[Bug c++/85695] [8/9 Regression] if constexpr misevaluates typedefed type value

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85695

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This fixes it:

--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -736,7 +736,7 @@ finish_if_stmt_cond (tree cond, tree if_stmt)
       && !instantiation_dependent_expression_p (cond)
       /* Wait until instantiation time, since only then COND has been
         converted to bool.  */
-      && TREE_TYPE (cond) == boolean_type_node)
+      && strip_typedefs (TREE_TYPE (cond)) == boolean_type_node)
     {
       cond = instantiate_non_dependent_expr (cond);
       cond = cxx_constant_value (cond, NULL_TREE);