Patchwork Require canonical type comparison for typedefs again.

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Submitter Dodji Seketeli
Date Oct. 6, 2010, 6:52 p.m.
Message ID <m3zkurw3us.fsf@redhat.com>
Download mbox | patch
Permalink /patch/66961/
State New
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Comments

Dodji Seketeli - Oct. 6, 2010, 6:52 p.m.
Hello,

Following your comments here is a new version of the patch.

The main changes are the following:

* the list of template parms is walked only once for the fixup.

* following our discussion offline I moved the sibbling parms number
  moved to TEMPLATE_PARM_INDEX. I created a new field in struct
  template_parm_index_s for that because I couldn't find another free
  slot. Maybe you'd have an idea to avoid adding this field here.

* to substitute fixed-up template type parameters into parameters of
  template template parameters, I tried hard to build the full set of
  template parameters to avoid triggering partial instantiation. E,g:

  template<class T> //#0
  struct S
  {
    template<template<class U, T a> class TPL> void foo(T t); // #1<-- here
  };

  When substituting the fixed up T of #0 into the a parameter in #1, I
  use the following set of template parms as argument to tsubst:
  {{T}, {TPL}, {U, T}}. This is similar to what is done in
  lookup_template_class when the D1 parameter of that function is a
  template template parm. This way I could do away with the
  tf_no_tpl_reduce flag I introduced in the previous version of the
  patch.

* when fixing up a template type parms T, make sure subsequent name
  lookups of T return the fixed up T. Not the pre-fixup one. That
  basically means that I set the TREE_TYPE of of the TYPE_NAME of the
  pre-fixup T to the fixedup T.

  I do a similar trick for non-type template parms too. E,g, consider this:

  template<class T, T u> //#0
  auto foo(T t) -> decltype(u); //#1

  After fixup, I want lookups of u at #1 to return references to the
  fixedup T, not to the pre-fixup one.

* canonical_type_parameter doesn't return NULL_TREE anymore.

Tested on x86_64-unknown-linux-gnu against trunk.
Paolo Carlini - Oct. 6, 2010, 10:16 p.m.
Hi,

> diff --git a/gcc/testsuite/g++.dg/template/typedef36.C b/gcc/testsuite/g++.dg/template/typedef36.C
> new file mode 100644
> index 0000000..f6155c1
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/typedef36.C
> @@ -0,0 +1,23 @@
> +// Origin: PR c++/45606
> +// { dg-do compile }
> +
> +#include <list>
> +
> +template<class T>
> +class Test
> +{
> +protected:
> +  typedef std::list<T> ListAlias;
> +  ListAlias list;
> +public:
> +  typedef typename ListAlias::const_iterator const_iterator;
> +  inline const_iterator begin() const;
> +
> +};
> +
> +template<class T>
> +inline typename std::list<T>::const_iterator Test<T>::begin() const
> +{
> +  return list.begin();
> +}
> +

Once again, if, thanks to the analysis you did to fix the problem, you are able to quickly figure out a shorter testcase, not including the entire <list>, I think it would be good.

Thanks,
Paolo
Jason Merrill - Oct. 7, 2010, 6:30 p.m.
This is shaping up well, but there are still some issues:

On 10/06/2010 02:52 PM, Dodji Seketeli wrote:
> -/* Contains canonical template parameter types. The vector is indexed by
> -   the TEMPLATE_TYPE_IDX of the template parameter. Each element is a
> -   TREE_LIST, whose TREE_VALUEs contain the canonical template
> -   parameters of various types and levels.  */
> +/* Contains canonical template parameter types. The vector is indexed
> +   by the TEMPLATE_TYPE_IDX of the template parameter. Each element is
> +   a TREE_LIST, whose TREE_PURPOSE is a INT_CST tree representing a
> +   total size of the template parameter list a given template
> +   parameter would belong too, and whose TREE_VALUEs contain the
> +   canonical template parameters of various types and levels,
> +   belonging to a set of template parameters which size is
> +   TREE_PURPOSE.  */

We don't really need to change the representation this way, do we?  We 
can just let structural_comptypes verify that the total parms # matches. 
  Same with the changes to canonical_type_parameter.

> +         if (TREE_PURPOSE (cur))
> +           {
> +             /* So the current template type parameter has a default
> +                argument. Substitute the so far fixed-up template
> +                parms into it.   */
> +             tree default_arg = TREE_PURPOSE (cur);
> +
> +             if (TYPE_P (default_arg)
> +                 && !dependent_type_p (default_arg))
> +               continue;
> +
> +             arglist = current_template_args ();

Why do we need to get current_template_args() again here?

> +             ++cp_unevaluated_operand;
> +             TREE_PURPOSE (cur) =
> +               tsubst_expr (default_arg, arglist,
> +                            tf_none, default_arg, false);
> +             --cp_unevaluated_operand;

tsubst (default_arg, arglist, tf_warning_or_error, parm);

And don't mess with cp_unevaluated_operand.

> +         /* Now we need to substitute the template parm types that
> +            have been fixed up so far into the non-type template
> +            parms of this template template parm. E.g, consider this:

This needs to be recursive, in case the template template parm has its 
own template template parms.

template <class T, template <template <class U = T> class V> class W> 
class A;

> +             ++cp_unevaluated_operand;
> +             substed_parm = tsubst_template_parm (parameter, targs, tf_none);
> +             --cp_unevaluated_operand;

Still shouldn't be messing with cp_unevaluated_operand.  And we should 
use tf_warning_or_error.

Also, don't we need to handle default template template arguments?

template <template <class T> class A, template <class T> class B = A> 
class C;

> +         /* Add this fixed up PARM to the template parms we've fixed
> +            up so far and use that to substitute the fixed-up
> +            template parms into the type of PARM.  */
> +         TREE_VEC_ELT (fixedup_args, i) = template_parm_to_arg (cur);
> +         TREE_TYPE (parm) = tsubst (TREE_TYPE (parm), arglist,
> +                                    tf_none, NULL_TREE);

Don't we need to set the type of pushed_decl, too?

> +         TREE_VALUE (cur) = parm;

But we don't need to set this, as parm hasn't changed.

> +extern void set_template_parms_num_siblings     (tree, int);

I don't think we want this function.  Instead, add a siblings parm to 
build_template_parm_index.

> @@ -17789,7 +18218,8 @@ type_dependent_expression_p (tree expression)
>    if (!processing_template_decl)
>      return false;
>
> -  if (expression == error_mark_node)
> +  if (expression == error_mark_node
> +      || expression == NULL_TREE)

What made this necessary?  I would think this should be caught in the 
caller.

