[gcc r15-123] c++: remove lookup_template_class's entering_scope flag

[gcc r15-123] c++: remove lookup_template_class's entering_scope flag

[Patrick Palka]

https://gcc.gnu.org/g:f04dc89a991ddc6c08ac92c8ad29c6915c4ecafa

commit r15-123-gf04dc89a991ddc6c08ac92c8ad29c6915c4ecafa
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu May 2 21:14:30 2024 -0400

    c++: remove lookup_template_class's entering_scope flag
    
    lookup_template_class's entering_scope flag controls whether to prefer
    returning the primary template type A<T> instead of the corresponding
    implicit instantiation A<T>.  When we want to set this flag as part of
    substitution, we need to use tsubst_aggr_type which also takes this flag
    as a parameter.  But having this separate entry point to type substitution
    turned out to be subtly problematic because it doesn't reuse typedefs
    like tsubst does, which r13-4729-gbe124477b38a71 fixed in a way that
    respects the flag after the fact, by adjusting the entering_scope=false
    result of lookup_template_class as if entering_scope=true was passed.
    
    But if that's possible then it means lookup_template_class's
    entering_scope flag is not necessary after all -- we can just do the
    after-the-fact adjustment everywhere that we currently pass
    entering_scope=true to it and tsubst_aggr_type.
    
    To that end, this patch replaces this flag with an adjustment function
    adjust_type_for_entering_scope, to be used whereever we currently need
    the entering_scope=true behavior.  In turn we can get rid of
    tsubst_aggr_type since the only reason we needed this entry point
    was to be able to pass entering_scope=true to lookup_template_class.
    
    gcc/cp/ChangeLog:
    
            * coroutines.cc (instantiate_coro_traits): Adjust call to
            lookup_template_class.
            (instantiate_coro_handle_for_promise_type): Likewise.
            * cp-tree.h (adjust_type_for_entering_scope): Declare.
            (lookup_template_class): Adjust declaration.
            * decl.cc (make_typename_type): Adjust call to
            lookup_template_class. Likewise.
            (get_tuple_size): Likewise.
            (get_tuple_element_type): Likewise.
            * pt.cc (adjust_type_for_entering_scope): Define.
            (tsubst_entering_scope): Define.
            (lookup_template_class): Remove entering_scope parameter.
            Replace tsubst_aggr_type call with tsubst_entering_scope.
            (tsubst_aggr_type): Remove.
            (tsubst_aggr_type_1): Inline into tsubst.
            (tsubst_function_decl): Replace tsubst_aggr_type call
            with tsubst_entering_scope.
            (tsubst_template_decl): Likewise.
            (tsubst_decl): Likewise.
            (tsubst) <case RECORD_TYPE, UNION_TYPE, ENUMERAL_TYPE>:
            Inlined from tsubst_aggr_type_1.
            <case BOUND_TEMPLATE_TEMPLATE_PARM>: Adjust calls to
            lookup_template_class.
            <case TYPENAME_TYPE>: Replace tsubst_aggr_type call with
            tsubst_entering_scope.
            <case UNBOUND_CLASS_TEMPLATE>: Likewise.
            Increment processing_template_decl when substituting the
            context.
            (tsubst_expr) <case FIELD_DECL>: Replace tsubst_aggr_type
            call with tsubst_entering_scope.
            <case TEMPLATE_DECL>: Likewise.
            (instantiate_template): Likewise.
            (resolve_typename_type): Adjust lookup_template_class call
            and call adjust_type_for_entering_scope afterward.
            (listify): Adjust lookup_template_class call.
            (alias_ctad_tweaks): Likewise.
            * semantics.cc (finish_template_type): Adjust lookup_template_class
            call and maybe call adjust_type_for_entering_scope afterward.
    
