Patchwork Require canonical type comparison for typedefs again.

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Submitter Dodji Seketeli
Date Oct. 15, 2010, 3:44 p.m.
Message ID <m3wrpjfokl.fsf@seketeli.org>
Download mbox | patch
Permalink /patch/67978/
State New
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Comments

Dodji Seketeli - Oct. 15, 2010, 3:44 p.m.
Hello Paolo, Jason,

I am replying to both of your messages in below.

Paolo Carlini <pcarlini@gmail.com> writes:

[...]

>> 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>

[...]

>
> 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.

You are right. Sorry for not having done it before. It is now done in
the udpated patch below.


Jason Merrill <jason@redhat.com> writes:

[...]

>> -/* 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.

Done.

>
>> +         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?
>

I wonder why myself. Thanks for catching this. I removed it.

>> +             ++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.
>

Done.

>> +         /* 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;

Oops, done now.

>> +             ++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.

Done.

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

I am not sure about this but can a default template template argument
depend on the template parms of the current template being declared?
e.g, in:

template<class T>
struct C
{
};

template<class U,
	 template<class V> class W = C>
struct S
{
};

Here, the template parms of C haven't been created in the template parm
list of S. Furthermore, couldn't tsubsting U into C would wrongly
remplace the template parm T of C with U? I said wrongly because now
with this patch T and U are different types.

> 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?

Ah, it is done by the call to fixup_template_parm_index right before the
snippet of code you quoted. as that function takes care of updating all
references to template type parms from the index. I have added a comment
for that.

>
>> +         TREE_VALUE (cur) = parm;
>
> But we don't need to set this, as parm hasn't changed.
>

Sigh. True. Removed.

>> +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.
>

Done.

>> @@ -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.

This is actually not necessary. I think I tentatively added this while
looking for why I was breaking so many regression tests at some point
and forgot to remove it. I have removed it from the patch.

>
>> +  /* 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_*.
>

Done. With this change we don't need get_template_parms_num_siblings
anymore either so I have removed it too.

> You need more testcases.

I have added some more.

I fully bootstrapped and tested the patch on x86_64-unknown-linux-gnu.

Thanks.
Jason Merrill - Oct. 20, 2010, 2:49 p.m.
On 10/15/2010 11:44 AM, Dodji Seketeli wrote:
>> Also, don't we need to handle default template template arguments?
>
> I am not sure about this but can a default template template argument
> depend on the template parms of the current template being declared?

Well, yes, as in the example I gave with that question:

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

> template<class T>
> struct C
> {
> };
>
> template<class U,
> 	 template<class V>  class W = C>
> struct S
> {
> };
>
> Here, the template parms of C haven't been created in the template parm
> list of S. Furthermore, couldn't tsubsting U into C would wrongly
> remplace the template parm T of C with U? I said wrongly because now
> with this patch T and U are different types.

Right, we don't want to modify C.  Doesn't tsubst_template_arg do the 
right thing?  It looks to me like it ends up calling tsubst_copy, which 
should return C unchanged.

Actually, I guess you can use tsubst_template_arg for all three 
varieties of template parameter, rather than handle each one specifically.

Jason

Patch

diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index f76c2be..d03b5b1 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -6690,7 +6690,7 @@  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 626e452..1c009e5 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;
@@ -4306,6 +4307,9 @@  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)
@@ -4327,10 +4331,6 @@  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.
 
@@ -5012,7 +5012,7 @@  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);
@@ -5348,7 +5348,6 @@  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 8b2e542..0a93da8 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 3e02cd5..3d4444b 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -11018,6 +11018,13 @@  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;
@@ -11036,11 +11043,11 @@  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 a365603..7737ccc 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -137,7 +137,7 @@  static tree convert_template_argument (tree, tree, tree,
 static int for_each_template_parm (tree, tree_fn_t, void*,
 				   struct pointer_set_t*, bool);
 static tree expand_template_argument_pack (tree);
-static tree build_template_parm_index (int, int, int, tree, tree);
+static tree build_template_parm_index (int, int, int, int, tree, tree);
 static bool inline_needs_template_parms (tree);
 static void push_inline_template_parms_recursive (tree, int);
 static tree retrieve_local_specialization (tree);
@@ -190,6 +190,12 @@  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
@@ -3346,12 +3352,14 @@  check_template_shadow (tree decl)
 }
 