> +  /* If T1 and T2 belong to template parm lists of different size,
> +     let's assume they are different.  */
> +  if (get_template_parms_num_siblings (TYPE_MAIN_VARIANT (t1))
> +      != get_template_parms_num_siblings (TYPE_MAIN_VARIANT (t2)))
>      return false;

> +  /* Then compare their relative position.  */
> +  if (TEMPLATE_TYPE_IDX (t1) != TEMPLATE_TYPE_IDX (t2)
> +      || TEMPLATE_TYPE_LEVEL (t1) != TEMPLATE_TYPE_LEVEL (t2)
> +      || (TEMPLATE_TYPE_PARAMETER_PACK (t1)
> +         != TEMPLATE_TYPE_PARAMETER_PACK (t2)))

All of these are looking at the TEMPLATE_PARM_INDEX, so we might as well 
pull it out and operate on it directly with TEMPLATE_PARM_*.

You need more testcases.

Jason

Patch

diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index b093ce0..1c4e368 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -6671,7 +6671,7 @@  build_self_reference (void)
   DECL_CONTEXT (value) = current_class_type;
   DECL_ARTIFICIAL (value) = 1;
   SET_DECL_SELF_REFERENCE_P (value);
-  cp_set_underlying_type (value);
+  set_underlying_type (value);
 
   if (processing_template_decl)
     value = push_template_decl (value);
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index aa1fe4d..0703a89 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -236,6 +236,7 @@  struct GTY(()) template_parm_index_s {
   int index;
   int level;
   int orig_level;
+  int num_siblings;
   tree decl;
 };
 typedef struct template_parm_index_s template_parm_index;
@@ -4300,6 +4301,9 @@  enum overload_flags { NO_SPECIAL = 0, DTOR_FLAG, TYPENAME_FLAG };
 	((template_parm_index*)TEMPLATE_PARM_INDEX_CHECK (NODE))
 #define TEMPLATE_PARM_IDX(NODE) (TEMPLATE_PARM_INDEX_CAST (NODE)->index)
 #define TEMPLATE_PARM_LEVEL(NODE) (TEMPLATE_PARM_INDEX_CAST (NODE)->level)
+/* The Number of sibling parms this template parm has.  */
+#define TEMPLATE_PARM_NUM_SIBLINGS(NODE) \
+  (TEMPLATE_PARM_INDEX_CAST (NODE)->num_siblings)
 #define TEMPLATE_PARM_DESCENDANTS(NODE) (TREE_CHAIN (NODE))
 #define TEMPLATE_PARM_ORIG_LEVEL(NODE) (TEMPLATE_PARM_INDEX_CAST (NODE)->orig_level)
 #define TEMPLATE_PARM_DECL(NODE) (TEMPLATE_PARM_INDEX_CAST (NODE)->decl)
@@ -4321,10 +4325,6 @@  enum overload_flags { NO_SPECIAL = 0, DTOR_FLAG, TYPENAME_FLAG };
   (TEMPLATE_PARM_DECL (TEMPLATE_TYPE_PARM_INDEX (NODE)))
 #define TEMPLATE_TYPE_PARAMETER_PACK(NODE) \
   (TEMPLATE_PARM_PARAMETER_PACK (TEMPLATE_TYPE_PARM_INDEX (NODE)))
-/* The list of template parms that a given template parameter of type
-   TEMPLATE_TYPE_PARM belongs to.*/
-#define TEMPLATE_TYPE_PARM_SIBLING_PARMS(NODE) \
-  (TREE_CHECK ((NODE), TEMPLATE_TYPE_PARM))->type.maxval
 
 /* These constants can used as bit flags in the process of tree formatting.
 
@@ -5005,7 +5005,7 @@  extern void append_type_to_template_for_access_check (tree, tree, tree,
 extern tree splice_late_return_type		(tree, tree);
 extern bool is_auto				(const_tree);
 extern tree process_template_parm		(tree, location_t, tree, 
-						 bool, bool);
+						 bool, bool, unsigned);
 extern tree end_template_parm_list		(tree);
 extern void end_template_decl			(void);
 extern tree maybe_update_decl_type		(tree, tree);
@@ -5091,6 +5091,8 @@  extern tree get_template_innermost_arguments	(const_tree);
 extern tree get_template_argument_pack_elems	(const_tree);
 extern tree get_function_template_decl		(const_tree);
 extern tree resolve_nondeduced_context		(tree);
+extern int get_template_parms_num_siblings      (tree);
+extern void set_template_parms_num_siblings     (tree, int);
 
 /* in repo.c */
 extern void init_repo				(void);
@@ -5341,7 +5343,6 @@  extern bool type_has_nontrivial_copy_init	(const_tree);
 extern bool class_tmpl_impl_spec_p		(const_tree);
 extern int zero_init_p				(const_tree);
 extern tree strip_typedefs			(tree);
-extern void cp_set_underlying_type		(tree);
 extern tree copy_binfo				(tree, tree, tree,
 						 tree *, int);
 extern int member_p				(const_tree);
diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
index fcc83fb..3ba2a28 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -879,7 +879,7 @@  grokfield (const cp_declarator *declarator,
       if (declspecs->specs[(int)ds_typedef]
           && TREE_TYPE (value) != error_mark_node
           && TYPE_NAME (TYPE_MAIN_VARIANT (TREE_TYPE (value))) != value)
-	cp_set_underlying_type (value);
+	set_underlying_type (value);
 
       return value;
     }
diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index e980cb6..5889adc 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -872,7 +872,7 @@  pushdecl_maybe_friend (tree x, bool is_friend)
 		     inlining.  */
 		  && (!TYPE_NAME (type)
 		      || TYPE_NAME (type) != DECL_ABSTRACT_ORIGIN (x))))
-	    cp_set_underlying_type (x);
+	    set_underlying_type (x);
 
 	  if (type != error_mark_node
 	      && TYPE_NAME (type)
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 82026b1..240d546 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -11011,6 +11011,13 @@  cp_parser_template_parameter_list (cp_parser* parser)
   tree parameter_list = NULL_TREE;
 
   begin_template_parm_list ();
+
+  /* The loop below parses the template parms.  We first need to know
+     the total number of template parms to be able to compute proper
+     canonical types of each dependent type. So after the loop, when
+     we know the total number of template parms,
+     end_template_parm_list computes the proper canonical types and
+     fixes up the dependent types accordingly.  */
   while (true)
     {
       tree parameter;
@@ -11029,11 +11036,11 @@  cp_parser_template_parameter_list (cp_parser* parser)
 						parm_loc,
 						parameter,
 						is_non_type,
-                                                is_parameter_pack);
+						is_parameter_pack,
+						0);
       else
        {
          tree err_parm = build_tree_list (parameter, parameter);
-         TREE_VALUE (err_parm) = error_mark_node;
          parameter_list = chainon (parameter_list, err_parm);
        }
 
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index eabd11b..c6e8798 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -93,10 +93,14 @@  static GTY ((param_is (spec_entry)))
 static GTY ((param_is (spec_entry)))
   htab_t type_specializations;
 
