[gcc r12-7548] c++: Wrong error with alias template in class tmpl [PR104108]

[Marek Polacek <mpolacek@gcc.gnu.org>]

https://gcc.gnu.org/g:d54ce4641ed106666208be36fd514cae8ff1153c

commit r12-7548-gd54ce4641ed106666208be36fd514cae8ff1153c
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Mar 8 13:55:15 2022 -0500

    c++: Wrong error with alias template in class tmpl [PR104108]
    
    In r10-6329 I tried to optimize the number of calls to v_d_e_p in
    convert_nontype_argument by remembering whether the expression was
    value-dependent in a bool flag.  I did that wrongly assuming that its
    value-dependence will not be changed by build_converted_constant_expr.
    This testcase shows that it can: b_c_c_e gets a VAR_DECL for m_parameter,
    which is not value-dependent, but we're converting it to "const int &"
    so it returns
    
      (const int &)(const int *) &m_parameter
    
    which suddenly becomes value-dependent because of the added ADDR_EXPR:
    has_value_dependent_address is now true because m_parameter's context S<T>
    is dependent.  With this bug in place, we went to the second branch here:
    
          if (TYPE_REF_OBJ_P (TREE_TYPE (expr)) && val_dep_p)
            /* OK, dependent reference.  We don't want to ask whether a DECL is
               itself value-dependent, since what we want here is its address.  */;
          else
            {
              expr = build_address (expr);
    
              if (invalid_tparm_referent_p (type, expr, complain))
                return NULL_TREE;
            }
    
    wherein build_address created a bad tree and then i_t_r_p complained.
    
            PR c++/104108
    
    gcc/cp/ChangeLog:
    
            * pt.cc (convert_nontype_argument): Recompute
            value_dependent_expression_p after build_converted_constant_expr.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp0x/alias-decl-74.C: New test.

Diff:
---
 gcc/cp/pt.cc                               | 4 +++-
 gcc/testsuite/g++.dg/cpp0x/alias-decl-74.C | 9 +++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index c350ebb0a79..d47483dd4f2 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -7316,7 +7316,7 @@ convert_nontype_argument (tree type, tree expr, tsubst_flags_t complain)
   if (non_dep)
     expr = instantiate_non_dependent_expr_internal (expr, complain);
 
-  const bool val_dep_p = value_dependent_expression_p (expr);
+  bool val_dep_p = value_dependent_expression_p (expr);
   if (val_dep_p)
     expr = canonicalize_expr_argument (expr, complain);
   else
@@ -7357,6 +7357,8 @@ convert_nontype_argument (tree type, tree expr, tsubst_flags_t complain)
 	  expr = maybe_constant_value (expr, NULL_TREE,
 				       /*manifestly_const_eval=*/true);
 	  expr = convert_from_reference (expr);
+	  /* EXPR may have become value-dependent.  */
+	  val_dep_p = value_dependent_expression_p (expr);
 	}
       else if (TYPE_PTR_OR_PTRMEM_P (type))
 	{
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-74.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-74.C
new file mode 100644
index 00000000000..8382d856382
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-74.C
@@ -0,0 +1,9 @@
+// PR c++/104108
+// { dg-do compile { target c++11 } }
+
+template<template<const int&> class T>
+struct S {
+  static int m_parameter;
+  template<template<const int&> class TT>
+  using U = TT<m_parameter>;
+};