c++: mangle function template constraints

Per https://github.com/itanium-cxx-abi/cxx-abi/issues/24 and
https://github.com/itanium-cxx-abi/cxx-abi/pull/166

We need to mangle constraints to be able to distinguish between function
templates that only differ in constraints.  From the latter link, we want to
use the template parameter mangling previously specified for lambdas to also
make explicit the form of a template parameter where the argument is not a
"natural" fit for it, such as when the parameter is constrained or deduced.

I'm concerned about how the latter link changes the mangling for some C++98
and C++11 patterns, so I've limited template_parm_natural_p to avoid two
cases found by running the testsuite with -Wabi forced on:

template <class T, T V> T f() { return V; }
int main() { return f<int,42>(); }

template <int i> int max() { return i; }
template <int i, int j, int... rest> int max()
{
  int sub = max<j, rest...>();
  return i > sub ? i : sub;
}
int main() {  return max<1,2,3>(); }

A third C++11 pattern is changed by this patch:

template <template <typename...> class TT, typename... Ts> TT<Ts...> f();
template <typename> struct A { };
int main() { f<A,int>(); }

I aim to resolve these with the ABI committee before GCC 14.1.

We also need to resolve https://github.com/itanium-cxx-abi/cxx-abi/issues/38
(mangling references to dependent template-ids where the name is fully
resolved) as references to concepts in std:: will consistently run into this
area.  This is why mangle-concepts1.C only refers to concepts in the global
namespace so far.

The library changes are to avoid trying to mangle builtins, which fails.

Demangler support and test coverage is not complete yet.

gcc/cp/ChangeLog:

	* cp-tree.h (TEMPLATE_ARGS_TYPE_CONSTRAINT_P): New.
	(get_concept_check_template): Declare.
	* constraint.cc (combine_constraint_expressions)
	(finish_shorthand_constraint): Use UNKNOWN_LOCATION.
	* pt.cc (convert_generic_types_to_packs): Likewise.
	* mangle.cc (write_constraint_expression)
	(write_tparms_constraints, write_type_constraint)
	(template_parm_natural_p, write_requirement)
	(write_requires_expr): New.
	(write_encoding): Mangle trailing requires-clause.
	(write_name): Pass parms to write_template_args.
	(write_template_param_decl): Factor out from...
	(write_closure_template_head): ...here.
	(write_template_args): Mangle non-natural parms
	and requires-clause.
	(write_expression): Handle REQUIRES_EXPR.

include/ChangeLog:

	* demangle.h (enum demangle_component_type): Add
	DEMANGLE_COMPONENT_CONSTRAINTS.

libiberty/ChangeLog:

	* cp-demangle.c (d_make_comp): Handle
	DEMANGLE_COMPONENT_CONSTRAINTS.
	(d_count_templates_scopes): Likewise.
	(d_print_comp_inner): Likewise.
	(d_maybe_constraints): New.
	(d_encoding, d_template_args_1): Call it.
	(d_parmlist): Handle 'Q'.
	* testsuite/demangle-expected: Add some constraint tests.

libstdc++-v3/ChangeLog:

	* include/std/bit: Avoid builtins in requires-clauses.
	* include/std/variant: Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/abi/mangle10.C: Disable compat aliases.
	* g++.dg/abi/mangle52.C: Specify ABI 18.
	* g++.dg/cpp2a/class-deduction-alias3.C
	* g++.dg/cpp2a/class-deduction-alias8.C:
	Avoid builtins in requires-clauses.
	* g++.dg/abi/mangle-concepts1.C: New test.
	* g++.dg/abi/mangle-ttp1.C: New test.

10 files changed, 472 insertions, 47 deletions

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 64b64e1..d9972d6 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -240,7 +240,9 @@ combine_constraint_expressions (tree lhs, tree rhs)
     return rhs;
   if (!rhs)
     return lhs;
-  return finish_constraint_and_expr (input_location, lhs, rhs);
+  /* Use UNKNOWN_LOCATION so write_template_args can tell the difference
+     between this and a && the user wrote.  */
+  return finish_constraint_and_expr (UNKNOWN_LOCATION, lhs, rhs);
 }
 
 /* Extract the template-id from a concept check. For standard and variable
@@ -1605,9 +1607,11 @@ finish_shorthand_constraint (tree decl, tree constr)
     check = ovl_make (tmpl);
   check = build_concept_check (check, arg, args, tf_warning_or_error);
 