-/* Contains canonical template parameter types. The vector is indexed by
-   the TEMPLATE_TYPE_IDX of the template parameter. Each element is a
-   TREE_LIST, whose TREE_VALUEs contain the canonical template
-   parameters of various types and levels.  */
+/* Contains canonical template parameter types. The vector is indexed
+   by the TEMPLATE_TYPE_IDX of the template parameter. Each element is
+   a TREE_LIST, whose TREE_PURPOSE is a INT_CST tree representing a
+   total size of the template parameter list a given template
+   parameter would belong too, and whose TREE_VALUEs contain the
+   canonical template parameters of various types and levels,
+   belonging to a set of template parameters which size is
+   TREE_PURPOSE.  */
 static GTY(()) VEC(tree,gc) *canonical_template_parms;
 
 #define UNIFY_ALLOW_NONE 0
@@ -190,6 +194,12 @@  static void append_type_to_template_for_access_check_1 (tree, tree, tree,
 static hashval_t iterative_hash_template_arg (tree arg, hashval_t val);
 static tree listify (tree);
 static tree listify_autos (tree, tree);
+static tree template_parm_to_arg (tree t);
+static tree current_template_args (void);
+static tree fixup_template_type_parm_type (tree, int);
+static tree fixup_template_parm_index (tree, tree, int);
+static void fixup_template_parms (void);
+static tree tsubst_template_parm (tree, tree, tsubst_flags_t);
 
 /* Make the current scope suitable for access checking when we are
    processing T.  T can be FUNCTION_DECL for instantiated function
@@ -3369,9 +3379,19 @@  build_template_parm_index (int index,
 
 /* Find the canonical type parameter for the given template type
    parameter.  Returns the canonical type parameter, which may be TYPE
-   if no such parameter existed.  */
+   if no such parameter existed. TOTAL_NUM_PARMS is the number of
+   template parameters carried by the considered template.
+
+   If TYPE is the template parameter at position P in a
+   template, this function won't return the same canonical type as for
+   a another TYPE that would be a template parameter at position Q,
+   with Q != P.
+
+   If TOTAL_NUM_PARMS is 0, it means the number of template parms is
+   not known yet, e.g, we are still parsing the template parms list.  */
+
 static tree
-canonical_type_parameter (tree type)
+canonical_type_parameter (tree type, unsigned total_num_parms)
 {
   tree list;
   int idx = TEMPLATE_TYPE_IDX (type);
@@ -3382,15 +3402,20 @@  canonical_type_parameter (tree type)
     VEC_safe_push (tree, gc, canonical_template_parms, NULL_TREE);
 
   list = VEC_index (tree, canonical_template_parms, idx);
-  while (list && !comptypes (type, TREE_VALUE (list), COMPARE_STRUCTURAL))
-    list = TREE_CHAIN (list);
+  while (list)
+    {
+      if (TREE_INT_CST_LOW (TREE_PURPOSE (list)) == total_num_parms
+	  && comptypes (type, TREE_VALUE (list), COMPARE_STRUCTURAL))
+	break;
+      list = TREE_CHAIN (list);
+    }
 
   if (list)
     return TREE_VALUE (list);
   else
     {
       VEC_replace(tree, canonical_template_parms, idx,
-		  tree_cons (NULL_TREE, type, 
+		  tree_cons (size_int (total_num_parms), type, 
 			     VEC_index (tree, canonical_template_parms, idx)));
       return type;
     }
@@ -3425,6 +3450,7 @@  reduce_template_parm_level (tree index, tree type, int levels, tree args,
 				     TEMPLATE_PARM_ORIG_LEVEL (index),
 				     decl, type);
       TEMPLATE_PARM_DESCENDANTS (index) = t;
+      TEMPLATE_PARM_NUM_SIBLINGS (t) = TEMPLATE_PARM_NUM_SIBLINGS (index);
       TEMPLATE_PARM_PARAMETER_PACK (t) 
 	= TEMPLATE_PARM_PARAMETER_PACK (index);
 
@@ -3438,15 +3464,21 @@  reduce_template_parm_level (tree index, tree type, int levels, tree args,
   return TEMPLATE_PARM_DESCENDANTS (index);
 }
 
-/* Process information from new template parameter PARM and append it to the
-   LIST being built.  This new parameter is a non-type parameter iff
-   IS_NON_TYPE is true. This new parameter is a parameter
-   pack iff IS_PARAMETER_PACK is true.  The location of PARM is in 
-   PARM_LOC.  */
+/* Process information from new template parameter PARM and append it
+   to the LIST being built.  This new parameter is a non-type
+   parameter iff IS_NON_TYPE is true. This new parameter is a
+   parameter pack iff IS_PARAMETER_PACK is true.  The location of PARM
+   is in PARM_LOC. NUM_TEMPLATE_PARMS is the size of the template
+   parameter list PARM belongs to. This is used used to create a
+   proper canonical type for the type of PARM that is to be created,
+   iff PARM is a type.  If the size is not known, this parameter can
+   be set to 0. Setting it to zero would create a template type
+   parameter with no canonical type.  */
 
 tree
-process_template_parm (tree list, location_t parm_loc, tree parm, bool is_non_type, 
-                       bool is_parameter_pack)
+process_template_parm (tree list, location_t parm_loc, tree parm,
+		       bool is_non_type, bool is_parameter_pack,
+		       unsigned num_template_parms)
 {
   tree decl = 0;
   tree defval;
@@ -3556,8 +3588,9 @@  process_template_parm (tree list, location_t parm_loc, tree parm, bool is_non_ty
 				     processing_template_decl,
 				     decl, TREE_TYPE (parm));
       TEMPLATE_TYPE_PARAMETER_PACK (t) = is_parameter_pack;
-      TYPE_CANONICAL (t) = canonical_type_parameter (t);
-    }
+      TYPE_CANONICAL (t) =
+	canonical_type_parameter (t, num_template_parms);
+   }
   DECL_ARTIFICIAL (decl) = 1;
   SET_DECL_TEMPLATE_PARM_P (decl);
   pushdecl (decl);
@@ -3573,9 +3606,9 @@  process_template_parm (tree list, location_t parm_loc, tree parm, bool is_non_ty
 tree
 end_template_parm_list (tree parms)
 {
-  int nparms;
+  int nparms, length = list_length (parms);
   tree parm, next;
-  tree saved_parmlist = make_tree_vec (list_length (parms));
+  tree saved_parmlist = make_tree_vec (length);
 
   current_template_parms
     = tree_cons (size_int (processing_template_decl),
@@ -3586,16 +3619,305 @@  end_template_parm_list (tree parms)
       next = TREE_CHAIN (parm);
       TREE_VEC_ELT (saved_parmlist, nparms) = parm;
       TREE_CHAIN (parm) = NULL_TREE;
-      if (TREE_CODE (TREE_VALUE (parm)) == TYPE_DECL)
-	TEMPLATE_TYPE_PARM_SIBLING_PARMS (TREE_TYPE (TREE_VALUE (parm))) =
-	      current_template_parms;
     }
 