    Reviewed-by: Jason Merrill <jason@redhat.com>

Diff:
---
 gcc/cp/coroutines.cc |   4 +-
 gcc/cp/cp-tree.h     |   3 +-
 gcc/cp/decl.cc       |   4 +-
 gcc/cp/pt.cc         | 207 ++++++++++++++++++++-------------------------------
 gcc/cp/semantics.cc  |   4 +-
 5 files changed, 88 insertions(+), 134 deletions(-)

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index b05cb9eb330..97bc211ff67 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -353,7 +353,7 @@ instantiate_coro_traits (tree fndecl, location_t kw)
   tree traits_class
     = lookup_template_class (coro_traits_templ, targ,
 			     /*in_decl=*/NULL_TREE, /*context=*/NULL_TREE,
-			     /*entering scope=*/false, tf_warning_or_error);
+			     tf_warning_or_error);
 
   if (traits_class == error_mark_node)
     {
@@ -400,7 +400,7 @@ instantiate_coro_handle_for_promise_type (location_t kw, tree promise_type)
     = lookup_template_class (coro_handle_identifier, targ,
 			     /* in_decl=*/NULL_TREE,
 			     /* context=*/std_node,
-			     /* entering scope=*/false, tf_warning_or_error);
+			     tf_warning_or_error);
 
   if (handle_type == error_mark_node)
     {
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 933504b4821..1ba7054f8bc 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7524,8 +7524,9 @@ extern tree push_template_decl			(tree, bool is_friend = false);
 extern tree add_inherited_template_parms	(tree, tree);
 extern void template_parm_level_and_index	(tree, int*, int*);
 extern bool redeclare_class_template		(tree, tree, tree);
+extern tree adjust_type_for_entering_scope	(tree);
 extern tree lookup_template_class		(tree, tree, tree, tree,
-						 int, tsubst_flags_t);
+						 tsubst_flags_t);
 extern tree lookup_template_function		(tree, tree);
 extern tree lookup_template_variable		(tree, tree, tsubst_flags_t);
 extern bool uses_template_parms			(tree);
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 378311c0f04..71e4c2b5840 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -4578,7 +4578,6 @@ make_typename_type (tree context, tree name, enum tag_types tag_type,
     {
       t = lookup_template_class (t, TREE_OPERAND (fullname, 1),
 				 NULL_TREE, context,
-				 /*entering_scope=*/0,
 				 complain | tf_user);
       if (t == error_mark_node)
 	return error_mark_node;
@@ -9175,7 +9174,7 @@ get_tuple_size (tree type)
   tree inst = lookup_template_class (tuple_size_identifier, args,
 				     /*in_decl*/NULL_TREE,
 				     /*context*/std_node,
-				     /*entering_scope*/false, tf_none);
+				     tf_none);
   inst = complete_type (inst);
   if (inst == error_mark_node
       || !COMPLETE_TYPE_P (inst)
@@ -9204,7 +9203,6 @@ get_tuple_element_type (tree type, unsigned i)
   tree inst = lookup_template_class (tuple_element_identifier, args,
 				     /*in_decl*/NULL_TREE,
 				     /*context*/std_node,
-				     /*entering_scope*/false,
 				     tf_warning_or_error);
   return make_typename_type (inst, type_identifier,
 			     none_type, tf_warning_or_error);
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 1c3eef60c06..d68d688016d 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -185,8 +185,6 @@ static int unify_pack_expansion (tree, tree, tree,
 static tree copy_template_args (tree);
 static tree tsubst_template_parms (tree, tree, tsubst_flags_t);
 static void tsubst_each_template_parm_constraints (tree, tree, tsubst_flags_t);
-static tree tsubst_aggr_type (tree, tree, tsubst_flags_t, tree, int);
-static tree tsubst_aggr_type_1 (tree, tree, tsubst_flags_t, tree, int);
 static tree tsubst_arg_types (tree, tree, tree, tsubst_flags_t, tree);
 static tree tsubst_function_type (tree, tree, tsubst_flags_t, tree);
 static bool check_specialization_scope (void);
@@ -9901,6 +9899,35 @@ maybe_get_template_decl_from_type_decl (tree decl)
     ? CLASSTYPE_TI_TEMPLATE (TREE_TYPE (decl)) : decl;
 }
 