-  /* Make the check a fold-expression if needed.  */
+  /* Make the check a fold-expression if needed.
+     Use UNKNOWN_LOCATION so write_template_args can tell the
+     difference between this and a fold the user wrote.  */
   if (apply_to_each_p && declared_pack_p)
-    check = finish_left_unary_fold_expr (DECL_SOURCE_LOCATION (decl),
+    check = finish_left_unary_fold_expr (UNKNOWN_LOCATION,
 					 check, TRUTH_ANDIF_EXPR);
 
   return check;
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 8809842..b9adc17 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -3799,6 +3799,12 @@ struct GTY(()) lang_decl {
   : TREE_VEC_LENGTH (INNERMOST_TEMPLATE_ARGS (NODE))
 #endif
 
+/* True iff NODE represents the template args for a type-constraint,
+   in which case the first one represents the constrained type.
+   Currently only set during mangling.  */
+#define TEMPLATE_ARGS_TYPE_CONSTRAINT_P(NODE) \
+  TREE_PRIVATE (TREE_VEC_CHECK (NODE))
+
 /* The list of access checks that were deferred during parsing
    which need to be performed at template instantiation time.
 
@@ -8509,6 +8515,7 @@ struct processing_constraint_expression_sentinel
 extern bool processing_constraint_expression_p	();
 
 extern tree unpack_concept_check		(tree);
+extern tree get_concept_check_template		(tree);
 extern tree evaluate_concept_check              (tree);
 extern bool constraints_satisfied_p		(tree, tree = NULL_TREE);
 extern bool* lookup_subsumption_result          (tree, tree);
diff --git a/gcc/cp/mangle.cc b/gcc/cp/mangle.cc
index 5137305..8a44b11 100644
--- a/gcc/cp/mangle.cc
+++ b/gcc/cp/mangle.cc
@@ -221,7 +221,7 @@ static void write_function_type (const tree);
 static void write_bare_function_type (const tree, const int, const tree);
 static void write_method_parms (tree, const int, const tree);
 static void write_class_enum_type (const tree);
-static void write_template_args (tree);
+static void write_template_args (tree, tree = NULL_TREE);
 static void write_expression (tree);
 static void write_template_arg_literal (const tree);
 static void write_template_arg (tree);
@@ -842,6 +842,70 @@ mangle_return_type_p (tree decl)
 	  && maybe_template_info (decl));
 }
 
+/* <constraint-expression> ::= <expression> */
+
+static void
+write_constraint_expression (tree expr)
+{
+  write_expression (expr);
+}
+
+/* Mangle a requires-clause following a template-head, if any.
+
+   Q <constraint_expression> E  */
+
+static void
+write_tparms_constraints (tree constraints)
+{
+  /* In a declaration with shorthand constraints in the template-head, followed
+     by a requires-clause, followed by shorthand constraints in the
+     function-parameter-list, the full constraints will be some && with the
+     parameter constraints on the RHS, around an && with the requires-clause on
+     the RHS.  Find the requires-clause, if any.
+
+     This logic relies on the && and ... from combine_constraint_expressions,
+     finish_shorthand_constraint, and convert_generic_types_to_packs having
+     UNKNOWN_LOCATION.  If they need to have an actual location, we could move
+     to using a TREE_LANG_FLAG.  */
+  if (constraints && abi_check (19))
+    {
+      tree probe = constraints;
+      while (probe
+	     && !EXPR_LOCATION (probe)
+	     && TREE_CODE (probe) == TRUTH_ANDIF_EXPR)
+	{
+	  tree op1 = TREE_OPERAND (probe, 1);
+	  probe = (EXPR_LOCATION (op1) ? op1
+		   : TREE_OPERAND (probe, 0));
+	}
+      if (probe && EXPR_LOCATION (probe))
+	{
+	  write_char ('Q');
+	  write_constraint_expression (probe);
+	}
+    }
+}
+
+/* <type-constraint> ::= <name> */
+
+static void
+write_type_constraint (tree cnst)
+{
+  if (!cnst) return;
+
+  cnst = unpack_concept_check (cnst);
+  gcc_checking_assert (TREE_CODE (cnst) == TEMPLATE_ID_EXPR);
+
+  tree concept_decl = get_concept_check_template (cnst);
+  write_name (concept_decl, 0);
+  tree args = TREE_OPERAND (cnst, 1);
+  if (TREE_VEC_LENGTH (args) > 1)
+    {
+      TEMPLATE_ARGS_TYPE_CONSTRAINT_P (args) = true;
+      write_template_args (args);
+    }
+}
+
 /*   <encoding>		::= <function name> <bare-function-type>
 			::= <data name>  */
 