+  fixup_template_parms ();
+
   --processing_template_parmlist;
 
   return saved_parmlist;
 }
 
+/* Create a new type almost identical to TYPE but which has the
+   following differences:
+
+     1/ T has a new TEMPLATE_PARM_INDEX that carries the new number of
+     template sibling parameters of T.
+
+     2/ T has a new canonical type that matches the new number
+     of sibling parms.
+
+     3/ From now on, T is going to be what lookups referring to the
+     name of TYPE will return. No lookup should return TYPE anymore.
+
+   NUM_PARMS is the new number of sibling parms TYPE belongs to.
+
+   This is a subroutine of fixup_template_parms.  */
+
+static tree
+fixup_template_type_parm_type (tree type, int num_parms)
+{
+  tree orig_idx = TEMPLATE_TYPE_PARM_INDEX (type), idx;
+  tree t = copy_type (type);
+  /* This is the decl which name is inserted into the symbol table for
+     the template parm type. So whenever we lookup the type name, this
+     is the DECL we get.  */
+  tree decl = TYPE_NAME (t);
+
+  TYPE_MAIN_VARIANT (t) = t;
+  TYPE_NEXT_VARIANT (t)= NULL_TREE;
+  TYPE_POINTER_TO (t) = 0;
+  TYPE_REFERENCE_TO (t) = 0;
+
+  idx = build_template_parm_index (TEMPLATE_PARM_IDX (orig_idx),
+				   TEMPLATE_PARM_LEVEL (orig_idx),
+				   TEMPLATE_PARM_ORIG_LEVEL (orig_idx),
+				   decl, t);
+  TEMPLATE_PARM_DESCENDANTS (idx) = TEMPLATE_PARM_DESCENDANTS (orig_idx);
+  TEMPLATE_PARM_PARAMETER_PACK (idx) = TEMPLATE_PARM_PARAMETER_PACK (orig_idx);
+  set_template_parms_num_siblings (idx, num_parms);
+  TEMPLATE_TYPE_PARM_INDEX (t) = idx;
+
+  TYPE_STUB_DECL (t) = decl;
+  TEMPLATE_TYPE_DECL (t) = decl;
+  if (TREE_CODE (type) == TEMPLATE_TEMPLATE_PARM)
+    TREE_TYPE (DECL_TEMPLATE_RESULT  (decl)) = t;
+
+  /* Update the type associated to the type name stored in the symbol
+     table. Now, whenever the type name is looked up, the resulting
+     type is properly fixed up.  */
+  TREE_TYPE (decl) = t;
+
+  TYPE_CANONICAL (t) = canonical_type_parameter (t, num_parms);
+
+  return t;
+}
+
+/* Create and return a new TEMPLATE_PARM_INDEX that is almost
+   identical to I, but that is fixed up as to:
+
+   1/ carry the number of sibling parms (NUM_PARMS) of the template
+   parm represented by I.
+
+   2/ replace all references to template parm types declared before I
+   (in the same template parm list as I) by references to template
+   parm types contained in ARGS. ARGS should contain the list of
+   template parms that have been fixed up so far, in a form suitable
+   to be passed to tsubst.
+
+   This is a subroutine of fixup_template_parms.  */
+
+static tree
+fixup_template_parm_index (tree i, tree args, int num_parms)
+{
+  tree index, decl, type;
+
+  if (i == NULL_TREE
+      || TREE_CODE (i) != TEMPLATE_PARM_INDEX)
+    return i;
+
+  decl = TEMPLATE_PARM_DECL (i);
+  type = TREE_TYPE (decl);
+
+  index = build_template_parm_index (TEMPLATE_PARM_IDX (i),
+				     TEMPLATE_PARM_LEVEL (i),
+				     TEMPLATE_PARM_ORIG_LEVEL (i),
+				     decl, type);
+
+  TEMPLATE_PARM_DESCENDANTS (index) = TEMPLATE_PARM_DESCENDANTS (i);
+  TEMPLATE_PARM_PARAMETER_PACK (index) = TEMPLATE_PARM_PARAMETER_PACK (i);
+  set_template_parms_num_siblings (index, num_parms);
+
+  type = tsubst (type, args, tf_none, NULL_TREE);
+  
+  TREE_TYPE (decl) = type;
+  TREE_TYPE (index) = type;
+
+  return index;
+}
+
+/* Walk current the template parms and properly compute the canonical
+   types of the dependent types created during
+   cp_parser_template_parameter_list.  */
+
+static void
+fixup_template_parms (void)
+{
+  tree parm;
+  tree arglist;
+  tree parameter_vec;
+  tree fixedup_args;
+  int i, num_parms;
+
+  parameter_vec = INNERMOST_TEMPLATE_PARMS (current_template_parms);
+  if (parameter_vec == NULL_TREE)
+    return;
+
+  num_parms = TREE_VEC_LENGTH (parameter_vec);
+
+  /* This vector contains the current innermost template parms that
+     have been fixed up so far.  The form of FIXEDUP_ARGS is suitable
+     to be passed to tsubst* functions as their ARGS argument.  */
+  fixedup_args = make_tree_vec (num_parms);
+
+  /* This vector contains the full set of template parms in a form
+     suitable to be passed to substs functions as their ARGS
+     argument.  */
+  arglist = current_template_args ();
+  arglist = add_outermost_template_args (arglist, fixedup_args);
+
+  fixedup_args = INNERMOST_TEMPLATE_ARGS (arglist);
+
+  /* Let's do the proper fixup now.  */
+  for (i = 0; i < num_parms; ++i)
+    {
+      tree cur = TREE_VEC_ELT (parameter_vec, i);
+
+      /* This is the current template parameter we need to fix up.  */
+      parm = TREE_VALUE (cur);
+
+      if (TREE_CODE (parm) == TYPE_DECL)
+	{
+	  /* PARM is a template type parameter. Fix up its type, add
+	     the fixed-up template parm to the vector of fixed-up
+	     template parms so far, and substitute the fixed-up
+	     template parms into the default argument of this
+	     parameter.  */
+
+	  tree t =
+	    fixup_template_type_parm_type (TREE_TYPE (parm), num_parms);
+	  TREE_TYPE (parm) = t;
+
+	  TREE_VEC_ELT (fixedup_args, i) = template_parm_to_arg (cur);
+
+	  if (TREE_PURPOSE (cur))
+	    {
+	      /* So the current template type parameter has a default
+		 argument. Substitute the so far fixed-up template
+		 parms into it.   */
+	      tree default_arg = TREE_PURPOSE (cur);
+
+	      if (TYPE_P (default_arg)
+		  && !dependent_type_p (default_arg))
+		continue;
+
+	      arglist = current_template_args ();
+	      ++cp_unevaluated_operand;
+	      TREE_PURPOSE (cur) =
+		tsubst_expr (default_arg, arglist,
+			     tf_none, default_arg, false);
+	      --cp_unevaluated_operand;
+	    }
+	}
+      else if (TREE_CODE (parm) == TEMPLATE_DECL)
+	{
+	  /* PARM is a template template parameter. This is going to
+	     be interesting.  */
+	  tree tparms, targs, innermost_args;
+	  int j;
+
+	  /* First, fix up the type of the parm.  */
+
+	  tree t =
+	    fixup_template_type_parm_type (TREE_TYPE (parm), num_parms);
+	  TREE_TYPE (parm) = t;
+
+	  TREE_VEC_ELT (fixedup_args, i) = template_parm_to_arg (cur);
+
+	  /* Now we need to substitute the template parm types that
+	     have been fixed up so far into the non-type template
+	     parms of this template template parm. E.g, consider this:
+
+	     template<class T, template<T u> class TT> class S;
+
+	     In this case we want to substitute T into the
+	     template parameters of TT.
+
+	     Sot let's walk the template parms of PARM here, and
+	     tsubst ARGLIST into into each of the template
+	     parms.   */
+
+	  /* For this substitution we need to build the full set of
+	     template parameters and use that as arguments for the
+	     tsubsting function.  */
+	  tparms = INNERMOST_TEMPLATE_PARMS (DECL_TEMPLATE_PARMS (parm));
+
+	  /* This will contain the innermost parms of PARM into which
+	     we have substituted so far.  */
+	  innermost_args = make_tree_vec (TREE_VEC_LENGTH (tparms));
+	  targs = add_to_template_args (arglist, innermost_args);
+	  for (j = 0; j < TREE_VEC_LENGTH (tparms); ++j)
+	    {
+	      tree substed_parm, parameter;
+
+	      parameter = TREE_VEC_ELT (tparms, j);
+
+	      /* INNERMOST_ARGS needs to have at least the same number
+		 of elements as the index PARAMETER, ortherwise
+		 tsubsting into PARAMETER will result in partially
+		 instantiating it, reducing its tempate parm
+		 level. Let's tactically fill INNERMOST_ARGS for that
+		 purpose.  */
+	      TREE_VEC_ELT (innermost_args, j) = template_parm_to_arg (parameter);
+
+	      /* Only substitute into template non-type parms.  */
+	      if (parameter != NULL_TREE
+		  && TREE_CODE (parameter) == TREE_LIST
+		  && (TREE_CODE (TREE_VALUE (parameter)) == TYPE_DECL
+		      || TREE_CODE (TREE_VALUE (parameter)) == TEMPLATE_DECL))
+		continue;
+
+	      if (!dependent_type_p (TREE_TYPE (TREE_VALUE (parameter))))
+		continue;
+
+	      ++cp_unevaluated_operand;
+	      substed_parm = tsubst_template_parm (parameter, targs, tf_none);
+	      --cp_unevaluated_operand;
+
+	      /* Update the template parameters of PARM.  */
+	      TREE_VEC_ELT (tparms, j) = substed_parm;
+
+	      /* Update the vector of parms we have tsubsted into so
+		 far.  */
+	      TREE_VEC_ELT (innermost_args, j) =
+		template_parm_to_arg (substed_parm);
+	    }
+	}
+      else if (TREE_CODE (parm) == PARM_DECL)
+	{
+	  /* PARM is a non-type template parameter. We need to:
+
+	   * Fix up its TEMPLATE_PARM_INDEX to make it carry the
+	     proper number of sibling parameters.
+
+	   * Make lookups of the template parameter return a reference
+	     to the fixed-up index. No lookup should return references
+	     to the former index anymore.
+
+	   * Substitute the template parms that got fixed up so far
+
+	   * into the type of PARM.  */
+
+	  tree index = DECL_INITIAL (parm);
+
+	  /* PUSHED_DECL is the decl added to the symbol table with
+	     the name of the parameter. E,g:
+	     
+	     template<class T, T u> //#0
+	     auto my_function(T t) -> decltype(u); //#1
+
+	    Here, when looking up u at //#1, we get the decl of u
+	    resulting from the declaration in #0. This is what
+	    PUSHED_DECL is. We need to replace the reference to the
+	    old TEMPLATE_PARM_INDEX carried by PUSHED_DECL by the
+	    fixed-up TEMPLATE_PARM_INDEX.  */
+	  tree pushed_decl = TEMPLATE_PARM_DECL (index);
+	  tree fixed_up_index =
+	    fixup_template_parm_index (index, arglist, num_parms);
+
+	  DECL_INITIAL (pushed_decl) = DECL_INITIAL (parm) = fixed_up_index;
+
+	  /* Add this fixed up PARM to the template parms we've fixed
+	     up so far and use that to substitute the fixed-up
+	     template parms into the type of PARM.  */
+	  TREE_VEC_ELT (fixedup_args, i) = template_parm_to_arg (cur);
+	  TREE_TYPE (parm) = tsubst (TREE_TYPE (parm), arglist,
+				     tf_none, NULL_TREE);
+	  TREE_VALUE (cur) = parm;
+	}
+    }
+}
+
 /* end_template_decl is called after a template declaration is seen.  */
 