 /* Return a new TEMPLATE_PARM_INDEX with the indicated INDEX, LEVEL,
-   ORIG_LEVEL, DECL, and TYPE.  */
+   ORIG_LEVEL, DECL, and TYPE.  NUM_SIBLINGS is the total number of
+   template parameters.  */
 
 static tree
 build_template_parm_index (int index,
 			   int level,
 			   int orig_level,
+			   int num_siblings,
 			   tree decl,
 			   tree type)
 {
@@ -3359,6 +3367,7 @@  build_template_parm_index (int index,
   TEMPLATE_PARM_IDX (t) = index;
   TEMPLATE_PARM_LEVEL (t) = level;
   TEMPLATE_PARM_ORIG_LEVEL (t) = orig_level;
+  TEMPLATE_PARM_NUM_SIBLINGS (t) = num_siblings;
   TEMPLATE_PARM_DECL (t) = decl;
   TREE_TYPE (t) = type;
   TREE_CONSTANT (t) = TREE_CONSTANT (decl);
@@ -3370,6 +3379,7 @@  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.  */
+
 static tree
 canonical_type_parameter (tree type)
 {
@@ -3423,6 +3433,7 @@  reduce_template_parm_level (tree index, tree type, int levels, tree args,
       t = build_template_parm_index (TEMPLATE_PARM_IDX (index),
 				     TEMPLATE_PARM_LEVEL (index) - levels,
 				     TEMPLATE_PARM_ORIG_LEVEL (index),
+				     TEMPLATE_PARM_NUM_SIBLINGS (index),
 				     decl, type);
       TEMPLATE_PARM_DESCENDANTS (index) = t;
       TEMPLATE_PARM_PARAMETER_PACK (t) 
@@ -3438,15 +3449,20 @@  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 shall
+   be set to 0.  */
 
 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;
@@ -3521,6 +3537,7 @@  process_template_parm (tree list, location_t parm_loc, tree parm, bool is_non_ty
       DECL_INITIAL (parm) = DECL_INITIAL (decl)
 	= build_template_parm_index (idx, processing_template_decl,
 				     processing_template_decl,
+				     num_template_parms,
 				     decl, TREE_TYPE (parm));
 
