from)))
     {
       to = cp_stabilize_reference (to);
       replace_placeholders (from, to);
diff --git a/gcc/testsuite/g++.dg/cpp1z/aggr-base13.C b/gcc/testsuite/g++.dg/cpp1z/aggr-base13.C
new file mode 100644
index 00000000000..c4c7ee0e8f0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/aggr-base13.C
@@ -0,0 +1,19 @@
+// PR c++/108559
+// { dg-do compile { target c++17 } }
+
+struct A {
+  int g = 0;
+
+  A() {}
+  A(const A&) {}
+};
+
+struct B : A {};
+
+A u() { return A{}; }
+
+int bug() { return B{u()}.g; }
+
+int main() {
+  return 0;
+}