@@ -886,6 +950,14 @@ write_encoding (const tree decl)
 				mangle_return_type_p (decl),
 				d);
 
+      if (tree c = get_trailing_function_requirements (decl))
+	if (abi_check (19))
+	  {
+	    ++G.parm_depth;
+	    write_char ('Q');
+	    write_constraint_expression (c);
+	    --G.parm_depth;
+	  }
     }
 }
 
@@ -1037,7 +1109,13 @@ write_name (tree decl, const int ignore_local_scope)
 	{
 	  /* Yes: use <unscoped-template-name>.  */
 	  write_unscoped_template_name (TI_TEMPLATE (info));
-	  write_template_args (TI_ARGS (info));
+	  /* Pass down the parms of a function template in case we need to
+	     mangle them; we don't mangle the parms of a non-overloadable
+	     template.  */
+	  tree parms = (TREE_CODE (decl) == FUNCTION_DECL
+			? DECL_TEMPLATE_PARMS (TI_TEMPLATE (info))
+			: NULL_TREE);
+	  write_template_args (TI_ARGS (info), parms);
 	}
       else
 	/* Everything else gets an <unqualified-name>.  */
@@ -1722,10 +1800,136 @@ write_unnamed_type_name (const tree type)
   write_compact_number (discriminator);
 }
 
+/* ABI issue #47: if a function template parameter is not "natural" for its
+   argument we must mangle the parameter.  */
+
+static bool
+template_parm_natural_p (tree arg, tree parm)
+{
+  tree decl = TREE_VALUE (parm);
+
+  /* A template parameter is "natural" if: */
+
+  if (template_parameter_pack_p (decl))
+    {
+      tree args = ARGUMENT_PACK_ARGS (arg);
+      if (TREE_VEC_LENGTH (args) == 0)
+	{
+#if 0
+	  /* the argument is an empty pack and the parameter is an
+	     unconstrained template type parameter pack; */
+	  if (TREE_CODE (decl) != TYPE_DECL)
+	    return false;
+#else
+	  /* Defer changing the mangling of C++11 code like
+	     template <int i> int max();
+	     template <int i, int j, int... rest> int max();  */
+	  return true;
+#endif
+	}
+      else
+	/* the argument is a non-empty pack and a non-pack variant of the
+	   parameter would be natural for the first element of the pack; */
+	arg = TREE_VEC_ELT (args, 0);
+    }
+
+  /* the argument is a template and the parameter has the exact
+     same template head; */
+  if (TREE_CODE (decl) == TEMPLATE_DECL)
+    return template_heads_equivalent_p (arg, decl);
+
+  /* the argument is a type and the parameter is unconstrained; or */
+  else if (TREE_CODE (decl) == TYPE_DECL)
+    return !TEMPLATE_PARM_CONSTRAINTS (parm);
+
+  /* the argument is a non-type template argument and the declared parameter
+     type neither is instantiation dependent nor contains deduced types.  */
+  else if (TREE_CODE (decl) == PARM_DECL)
+    {
+#if 0
+      return !uses_template_parms (TREE_TYPE (decl));
+#else
+      /* Defer changing the mangling of C++98 code like
+	 template <class T, T V> ....  */
+      return !type_uses_auto (TREE_TYPE (decl));
+#endif
+    }
+
+  gcc_unreachable ();
+}
+
+/* Used for lambda template head and non-natural function template parameters.
+
+   <template-param-decl> ::= Ty               # template type parameter
+	::= Tk <type-constraint>              # constrained type parameter
+	::= Tn <type>                         # template non-type parameter
+	::= Tt <template-param-decl>* [Q <constraint-expression] E  # ttp
+	::= Tp <non-pack template-param-decl> # template parameter pack */
+
+static void
+write_template_param_decl (tree parm)
+{
+  tree decl = TREE_VALUE (parm);
+
+  if (template_parameter_pack_p (decl))
+    write_string ("Tp");
+
+  switch (TREE_CODE (decl))
+    {
+    case PARM_DECL:
+      {
+	write_string ("Tn");
+
+	tree type = TREE_TYPE (decl);
+	if (tree c = (is_auto (type)
+		      ? PLACEHOLDER_TYPE_CONSTRAINTS (type)
+		      : NULL_TREE))
+	  {
+	    if (AUTO_IS_DECLTYPE (type))
+	      write_string ("DK");
+	    else
+	      write_string ("Dk");
+	    write_type_constraint (c);
+	  }
+	else
+	  write_type (type);
+      }
+      break;
+
+    case TEMPLATE_DECL:
+      {
+	write_string ("Tt");
+	tree parms = DECL_INNERMOST_TEMPLATE_PARMS (decl);
+	for (tree node : tree_vec_range (parms))
+	  write_template_param_decl (node);
+	write_char ('E');
+      }
+      break;
+
+    case TYPE_DECL:
+      if (tree c = TEMPLATE_PARM_CONSTRAINTS (parm))
+	{
+	  if (TREE_CODE (c) == UNARY_LEFT_FOLD_EXPR)
+	    {
+	      c = FOLD_EXPR_PACK (c);
+	      c = PACK_EXPANSION_PATTERN (c);
+	    }
+	  if (TREE_CODE (decl) == TYPE_DECL)
+	    {
+	      write_string ("Tk");
+	      write_type_constraint (c);
+	    }
+	}
+      else
+	write_string ("Ty");
+      break;
+
+    default:
+      gcc_unreachable ();
+    }
+}
+
 // A template head, for templated lambdas.
-// <template-head> ::=   Tp* Ty
-//                       Tp* Tn <type>
-//                       Tp* Tt <template-head> E
 // New in ABI=18. Returns true iff we emitted anything -- used for ABI
 // version warning.
 