       TEMPLATE_PARM_PARAMETER_PACK (DECL_INITIAL (parm)) 
@@ -3554,6 +3571,7 @@  process_template_parm (tree list, location_t parm_loc, tree parm, bool is_non_ty
       TEMPLATE_TYPE_PARM_INDEX (t)
 	= build_template_parm_index (idx, processing_template_decl,
 				     processing_template_decl,
+				     num_template_parms,
 				     decl, TREE_TYPE (parm));
       TEMPLATE_TYPE_PARAMETER_PACK (t) = is_parameter_pack;
       TYPE_CANONICAL (t) = canonical_type_parameter (t);
@@ -3586,16 +3604,323 @@  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),
+				   num_parms,
+				   decl, t);
+  TEMPLATE_PARM_DESCENDANTS (idx) = TEMPLATE_PARM_DESCENDANTS (orig_idx);
+  TEMPLATE_PARM_PARAMETER_PACK (idx) = TEMPLATE_PARM_PARAMETER_PACK (orig_idx);
+  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);
+
+  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),
+				     num_parms,
+				     decl, type);
+
+  TEMPLATE_PARM_DESCENDANTS (index) = TEMPLATE_PARM_DESCENDANTS (i);
+  TEMPLATE_PARM_PARAMETER_PACK (index) = TEMPLATE_PARM_PARAMETER_PACK (i);
+
+  type = tsubst (type, args, tf_none, NULL_TREE);
+  
+  TREE_TYPE (decl) = type;
+  TREE_TYPE (index) = type;
+
+  return index;
+}
+
+/* 
+   This is a subroutine of fixup_template_parms.
+
+   It computes the canonical type of the type of the template
+   parameter PARM_DESC and update all references to that type so that
+   they use the newly computed canonical type. PARM_DESC is a
+   TREE_LIST which TREE_VALUE is the template parameter and its
+   TREE_PURPOSE is the default argument of the template parm if
+   any. IDX is the index of the template parameter, starting at
+   0. NUM_PARMS is the number of template parameters in the set
+   PARM_DESC belongs to. ARGLIST is a TREE_VEC containing the full set
+   of template parameters in a form suitable to be passed to substs
+   functions as their ARGS argument. This is what
+   current_template_args returns for a given template. The innermost
+   vector of args in ARGLIST is the set of template parms that have
+   been fixed up so far. This function adds the fixed up parameter
+   into that vector.  */
+
+static void
+fixup_template_parm (tree parm_desc,
+		     int idx,
+		     int num_parms,
+		     tree arglist)
+{
+  tree parm = TREE_VALUE (parm_desc);
+  tree fixedup_args = INNERMOST_TEMPLATE_ARGS (arglist);
+
+  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, idx) = template_parm_to_arg (parm_desc);
+
+      if (TREE_PURPOSE (parm_desc))
+	{
+	  /* 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 (parm_desc);
+
+	  if (TYPE_P (default_arg)
+	      && !dependent_type_p (default_arg))
+	    return;
+
+	  TREE_PURPOSE (parm_desc) =
+	    tsubst (default_arg, arglist,
+		    tf_warning_or_error, parm);
+	}
+    }
+  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, idx) =
+	template_parm_to_arg (parm_desc);
+
+      /* 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 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;
+
+	  fixup_template_parm (parameter, j,
+			       TREE_VEC_LENGTH (tparms),
+			       targs);
+	}
+    }
+  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);
+
+      /* Let's fix up the TEMPLATE_PARM_INDEX then. Note that we must
+	 fixup the type of PUSHED_DECL as well and luckily
+	 fixup_template_parm_index does it for us too.  */
+      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, idx) =
+	template_parm_to_arg (parm_desc);
+      TREE_TYPE (parm) = tsubst (TREE_TYPE (parm), arglist,
+				 tf_warning_or_error, NULL_TREE);
+    }
+}
+
+/* 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 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)
+    fixup_template_parm (TREE_VEC_ELT (parameter_vec, i),
+			 i, num_parms, arglist);
+}
+
 /* end_template_decl is called after a template declaration is seen.  */
 
 void
@@ -3613,6 +3938,65 @@  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 +4023,7 @@  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));
@@ -3707,6 +4035,22 @@  current_template_args (void)
 	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;
 }
 
@@ -8741,8 +9085,6 @@  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;
@@ -8752,18 +9094,8 @@  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 =
@@ -8777,6 +9109,36 @@  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);
+}
+
 /* 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
@@ -14717,6 +15079,7 @@  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));
@@ -14751,7 +15114,7 @@  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,
@@ -18425,7 +18788,7 @@  make_auto (void)
   TYPE_STUB_DECL (au) = TYPE_NAME (au);
   TEMPLATE_TYPE_PARM_INDEX (au) = build_template_parm_index
     (0, processing_template_decl + 1, processing_template_decl + 1,
-     TYPE_NAME (au), NULL_TREE);
+     0, TYPE_NAME (au), NULL_TREE);
   TYPE_CANONICAL (au) = canonical_type_parameter (au);
   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 93d13a1..a1ed527 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 ca832c6..cb6ee57 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -1143,120 +1143,30 @@  comp_array_types (const_tree t1, const_tree t2, bool allow_redeclaration)
 static bool
 comp_template_parms_position (tree t1, tree t2)
 {
+  tree index1, index2;
   gcc_assert (t1 && t2
 	      && TREE_CODE (t1) == TREE_CODE (t2)
 	      && (TREE_CODE (t1) == BOUND_TEMPLATE_TEMPLATE_PARM
 		  || 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);
+  index1 = TEMPLATE_TYPE_PARM_INDEX (TYPE_MAIN_VARIANT (t1));
+  index2 = TEMPLATE_TYPE_PARM_INDEX (TYPE_MAIN_VARIANT (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 (TEMPLATE_PARM_NUM_SIBLINGS (index1)
+      != TEMPLATE_PARM_NUM_SIBLINGS (index2))
     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_PARM_IDX (index1) != TEMPLATE_PARM_IDX (index2)
+      || TEMPLATE_PARM_LEVEL (index1) != TEMPLATE_PARM_LEVEL (index2)
+      || (TEMPLATE_PARM_PARAMETER_PACK (index1)
+	  != TEMPLATE_PARM_PARAMETER_PACK (index2)))
     return false;
 