 void
@@ -3613,6 +3935,65 @@  end_template_decl (void)
   current_template_parms = TREE_CHAIN (current_template_parms);
 }
 
+/* Takes a TREE_LIST representing a template parameter and convert it
+   into an argument suitable to be passed to the type substitution
+   functions.  */
+
+static tree
+template_parm_to_arg (tree t)
+{
+
+  if (t == NULL_TREE
+      || TREE_CODE (t) != TREE_LIST
+      || error_operand_p (TREE_VALUE (t)))
+    return t;
+
+  t = TREE_VALUE (t);
+
+  if (TREE_CODE (t) == TYPE_DECL
+      || TREE_CODE (t) == TEMPLATE_DECL)
+    {
+      t = TREE_TYPE (t);
+
+      if (TEMPLATE_TYPE_PARAMETER_PACK (t))
+	{
+	  /* Turn this argument into a TYPE_ARGUMENT_PACK
+	     with a single element, which expands T.  */
+	  tree vec = make_tree_vec (1);
+#ifdef ENABLE_CHECKING
+	  SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT
+	    (vec, TREE_VEC_LENGTH (vec));
+#endif
+	  TREE_VEC_ELT (vec, 0) = make_pack_expansion (t);
+
+	  t = cxx_make_type (TYPE_ARGUMENT_PACK);
+	  SET_ARGUMENT_PACK_ARGS (t, vec);
+	}
+    }
+  else
+    {
+      t = DECL_INITIAL (t);
+
+      if (TEMPLATE_PARM_PARAMETER_PACK (t))
+	{
+	  /* Turn this argument into a NONTYPE_ARGUMENT_PACK
+	     with a single element, which expands T.  */
+	  tree vec = make_tree_vec (1);
+	  tree type = TREE_TYPE (TEMPLATE_PARM_DECL (t));
+#ifdef ENABLE_CHECKING
+	  SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT
+	    (vec, TREE_VEC_LENGTH (vec));
+#endif
+	  TREE_VEC_ELT (vec, 0) = make_pack_expansion (t);
+
+	  t  = make_node (NONTYPE_ARGUMENT_PACK);
+	  SET_ARGUMENT_PACK_ARGS (t, vec);
+	  TREE_TYPE (t) = type;
+	}
+    }
+  return t;
+}
+
 /* Within the declaration of a template, return all levels of template
    parameters that apply.  The template parameters are represented as
    a TREE_VEC, in the form documented in cp-tree.h for template
@@ -3639,63 +4020,7 @@  current_template_args (void)
 
