[gcc r12-7789] c++: tweak PR103337 fix

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

https://gcc.gnu.org/g:2cd0c9a5310420e1039be5e514a818b6d381d89f

commit r12-7789-g2cd0c9a5310420e1039be5e514a818b6d381d89f
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Mar 23 13:22:25 2022 -0400

    c++: tweak PR103337 fix
    
    Patrick suggested a way to implement the designated-init handling without
    (temporarily) modifying the CONSTRUCTOR being reshaped.
    
            PR c++/103337
    
    gcc/cp/ChangeLog:
    
            * decl.cc (reshape_single_init): New.
            (reshape_init_class): Use it.

Diff:
---
 gcc/cp/decl.cc | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 34d9dad9fb0..efef1b7370f 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -6543,6 +6543,21 @@ reshape_init_vector (tree type, reshape_iter *d, tsubst_flags_t complain)
 			       NULL_TREE, complain);
 }
 
+/* Subroutine of reshape_init*: We're initializing an element with TYPE from
+   INIT, in isolation from any designator or other initializers.  */
+
+static tree
+reshape_single_init (tree type, tree init, tsubst_flags_t complain)
+{
+  /* We could also implement this by wrapping init in a new CONSTRUCTOR and
+     calling reshape_init, but this way can just live on the stack.  */
+  constructor_elt elt = { /*index=*/NULL_TREE, init };
+  reshape_iter iter = { &elt, &elt + 1 };
+  return reshape_init_r (type, &iter,
+			 /*first_initializer_p=*/NULL_TREE,
+			 complain);
+}
+
 /* Subroutine of reshape_init_r, processes the initializers for classes
    or union. Parameters are the same of reshape_init_r.  */
 
@@ -6690,24 +6705,19 @@ reshape_init_class (tree type, reshape_iter *d, bool first_initializer_p,
 
       if (direct_desig)
 	{
-	  /* The designated field F is initialized from this one element:
-	     Temporarily clear the designator so a recursive reshape_init_class
-	     doesn't try to find it again in F, and adjust d->end so we don't
-	     try to use the next initializer to initialize another member of F.
+	  /* The designated field F is initialized from this one element.
 
-	     Note that we don't want these changes if we found the designator
-	     inside an anon aggr above; we leave them alone to implement:
+	     Note that we don't want to do this if we found the designator
+	     inside an anon aggr above; we use the normal code to implement:
 
 	     "If the element is an anonymous union member and the initializer
 	     list is a brace-enclosed designated- initializer-list, the element
 	     is initialized by the designated-initializer-list { D }, where D
 	     is the designated- initializer-clause naming a member of the
 	     anonymous union member."  */
-	  auto end_ = make_temp_override (d->end, d->cur + 1);
-	  auto idx_ = make_temp_override (d->cur->index, NULL_TREE);
-	  field_init = reshape_init_r (TREE_TYPE (field), d,
-				       /*first_initializer_p=*/NULL_TREE,
-				       complain);
+	  field_init = reshape_single_init (TREE_TYPE (field),
+					    d->cur->value, complain);
+	  d->cur++;
 	}
       else
 	field_init = reshape_init_r (TREE_TYPE (field), d,