[gcc r14-4231] c++ __integer_pack conversion again [PR111357]

[Jason Merrill]

https://gcc.gnu.org/g:fd35d72a3dcd5ba14d81a1890236acd0145497e1

commit r14-4231-gfd35d72a3dcd5ba14d81a1890236acd0145497e1
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Sep 21 15:39:46 2023 +0100

    c++ __integer_pack conversion again [PR111357]
    
    As Jakub pointed out, the real problem here is that in a partial
    substitution we're forgetting the conversion to the type of the non-type
    template argument, because maybe_convert_nontype_argument doesn't do
    anything with value-dependent arguments.  I'm experimenting with changing
    that, but in the meantime we can work around it here.
    
            PR c++/111357
    
    gcc/cp/ChangeLog:
    
            * pt.cc (expand_integer_pack): Use IMPLICIT_CONV_EXPR.

Diff:
---
 gcc/cp/pt.cc | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index ea5379098a5..73ac1cb597c 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -3769,6 +3769,13 @@ expand_integer_pack (tree call, tree args, tsubst_flags_t complain,
     {
       if (hi != ohi)
 	{
+	  /* Work around maybe_convert_nontype_argument not doing this for
+	     dependent arguments.  Don't use IMPLICIT_CONV_EXPR_NONTYPE_ARG
+	     because that will make tsubst_copy_and_build ignore it.  */
+	  tree type = tsubst (TREE_TYPE (ohi), args, complain, in_decl);
+	  if (!TREE_TYPE (hi) || !same_type_p (type, TREE_TYPE (hi)))
+	    hi = build1 (IMPLICIT_CONV_EXPR, type, hi);
+
 	  call = copy_node (call);
 	  CALL_EXPR_ARG (call, 0) = hi;
 	}
@@ -3779,8 +3786,6 @@ expand_integer_pack (tree call, tree args, tsubst_flags_t complain,
     }
   else
     {
-      hi = perform_implicit_conversion_flags (integer_type_node, hi, complain,
-					      LOOKUP_IMPLICIT);
       hi = instantiate_non_dependent_expr (hi, complain);
       hi = cxx_constant_value (hi, complain);
       int len = valid_constant_size_p (hi) ? tree_to_shwi (hi) : -1;