       TREE_TYPE (a) = NULL_TREE;
       for (i = TREE_VEC_LENGTH (a) - 1; i >= 0; --i)
-	{
-	  tree t = TREE_VEC_ELT (a, i);
-
-	  /* T will be a list if we are called from within a
-	     begin/end_template_parm_list pair, but a vector directly
-	     if within a begin/end_member_template_processing pair.  */
-	  if (TREE_CODE (t) == TREE_LIST)
-	    {
-	      t = TREE_VALUE (t);
-
-	      if (!error_operand_p (t))
-		{
-		  if (TREE_CODE (t) == TYPE_DECL
-		      || TREE_CODE (t) == TEMPLATE_DECL)
-                    {
-                      t = TREE_TYPE (t);
-                      
-                      if (TEMPLATE_TYPE_PARAMETER_PACK (t))
-                        {
-                          /* Turn this argument into a TYPE_ARGUMENT_PACK
-                             with a single element, which expands T.  */
-                          tree vec = make_tree_vec (1);
-#ifdef ENABLE_CHECKING
-			  SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT
-				(vec, TREE_VEC_LENGTH (vec));
-#endif
-                          TREE_VEC_ELT (vec, 0) = make_pack_expansion (t);
-                          
-                          t = cxx_make_type (TYPE_ARGUMENT_PACK);
-                          SET_ARGUMENT_PACK_ARGS (t, vec);
-                        }
-                    }
-                  else
-                    {
-                      t = DECL_INITIAL (t);
-                      
-                      if (TEMPLATE_PARM_PARAMETER_PACK (t))
-                        {
-                          /* Turn this argument into a NONTYPE_ARGUMENT_PACK
-                             with a single element, which expands T.  */
-                          tree vec = make_tree_vec (1);
-                          tree type = TREE_TYPE (TEMPLATE_PARM_DECL (t));
-#ifdef ENABLE_CHECKING
-			  SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT
-				(vec, TREE_VEC_LENGTH (vec));
-#endif
-                          TREE_VEC_ELT (vec, 0) = make_pack_expansion (t);
-                          
-                          t  = make_node (NONTYPE_ARGUMENT_PACK);
-                          SET_ARGUMENT_PACK_ARGS (t, vec);
-                          TREE_TYPE (t) = type;
-                        }
-                    }
-		  TREE_VEC_ELT (a, i) = t;
-                }
-	    }
-	}
+	TREE_VEC_ELT (a, i) = template_parm_to_arg (TREE_VEC_ELT (a, i));
 
 #ifdef ENABLE_CHECKING
       SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (a, TREE_VEC_LENGTH (a));
@@ -3706,7 +4031,23 @@  current_template_args (void)
       else
 	args = a;
     }
-
+  
+    if (length > 1 && TREE_VEC_ELT (args, 0) == NULL_TREE)
+      /* This can happen for template parms of a template template
+	 parameter, e.g:
+
+	 template<template<class T, class U> class TT> struct S;
+
+	 Consider the level of the parms of TT; T and U both have
+	 level 2; TT has no template parm of level 1. So in this case
+	 the first element of full_template_args is NULL_TREE. If we
+	 leave it like this TMPL_ARG_DEPTH on args returns 1 instead
+	 of 2. This will make tsubst wrongly consider that T and U
+	 have level 1. Instead, let's create a dummy vector as the
+	 first element of full_template_args so that TMPL_ARG_DEPTH
+	 returns the correct depth for args.
+      */
+      TREE_VEC_ELT (args, 0) = make_tree_vec (1);
   return args;
 }
 
@@ -8740,8 +9081,6 @@  tsubst_template_parms (tree parms, tree args, tsubst_flags_t complain)
       for (i = 0; i < TREE_VEC_LENGTH (new_vec); ++i)
 	{
           tree tuple;
-          tree default_value;
-          tree parm_decl;
 
           if (parms == error_mark_node)
             continue;
@@ -8751,18 +9090,8 @@  tsubst_template_parms (tree parms, tree args, tsubst_flags_t complain)
           if (tuple == error_mark_node)
             continue;
 
-          default_value = TREE_PURPOSE (tuple);
-          parm_decl = TREE_VALUE (tuple);
-
-	  parm_decl = tsubst (parm_decl, args, complain, NULL_TREE);
-	  if (TREE_CODE (parm_decl) == PARM_DECL
-	      && invalid_nontype_parm_type_p (TREE_TYPE (parm_decl), complain))
-	    parm_decl = error_mark_node;
-	  default_value = tsubst_template_arg (default_value, args,
-					       complain, NULL_TREE);
-
-	  tuple = build_tree_list (default_value, parm_decl);
-	  TREE_VEC_ELT (new_vec, i) = tuple;
+	  TREE_VEC_ELT (new_vec, i) =
+	    tsubst_template_parm (tuple, args, complain);
 	}
 
       *new_parms =
@@ -8776,6 +9105,100 @@  tsubst_template_parms (tree parms, tree args, tsubst_flags_t complain)
   return r;
 }
 