@@ -1735,50 +1939,26 @@ write_closure_template_head (tree tmpl)
   bool any = false;
 
   // We only need one level of template parms
-  tree inner = INNERMOST_TEMPLATE_PARMS (DECL_TEMPLATE_PARMS (tmpl));
+  tree parms = DECL_TEMPLATE_PARMS (tmpl);
+  tree inner = INNERMOST_TEMPLATE_PARMS (parms);
 
   for (int ix = 0, len = TREE_VEC_LENGTH (inner); ix != len; ix++)
     {
       tree parm = TREE_VEC_ELT (inner, ix);
       if (parm == error_mark_node)
 	continue;
-      parm = TREE_VALUE (parm);
 
-      if (DECL_IMPLICIT_TEMPLATE_PARM_P (parm))
+      if (DECL_IMPLICIT_TEMPLATE_PARM_P (TREE_VALUE (parm)))
 	// A synthetic parm, we're done.
 	break;
 
       any = true;
       if (abi_version_at_least (18))
-	{
-	  if (TREE_CODE (parm) == PARM_DECL
-	      ? TEMPLATE_PARM_PARAMETER_PACK (DECL_INITIAL (parm))
-	      : TEMPLATE_TYPE_PARAMETER_PACK (TREE_TYPE (parm)))
-	    write_string ("Tp");
-
-	  switch (TREE_CODE (parm))
-	    {
-	    default:
-	      gcc_unreachable ();
-
-	    case TYPE_DECL:
-	      write_string ("Ty");
-	      break;
-
-	    case PARM_DECL:
-	      write_string ("Tn");
-	      write_type (TREE_TYPE (parm));
-	      break;
-
-	    case TEMPLATE_DECL:
-	      write_string ("Tt");
-	      write_closure_template_head (parm);
-	      write_string ("E");
-	      break;
-	    }
-	}
+	write_template_param_decl (parm);
     }
 
+  write_tparms_constraints (TEMPLATE_PARMS_CONSTRAINTS (parms));
+
   return any;
 }
 
@@ -2893,13 +3073,84 @@ write_class_enum_type (const tree type)
   write_name (TYPE_NAME (type), /*ignore_local_scope=*/0);
 }
 