-  /* And now compare the mighty template parms!  */
-  return !comp_template_parms (tparms1, tparms2);
+  return true;
 }
 
 /* Subroutine in comptypes.  */
@@ -1301,12 +1211,6 @@  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).  */
@@ -1407,8 +1311,10 @@  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/canon-type-10.C b/gcc/testsuite/g++.dg/template/canon-type-10.C
new file mode 100644
index 0000000..0c38946
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/canon-type-10.C
@@ -0,0 +1,23 @@ 
+// Contributed by Dodji Seketeli <dodji@redhat.com>
+// { dg-do "compile" }
+
+template<class T>
+struct C
+{
+};
+
+template<class T,
+	 template<class TT_T0, template<class TT_T1> class TT_TT> class TT,
+	 class U = TT<int, C> >
+struct S
+{
+  void foo(TT<T, C>);
+};
+
+template<class T,
+	 template<class TT_T0, template<class TT_T1> class TT_TT> class TT,
+	 class U>
+void
+S<T, TT, U>::foo(TT<T, C>)
+{
+}
diff --git a/gcc/testsuite/g++.dg/template/canon-type-11.C b/gcc/testsuite/g++.dg/template/canon-type-11.C
new file mode 100644
index 0000000..698fe31
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/canon-type-11.C
@@ -0,0 +1,39 @@ 
+// Contributed by Dodji Seketeli <dodji@redhat.com>
+// { dg-do "compile" }
+
+template<class T>
+struct C
+{
+  void bar();
+};
+
+template<class T>
+void
+C<T>::bar()
+{
+}
+
+
+template<class U,
+	 template<class TT0_T0> class TT0 = C,
+	 template<class TT1_T0> class TT1 = TT0>
+struct S
+{
+  C<U> s;
+
+  void foo(TT1<U>);
+
+  void bar()
+  {
+    foo(s);
+  }
+};
+
+template<class T,
+	 template<class TT0_T0> class TT0,
+	 template<class TT1_T0> class TT1>
+void
+S<T, TT0, TT1>::foo(TT1<T>)
+{
+  C<T> c;
+}
diff --git a/gcc/testsuite/g++.dg/template/canon-type-9.C b/gcc/testsuite/g++.dg/template/canon-type-9.C
new file mode 100644
index 0000000..de6170e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/canon-type-9.C
@@ -0,0 +1,18 @@ 
+// Contributed by Dodji Seketeli <dodji@redhat.com>
+// { dg-options "-std=c++0x" }
+// { dg-do "compile" }
+
+struct F { F(int) {}};
+
+template<class T, T* u>
+struct S
+{
+  decltype(u) foo(T);
+};
+
+template<class T, T *u>
+T* S<T, u>::foo(T)
+{
+  T t;
+  return t;
+}
diff --git a/gcc/testsuite/g++.dg/template/typedef36.C b/gcc/testsuite/g++.dg/template/typedef36.C
new file mode 100644
index 0000000..318deef
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/typedef36.C
@@ -0,0 +1,23 @@ 
+// Origin: PR c++/45606
+// { dg-do compile }
+
+template<class T, class U = int>
+struct S0
+{
+  typedef int const_iterator;
+};
+
+template<class T>
+struct Test
+{
+  typedef S0<T> SAlias;
+  typedef typename SAlias::const_iterator const_iterator;
+  const_iterator begin ();
+};
+
+template<class T>
+typename S0<T>::const_iterator
+Test<T>::begin()
+{
+  return 0;
+}