+/* Return the result of substituting ARGS into one template parameter
+   given by T. T Must be a TREE_LIST which TREE_VALUE is the template
+   parameter and which TREE_PURPOSE is the default argument of the
+   template parameter.  */
+
+static tree
+tsubst_template_parm (tree t, tree args, tsubst_flags_t complain)
+{
+  tree default_value, parm_decl;
+
+  if (args == NULL_TREE
+      || t == NULL_TREE
+      || t == error_mark_node)
+    return t;
+
+  gcc_assert (TREE_CODE (t) == TREE_LIST);
+
+  default_value = TREE_PURPOSE (t);
+  parm_decl = TREE_VALUE (t);
+
+  parm_decl = tsubst (parm_decl, args, complain, NULL_TREE);
+  if (TREE_CODE (parm_decl) == PARM_DECL
+      && invalid_nontype_parm_type_p (TREE_TYPE (parm_decl), complain))
+    parm_decl = error_mark_node;
+  default_value = tsubst_template_arg (default_value, args,
+				       complain, NULL_TREE);
+
+  return build_tree_list (default_value, parm_decl);
+}
+
+/* Return the size of template of the parameters list T belongs to.  T
+   is either a template parameter type, a template non-type parameter
+   or a template parameter index.  */
+
+int
+get_template_parms_num_siblings (tree t)
+{
+  unsigned result;
+
+  gcc_assert (t != NULL_TREE
+	      && (TREE_CODE (t) == TEMPLATE_PARM_INDEX
+		  || TREE_CODE (t) == TEMPLATE_TYPE_PARM
+		  || TREE_CODE (t) == TEMPLATE_TEMPLATE_PARM
+		  || TREE_CODE (t) == BOUND_TEMPLATE_TEMPLATE_PARM
+		  || (TREE_CODE (t) == PARM_DECL
+		      && DECL_TEMPLATE_PARM_P (t))));
+
+  switch (TREE_CODE (t))
+    {
+    case TEMPLATE_PARM_INDEX:
+      result = TEMPLATE_PARM_NUM_SIBLINGS (t);
+      break;
+    case PARM_DECL:
+      result = get_template_parms_num_siblings (DECL_INITIAL (t));
+      break;
+    default:
+      result =
+	get_template_parms_num_siblings (TEMPLATE_TYPE_PARM_INDEX (t));
+      break;
+    }
+  return result;
+}
+
+/* Set the size of template of the parameters list T belongs to.  T is
+   either a template parameter type, a template non-type parameter or
+   a template parameter index.  */
+
+void
+set_template_parms_num_siblings (tree t, int num_parms)
+{
+  gcc_assert (t != NULL_TREE
+	      && (TREE_CODE (t) == TEMPLATE_PARM_INDEX
+		  || TREE_CODE (t) == TEMPLATE_TYPE_PARM
+		  || TREE_CODE (t) == TEMPLATE_TEMPLATE_PARM
+		  || TREE_CODE (t) == BOUND_TEMPLATE_TEMPLATE_PARM
+		  || (TREE_CODE (t) == PARM_DECL
+		      && DECL_TEMPLATE_PARM_P (t))));
+
+  switch (TREE_CODE (t))
+    {
+    case TEMPLATE_PARM_INDEX:
+      TEMPLATE_PARM_NUM_SIBLINGS (t) = num_parms;
+      break;
+    case PARM_DECL:
+      set_template_parms_num_siblings (DECL_INITIAL (t), num_parms);
+      break;
+    default:
+      set_template_parms_num_siblings (TEMPLATE_TYPE_PARM_INDEX (t),
+				       num_parms);
+      break;
+    }
+}
+
+
 /* Substitute the ARGS into the indicated aggregate (or enumeration)
    type T.  If T is not an aggregate or enumeration type, it is
    handled as if by tsubst.  IN_DECL is as for tsubst.  If
@@ -10291,7 +10714,12 @@  tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 		else if (TYPE_STRUCTURAL_EQUALITY_P (t))
 		  SET_TYPE_STRUCTURAL_EQUALITY (r);
 		else
-		  TYPE_CANONICAL (r) = canonical_type_parameter (r);
+		  {
+		    int num_parms =
+		      get_template_parms_num_siblings (t);
+		    TYPE_CANONICAL (r) =
+		      canonical_type_parameter (r, num_parms);
+		  }
 
 		if (code == BOUND_TEMPLATE_TEMPLATE_PARM)
 		  {
@@ -14701,6 +15129,7 @@  unify (tree tparms, tree targs, tree parm, tree arg, int strict)
 	  {
 	    tree parmvec = TYPE_TI_ARGS (parm);
 	    tree argvec = INNERMOST_TEMPLATE_ARGS (TYPE_TI_ARGS (arg));
+	    tree full_argvec = add_to_template_args (targs, argvec);
 	    tree parm_parms 
               = DECL_INNERMOST_TEMPLATE_PARMS
 	          (TEMPLATE_TEMPLATE_PARM_TEMPLATE_DECL (parm));
@@ -14735,7 +15164,7 @@  unify (tree tparms, tree targs, tree parm, tree arg, int strict)
 	      the global operator+ will be used; if they are not, the
 	      Lvalue_proxy will be converted to float.  */
 	    if (coerce_template_parms (parm_parms,
-                                       argvec,
+                                       full_argvec,
 				       TYPE_TI_TEMPLATE (parm),
 				       tf_none,
 				       /*require_all_args=*/true,
@@ -17781,7 +18210,8 @@  type_dependent_expression_p (tree expression)
   if (!processing_template_decl)
     return false;
 
-  if (expression == error_mark_node)
+  if (expression == error_mark_node
+      || expression == NULL_TREE)
     return false;
 
   /* An unresolved name is always dependent.  */
@@ -18401,7 +18831,7 @@  make_auto (void)
   TEMPLATE_TYPE_PARM_INDEX (au) = build_template_parm_index
     (0, processing_template_decl + 1, processing_template_decl + 1,
      TYPE_NAME (au), NULL_TREE);
-  TYPE_CANONICAL (au) = canonical_type_parameter (au);
+  TYPE_CANONICAL (au) = canonical_type_parameter (au, 0);
   DECL_ARTIFICIAL (TYPE_NAME (au)) = 1;
   SET_DECL_TEMPLATE_PARM_P (TYPE_NAME (au));
 
diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index ddfb354..f238f5a 100644
--- a/gcc/cp/tree.c
+++ b/gcc/cp/tree.c
@@ -1062,22 +1062,6 @@  strip_typedefs (tree t)
   return cp_build_qualified_type (result, cp_type_quals (t));
 }
 
-/* Setup a TYPE_DECL node as a typedef representation.
-   See comments of set_underlying_type in c-common.c.  */
-
-void
-cp_set_underlying_type (tree t)
-{
-  set_underlying_type (t);
-  /* If T is a template type parm, make it require structural equality.
-     This is useful when comparing two template type parms,
-     because it forces the comparison of the template parameters of their
-     decls.  */
-  if (TREE_CODE (TREE_TYPE (t)) == TEMPLATE_TYPE_PARM)
-    SET_TYPE_STRUCTURAL_EQUALITY (TREE_TYPE (t));
-}
-
-
 /* Makes a copy of BINFO and TYPE, which is to be inherited into a
    graph dominated by T.  If BINFO is NULL, TYPE is a dependent base,
    and we do a shallow copy.  If BINFO is non-NULL, we do a deep copy.
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index eff6704..13d1ae1 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -1143,114 +1143,20 @@  comp_template_parms_position (tree t1, tree t2)
 		  || TREE_CODE (t1) == TEMPLATE_TEMPLATE_PARM
 		  || TREE_CODE (t1) == TEMPLATE_TYPE_PARM));
 