+/* Mangle a requirement REQ in a requires-expression.  */
+
+static void
+write_requirement (tree req)
+{
+  tree op = TREE_OPERAND (req, 0);
+
+  switch (tree_code code = TREE_CODE (req))
+    {
+      /* # simple-requirement or compound-requirement
+	 <requirement> ::= X <expression> [ N ] [ R <type-constraint> ] */
+    case SIMPLE_REQ:
+    case COMPOUND_REQ:
+      write_char ('X');
+      write_expression (op);
+      if (code == SIMPLE_REQ)
+	break;
+      if (COMPOUND_REQ_NOEXCEPT_P (req))
+	write_char ('N');
+      if (tree constr = TREE_OPERAND (req, 1))
+	{
+	  write_char ('R');
+	  write_type_constraint (PLACEHOLDER_TYPE_CONSTRAINTS (constr));
+	}
+      break;
+
+      /* <requirement> ::= T <type> # type-requirement */
+    case TYPE_REQ:
+      write_char ('T');
+      write_type (op);
+      break;
+
+      /* <requirement> ::= Q <constraint-expression> # nested-requirement */
+    case NESTED_REQ:
+      write_char ('Q');
+      write_constraint_expression (op);
+      break;
+
+    default:
+      gcc_unreachable ();
+    }
+}
+
+/* # requires { ... }
+   <expression> ::= rq <requirement>+ E
+   # requires (...) { ... }
+   <expression> ::= rQ <bare-function-type> _ <requirement>+ E */
+
+static void
+write_requires_expr (tree expr)
+{
+  tree parms = REQUIRES_EXPR_PARMS (expr);
+  if (parms)
+    {
+      write_string ("rQ");
+      ++G.parm_depth;
+      for (; parms; parms = DECL_CHAIN (parms))
+	write_type (cv_unqualified (TREE_TYPE (parms)));
+      --G.parm_depth;
+      write_char ('_');
+    }
+  else
+    write_string ("rq");
+
+  for (tree reqs = REQUIRES_EXPR_REQS (expr); reqs;
+       reqs = TREE_CHAIN (reqs))
+    write_requirement (TREE_VALUE (reqs));
+
+  write_char ('E');
+}
+
 /* Non-terminal <template-args>.  ARGS is a TREE_VEC of template
    arguments.
 
-     <template-args> ::= I <template-arg>* E  */
+     <template-args> ::= I <template-arg>* [Q <constraint-expr>] E  */
 
 static void
-write_template_args (tree args)
+write_template_args (tree args, tree parms /*= NULL_TREE*/)
 {
   int i;
   int length = 0;
@@ -2911,6 +3162,13 @@ write_template_args (tree args)
   if (args)
     length = TREE_VEC_LENGTH (args);
 
+  tree constraints = NULL_TREE;
+  if (parms)
+    {
+      constraints = TEMPLATE_PARMS_CONSTRAINTS (parms);
+      parms = INNERMOST_TEMPLATE_PARMS (parms);
+    }
+
   if (args && length && TREE_CODE (TREE_VEC_ELT (args, 0)) == TREE_VEC)
     {
       /* We have nested template args.  We want the innermost template
@@ -2918,8 +3176,38 @@ write_template_args (tree args)
       args = TREE_VEC_ELT (args, length - 1);
       length = TREE_VEC_LENGTH (args);
     }
-  for (i = 0; i < length; ++i)
-    write_template_arg (TREE_VEC_ELT (args, i));
+  if (TEMPLATE_ARGS_TYPE_CONSTRAINT_P (args))
+    /* Skip the constrained type.  */
+    i = 1;
+  else
+    i = 0;
+  bool implicit_parm_scope = false;
+  for (; i < length; ++i)
+    {
+      tree arg = TREE_VEC_ELT (args, i);
+      if (parms)
+	{
+	  tree parm = TREE_VEC_ELT (parms, i);
+	  tree decl = TREE_VALUE (parm);
+	  if (DECL_IMPLICIT_TEMPLATE_PARM_P (decl)
+	      && !implicit_parm_scope)
+	    {
+	      /* The rest of the template parameters are based on generic
+		 function parameters, so any expressions in their
+		 type-constraints are in parameter scope.  */
+	      implicit_parm_scope = true;
+	      ++G.parm_depth;
+	    }
+	  if (!template_parm_natural_p (arg, parm)
+	      && abi_check (19))
+	    write_template_param_decl (parm);
+	}
+      write_template_arg (arg);
+    }
+  if (implicit_parm_scope)
+    --G.parm_depth;
+
+  write_tparms_constraints (constraints);
 