+/* If TYPE is the generic implicit instantiation A<T>, return the primary
+   template type A<T> (which is suitable for entering into, e.g. for defining
+   a member of A<T>), otherwise return TYPE.  */
+
+tree
+adjust_type_for_entering_scope (tree type)
+{
+  if (CLASS_TYPE_P (type)
+      && dependent_type_p (type)
+      && TYPE_TEMPLATE_INFO (type)
+      /* We detect the generic implicit instantiation A<T> by inspecting
+	 TYPE_CANONICAL, which lookup_template_class sets to the primary
+	 template type A<T>.  */
+      && TYPE_CANONICAL (type) == TREE_TYPE (TYPE_TI_TEMPLATE (type)))
+    type = TYPE_CANONICAL (type);
+
+  return type;
+}
+
+/* Convenience wrapper over tsubst that does adjust_type_for_entering_scope
+   on the result.  */
+
+static tree
+tsubst_entering_scope (tree t, tree args, tsubst_flags_t complain, tree in_decl)
+{
+  t = tsubst (t, args, complain, in_decl);
+  return adjust_type_for_entering_scope (t);
+}
+
 /* Given an IDENTIFIER_NODE (or type TEMPLATE_DECL) and a chain of
    parameters, find the desired type.
 
@@ -9909,9 +9936,6 @@ maybe_get_template_decl_from_type_decl (tree decl)
    IN_DECL, if non-NULL, is the template declaration we are trying to
    instantiate.
 
-   If ENTERING_SCOPE is nonzero, we are about to enter the scope of
-   the class we are looking up.
-
    Issue error and warning messages under control of COMPLAIN.
 
    If the template class is really a local class in a template
@@ -9927,7 +9951,7 @@ maybe_get_template_decl_from_type_decl (tree decl)
 
 tree
 lookup_template_class (tree d1, tree arglist, tree in_decl, tree context,
-		       int entering_scope, tsubst_flags_t complain)
+		       tsubst_flags_t complain)
 {
   auto_timevar tv (TV_TEMPLATE_INST);
 
@@ -10139,9 +10163,10 @@ lookup_template_class (tree d1, tree arglist, tree in_decl, tree context,
 	   template <class T> class C { void f(C<T>); }
 
 	 the `C<T>' is just the same as `C'.  Outside of the
-	 class, however, such a reference is an instantiation.  */
-      if (entering_scope
-	  || !PRIMARY_TEMPLATE_P (gen_tmpl)
+	 class, however, such a reference is an instantiation.
+	 One can use adjust_type_for_entering_scope to make
+	 this adjustment as needed.  */
+      if (!PRIMARY_TEMPLATE_P (gen_tmpl)
 	  || currently_open_class (template_type))
 	{
 	  tree tinfo = TYPE_TEMPLATE_INFO (template_type);
@@ -10207,8 +10232,8 @@ lookup_template_class (tree d1, tree arglist, tree in_decl, tree context,
 	    context = DECL_CONTEXT (templ);
 	  else
 	    {
-	      context = tsubst_aggr_type (context, arglist,
-					  complain, in_decl, true);
+	      context = tsubst_entering_scope (context, arglist,
+					       complain, in_decl);
 	      /* Try completing the enclosing context if it's not already so.  */
 	      if (context != error_mark_node
 		  && !COMPLETE_TYPE_P (context))
@@ -14148,94 +14173,6 @@ tsubst_each_template_parm_constraints (tree parms, tree args,
   --processing_template_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
-   ENTERING_SCOPE is nonzero, T is the context for a template which
-   we are presently tsubst'ing.  Return the substituted value.  */
-
-static tree
-tsubst_aggr_type (tree t,
-		  tree args,
-		  tsubst_flags_t complain,
-		  tree in_decl,
-		  int entering_scope)
-{
-  if (t == NULL_TREE)
-    return NULL_TREE;
-
-  /* Handle typedefs via tsubst so that they get consistently reused.  */
-  if (typedef_variant_p (t))
-    {
-      t = tsubst (t, args, complain, in_decl);
-      if (t == error_mark_node)
-	return error_mark_node;
-
-      /* The effect of entering_scope is that for a dependent specialization
-	 A<T>, lookup_template_class prefers to return A's primary template
-	 type instead of the implicit instantiation.  So when entering_scope,
-	 we mirror this behavior by inspecting TYPE_CANONICAL appropriately,
-	 taking advantage of the fact that lookup_template_class links the two
-	 types by setting TYPE_CANONICAL of the latter to the former.  */
-      if (entering_scope
-	  && CLASS_TYPE_P (t)
-	  && dependent_type_p (t)
-	  && TYPE_TEMPLATE_INFO (t)
-	  && TYPE_CANONICAL (t) == TREE_TYPE (TYPE_TI_TEMPLATE (t)))
-	t = TYPE_CANONICAL (t);
-
-      return t;
-    }
-
-  switch (TREE_CODE (t))
-    {
-      case RECORD_TYPE:
-      case ENUMERAL_TYPE:
-      case UNION_TYPE:
-	return tsubst_aggr_type_1 (t, args, complain, in_decl, entering_scope);
-
-      default:
-	return tsubst (t, args, complain, in_decl);
-    }
-}
-
-/* The part of tsubst_aggr_type that's shared with the RECORD_, UNION_
-   and ENUMERAL_TYPE cases of tsubst.  */
-
-static tree
-tsubst_aggr_type_1 (tree t,
-		    tree args,
-		    tsubst_flags_t complain,
-		    tree in_decl,
-		    int entering_scope)
-{
-  if (TYPE_TEMPLATE_INFO (t) && uses_template_parms (t))
-    {
-      complain &= ~tf_qualifying_scope;
-
-      /* Figure out what arguments are appropriate for the
-	 type we are trying to find.  For example, given:
-
-	   template <class T> struct S;
-	   template <class T, class U> void f(T, U) { S<U> su; }
-
-	 and supposing that we are instantiating f<int, double>,
-	 then our ARGS will be {int, double}, but, when looking up
-	 S we only want {double}.  */
-      tree argvec = tsubst_template_args (TYPE_TI_ARGS (t), args,
-					  complain, in_decl);
-      if (argvec == error_mark_node)
-	return error_mark_node;
-
-      tree r = lookup_template_class (t, argvec, in_decl, NULL_TREE,
-				      entering_scope, complain);
-      return cp_build_qualified_type (r, cp_type_quals (t), complain);
-    }
-  else
-    /* This is not a template type, so there's nothing to do.  */
-    return t;
-}
-
 /* Map from a FUNCTION_DECL to a vec of default argument instantiations,
    indexed in reverse order of the parameters.  */
 