-      if (TEMPLATE_TYPE_IDX (t1) != TEMPLATE_TYPE_IDX (t2)
-	  || TEMPLATE_TYPE_LEVEL (t1) != TEMPLATE_TYPE_LEVEL (t2)
-          || (TEMPLATE_TYPE_PARAMETER_PACK (t1) 
-              != TEMPLATE_TYPE_PARAMETER_PACK (t2)))
-	return false;
-
-      return true;
-}
-
-/* Subroutine of incompatible_dependent_types_p.
-   Return the template parameter of the dependent type T.
-   If T is a typedef, return the template parameters of
-   the _decl_ of the typedef. T must be a dependent type.  */
-
-static tree
-get_template_parms_of_dependent_type (tree t)
-{
-  tree tinfo = NULL_TREE, tparms = NULL_TREE;
-
-  /* First, try the obvious case of getting the
-     template info from T itself.  */
-  if ((tinfo = get_template_info (t)))
-    ;
-  else if (TREE_CODE (t) == TEMPLATE_TYPE_PARM)
-    return TEMPLATE_TYPE_PARM_SIBLING_PARMS (t);
-  else if (typedef_variant_p (t)
-	   && !NAMESPACE_SCOPE_P (TYPE_NAME (t)))
-    tinfo = get_template_info (DECL_CONTEXT (TYPE_NAME (t)));
-  /* If T is a TYPENAME_TYPE which context is a template type
-     parameter, get the template parameters from that context.  */
-  else if (TYPE_CONTEXT (t)
-	   && TREE_CODE (TYPE_CONTEXT (t)) == TEMPLATE_TYPE_PARM)
-   return TEMPLATE_TYPE_PARM_SIBLING_PARMS (TYPE_CONTEXT (t));
-  else if (TYPE_CONTEXT (t)
-	   && !NAMESPACE_SCOPE_P (t))
-    tinfo = get_template_info (TYPE_CONTEXT (t));
-
-  if (tinfo)
-    tparms = DECL_TEMPLATE_PARMS (TI_TEMPLATE (tinfo));
-
-  return tparms;
-}
-
-/* Subroutine of structural_comptypes.
-   Compare the dependent types T1 and T2.
-   Return TRUE if we are sure they can't be equal, FALSE otherwise.
-   The whole point of this function is to support cases where either T1 or
-   T2 is a typedef. In those cases, we need to compare the template parameters
-   of the _decl_ of the typedef. If those don't match then we know T1
-   and T2 cannot be equal.  */
-
-static bool
-incompatible_dependent_types_p (tree t1, tree t2)
-{
-  tree tparms1 = NULL_TREE, tparms2 = NULL_TREE;
-  bool t1_typedef_variant_p, t2_typedef_variant_p;
-
-  if (!uses_template_parms (t1) || !uses_template_parms (t2))
-    return false;
-
-  if (TREE_CODE (t1) == TEMPLATE_TYPE_PARM)
-    {
-      /* If T1 and T2 don't have the same relative position in their
-	 template parameters set, they can't be equal.  */
-      if (!comp_template_parms_position (t1, t2))
-	return true;
-    }
-
-  t1_typedef_variant_p = typedef_variant_p (t1);
-  t2_typedef_variant_p = typedef_variant_p (t2);
-
-  /* Either T1 or T2 must be a typedef.  */
-  if (!t1_typedef_variant_p && !t2_typedef_variant_p)
+  /* If T1 and T2 belong to template parm lists of different size,
+     let's assume they are different.  */
+  if (get_template_parms_num_siblings (TYPE_MAIN_VARIANT (t1))
+      != get_template_parms_num_siblings (TYPE_MAIN_VARIANT (t2)))
     return false;
 
-  if (!t1_typedef_variant_p || !t2_typedef_variant_p)
-    /* Either T1 or T2 is not a typedef so we cannot compare the
-       template parms of the typedefs of T1 and T2.
-       At this point, if the main variant type of T1 and T2 are equal
-       it means the two types can't be incompatible, from the perspective
-       of this function.  */
-    if (TYPE_MAIN_VARIANT (t1) == TYPE_MAIN_VARIANT (t2))
-      return false;
-
-  /* So if we reach this point, it means either T1 or T2 is a typedef variant.
-     Let's compare their template parameters.  */
-
-  tparms1 = get_template_parms_of_dependent_type (t1);
-  tparms2 = get_template_parms_of_dependent_type (t2);
-
-  /* If T2 is a template type parm and if we could not get the template
-     parms it belongs to, that means we have not finished parsing the
-     full set of template parameters of the template declaration it
-     belongs to yet. If we could get the template parms T1 belongs to,
-     that mostly means T1 and T2 belongs to templates that are
-     different and incompatible.  */
-  if (TREE_CODE (t1) == TEMPLATE_TYPE_PARM
-      && (tparms1 == NULL_TREE || tparms2 == NULL_TREE)
-      && tparms1 != tparms2)
-    return true;
-
-  if (tparms1 == NULL_TREE
-      || tparms2 == NULL_TREE
-      || tparms1 == tparms2)
+  /* Then compare their relative position.  */
+  if (TEMPLATE_TYPE_IDX (t1) != TEMPLATE_TYPE_IDX (t2)
+      || TEMPLATE_TYPE_LEVEL (t1) != TEMPLATE_TYPE_LEVEL (t2)
+      || (TEMPLATE_TYPE_PARAMETER_PACK (t1) 
+	  != TEMPLATE_TYPE_PARAMETER_PACK (t2)))
     return false;
 
-  /* And now compare the mighty template parms!  */
-  return !comp_template_parms (tparms1, tparms2);
+  return true;
 }
 
 /* Subroutine in comptypes.  */
@@ -1295,12 +1201,6 @@  structural_comptypes (tree t1, tree t2, int strict)
   if (TYPE_FOR_JAVA (t1) != TYPE_FOR_JAVA (t2))
     return false;
 
-  /* If T1 and T2 are dependent typedefs then check upfront that
-     the template parameters of their typedef DECLs match before
-     going down checking their subtypes.  */
-  if (incompatible_dependent_types_p (t1, t2))
-    return false;
-
   /* Allow for two different type nodes which have essentially the same
      definition.  Note that we already checked for equality of the type
      qualifiers (just above).  */
@@ -1345,6 +1245,7 @@  structural_comptypes (tree t1, tree t2, int strict)
 	  (DECL_TEMPLATE_PARMS (TEMPLATE_TEMPLATE_PARM_TEMPLATE_DECL (t1)),
 	   DECL_TEMPLATE_PARMS (TEMPLATE_TEMPLATE_PARM_TEMPLATE_DECL (t2))))
 	return false;
+
       if (TREE_CODE (t1) == TEMPLATE_TEMPLATE_PARM)
 	break;
       /* Don't check inheritance.  */
@@ -1401,8 +1302,10 @@  structural_comptypes (tree t1, tree t2, int strict)
       break;
 
     case TEMPLATE_TYPE_PARM:
-      /* If incompatible_dependent_types_p called earlier didn't decide
-         T1 and T2 were different, they might be equal.  */
+      /* If T1 and T2 don't have the same relative position in their
+	 template parameters set, they can't be equal.  */
+      if (!comp_template_parms_position (t1, t2))
+	return false;
       break;
 
     case TYPENAME_TYPE:
diff --git a/gcc/testsuite/g++.dg/template/typedef36.C b/gcc/testsuite/g++.dg/template/typedef36.C
new file mode 100644
index 0000000..f6155c1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/typedef36.C
@@ -0,0 +1,23 @@ 
+// Origin: PR c++/45606
+// { dg-do compile }
+
+#include <list>
+
+template<class T>
+class Test
+{
+protected:
+  typedef std::list<T> ListAlias;
+  ListAlias list;
+public:
+  typedef typename ListAlias::const_iterator const_iterator;
+  inline const_iterator begin() const;
+
+};
+
+template<class T>
+inline typename std::list<T>::const_iterator Test<T>::begin() const
+{
+  return list.begin();
+}
+