   write_char ('E');
 }
@@ -3107,6 +3395,7 @@ write_expression (tree expr)
       write_char ('f');
       if (delta != 0)
 	{
+	  gcc_checking_assert (delta > 0);
 	  if (abi_check (5))
 	    {
 	      /* Let L be the number of function prototype scopes from the
@@ -3431,6 +3720,8 @@ write_expression (tree expr)
       write_type (LAMBDA_EXPR_CLOSURE (expr));
       write_char ('E');
     }
+  else if (code == REQUIRES_EXPR)
+    write_requires_expr (expr);
   else if (dependent_name (expr))
     {
       tree name = dependent_name (expr);
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index c54b256..d12d576 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -30951,7 +30951,9 @@ convert_generic_types_to_packs (tree parm, int start_idx, int end_idx)
 	{
 	  tree id = unpack_concept_check (constr);
 	  TREE_VEC_ELT (TREE_OPERAND (id, 1), 0) = t;
-	  location_t loc = DECL_SOURCE_LOCATION (TYPE_NAME (t));
+	  /* Use UNKNOWN_LOCATION so write_template_args can tell the
+	     difference between this and a fold the user wrote.  */
+	  location_t loc = UNKNOWN_LOCATION;
 	  tree fold = finish_left_unary_fold_expr (loc, constr,
 						   TRUTH_ANDIF_EXPR);
 	  TEMPLATE_PARM_CONSTRAINTS (node) = fold;
diff --git a/gcc/testsuite/g++.dg/abi/mangle-concepts1.C b/gcc/testsuite/g++.dg/abi/mangle-concepts1.C
new file mode 100644
index 0000000..eac520c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/abi/mangle-concepts1.C
@@ -0,0 +1,88 @@
+// { dg-do compile { target c++20 } }
+
+template <class T> concept C = true;
+template <class T, class U> concept C2 = true;
+template <class T> concept D = true;
+template <class T> concept E = true;
+template <class T> concept F = true;
+template <class T> using Ref = T&;
+
+// { dg-final { scan-assembler "_Z1fIiQ1CIT_EEvv" } }
+template <class T> requires C<T> void f() {}
+template void f<int>();
+
+// { dg-final { scan-assembler "_Z2f2ITk1CiEvv" } }
+template <C T> void f2() {}
+template void f2<int>();
+
+// { dg-final { scan-assembler "_Z2f3IiEvvQ1CIT_E" } }
+template <class T> void f3() requires C<T> {}
+template void f3<int>();
+
+// { dg-final { scan-assembler "_Z2f4ITk1CiEvT_" } }
+void f4(C auto c) {}
+template void f4(int);
+
+// ??? The constraints end up out of order in the mangled name, may
+// need to change the equivalence rule.
+// { dg-final { scan-assembler "_Z2f5ITk1CicTk1EfTk1FsQ1DIT0_EEvT1_T2_" } }
+template <C T, class U> requires D<U> void f5(E auto c, F auto f) {}
+template void f5<int,char>(float,short);
+
+// { dg-final { scan-assembler "_Z2f6ITk2C2IiEsEvv" } }
+template <C2<int> T> void f6() {}
+template void f6<short>();
+
+// { dg-final { scan-assembler "_ZN1AIiE1fEvQ1CIT_E" } }
+template <class T> struct A {
+  void f() requires C<T> { };
+};
+template struct A<int>;
+
+// { dg-final { scan-assembler "_Z1gIiQrqXcvT__ETRS0_Q1CIS0_EXpscvS0__ENR1CEEvv" } }
+template <class T>
+requires requires { T();
+		    typename Ref<T>;
+		    requires C<T>;
+		    { +T() } noexcept -> C;
+}
+void g() {}
+template void g<int>();
+
+// { dg-final { scan-assembler "_Z1hIiQrQT__Xpsfp_EEvv" } }
+template <class T>
+requires requires (T t) { +t; }
+void h() {}
+template void h<int>();
+
+// { dg-final { scan-assembler "_Z3fn1IiEvT_QrQS0__XpsfL0p_Xpsfp_E" } }
+template <class T>
+void fn1(T t1)
+  requires requires (T t2) { +t1; +t2; }
+{}
+template void fn1<int>(int);
+
+// { dg-final { scan-assembler "_Z3fn3IiTk2C2IDtfL0p_EEiEvT_T0_" } }
+template<typename T> void fn3(T t, C2<decltype(t)> auto) {}
+template void fn3(int, int);
+
+// { dg-final { scan-assembler "_Z3fn4IiiEvT_T0_Q2C2IS1_FDTcl3fn3fL0p_fp_EES0_EE" } }
+template<typename T, typename U> void fn4(T t, U u)
+  requires C2<U, auto (T u) -> decltype(fn3(t, u))> {}
+template void fn4(int, int);
+
+// { dg-final { scan-assembler "_Z3fn5ITpTk1CJicfEEvDpT_" } }
+template<C... T> void fn5(T...) { }
+template void fn5(int,char,float);
+
+// { dg-final { scan-assembler "_ZN2A2IiE1BIiE1fIiiEEvvQ2C2IT_TL1_0_E" } }
+template <class T> struct A2 {
+  template <class X> struct B {
+    template <class U, class V> void f() requires C2<T,V> {}
+  };
+};
+template void A2<int>::B<int>::f<int,int>();
+
+template<C auto N> void f7() {}
+// { dg-final { scan-assembler "_Z2f7ITnDk1CLi5EEvv" } }
+template void f7<5>();
diff --git a/gcc/testsuite/g++.dg/abi/mangle-ttp1.C b/gcc/testsuite/g++.dg/abi/mangle-ttp1.C
new file mode 100644
index 0000000..2f5878f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/abi/mangle-ttp1.C
@@ -0,0 +1,27 @@
+// ABI #47 "natural" template parameter mangling
+// { dg-do compile { target c++17 } }
+
+template <template <class...> class TT> class A { };
+template <int... T> class B { };
+
+template <auto... T>
+void f(B<T...> b);
+
+template <template <auto...> class TT>
+void g(TT<42>);
+
+template <template <int...> class TT>
+void h(TT<42>);
+
+template <class T> struct C {
+  template <template <T...> class TT> static void j(TT<42>);
+};
+
+int main()
+{
+  B<42> b;
+  f(b); // { dg-final { scan-assembler "_Z1fITpTnDaJLi42EEEv1BIJXspT_EEE" } }
+  g(b); // { dg-final { scan-assembler "_Z1gITtTpTnDaE1BEvT_IJLi42EEE" } }
+  h(b); // { dg-final { scan-assembler "_Z1hI1BEvT_IJLi42EEE" } }
+  C<int>::j(b); // { dg-final { scan-assembler "_ZN1CIiE1jI1BEEvT_IJLi42EEE" } }
+}
diff --git a/gcc/testsuite/g++.dg/abi/mangle10.C b/gcc/testsuite/g++.dg/abi/mangle10.C
index d5782ba..fcbb815 100644
--- a/gcc/testsuite/g++.dg/abi/mangle10.C
+++ b/gcc/testsuite/g++.dg/abi/mangle10.C
@@ -1,4 +1,4 @@
-// { dg-options "-fabi-version=0" }
+// { dg-options "-fabi-version=0 -fabi-compat-version=0" }
 
 template <template <typename> class Q>
 void f (typename Q<int>::X) {}
diff --git a/gcc/testsuite/g++.dg/abi/mangle52.C b/gcc/testsuite/g++.dg/abi/mangle52.C
index 0b9a72f..1e7eca0 100644
--- a/gcc/testsuite/g++.dg/abi/mangle52.C
+++ b/gcc/testsuite/g++.dg/abi/mangle52.C
@@ -1,4 +1,4 @@
-// { dg-options "-fabi-version=0 -Wabi=2" }
+// { dg-options "-fabi-version=18 -Wabi=2" }
 
 template <unsigned int> struct helper {};
 // { dg-final { scan-assembler "\n_?_Z6check1IiEvP6helperIXszscT_Li1EEE\[: \t\n\]" } }
diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias3.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias3.C
index 318d4c9..b43a8c8 100644
--- a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias3.C
+++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias3.C
@@ -1,8 +1,11 @@
 // PR c++/95486
 // { dg-do compile { target c++20 } }
 
+template <class T>
+concept Int = __is_same (T, int);
+
 template<class T, class U>
-struct X { X(U) requires __is_same(U, int) {} };
+struct X { X(U) requires Int<U> {} };
 
 template<class U>
 using Y = X<void, U>;
diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias8.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias8.C
index ec005956..9de0a72 100644
--- a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias8.C
+++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias8.C
@@ -1,8 +1,11 @@
 // PR c++/95486
 // { dg-do compile { target c++20 } }
 
+template <class T>
+concept Int = __is_same (T, int);
+
 template<class T, class U>
-struct X { X(U) requires __is_same(U, int) {} };
+struct X { X(U) requires Int<U> {} };
 
 template<class U>
 X(U) -> X<char, U>;