@@ -14601,8 +14538,7 @@ tsubst_function_decl (tree t, tree args, tsubst_flags_t complain,
     lambda_fntype = static_fn_type (lambda_fntype);
 
   if (member && !closure)
-    ctx = tsubst_aggr_type (ctx, args,
-			    complain, t, /*entering_scope=*/1);
+    ctx = tsubst_entering_scope (ctx, args, complain, t);
 
   tree type = (lambda_fntype ? lambda_fntype
 	       : tsubst (TREE_TYPE (t), args,
@@ -14996,8 +14932,7 @@ tsubst_template_decl (tree t, tree args, tsubst_flags_t complain,
 	  inner = TREE_TYPE (inner);
 	}
       if (class_p)
-	inner = tsubst_aggr_type (inner, args, complain,
-				  in_decl, /*entering*/1);
+	inner = tsubst_entering_scope (inner, args, complain, in_decl);
       else
 	inner = tsubst_decl (inner, args, complain, /*use_spec_table=*/false);
     }
@@ -15501,9 +15436,7 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain,
 	    local_p = false;
 	    if (DECL_CLASS_SCOPE_P (t))
 	      {
-		ctx = tsubst_aggr_type (ctx, args,
-					complain,
-					in_decl, /*entering_scope=*/1);
+		ctx = tsubst_entering_scope (ctx, args, complain, in_decl);
 		if (DECL_SELF_REFERENCE_P (t))
 		  /* The context and type of an injected-class-name are
 		     the same, so we don't need to substitute both.  */
@@ -16299,8 +16232,29 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
       /* Fall through.  */
     case UNION_TYPE:
     case ENUMERAL_TYPE:
-      return tsubst_aggr_type_1 (t, args, complain, in_decl,
-				 /*entering_scope=*/0);
+      if (TYPE_TEMPLATE_INFO (t) && uses_template_parms (t))
+	{
+	  /* Figure out what arguments are appropriate for the
+	     type we are trying to find.  For example, given:
+
+	       template <class T> struct S;
+	       template <class T, class U> void f(T, U) { S<U> su; }
+
+	     and supposing that we are instantiating f<int, double>,
+	     then our ARGS will be {int, double}, but, when looking up
+	     S we only want {double}.  */
+	  tree argvec = tsubst_template_args (TYPE_TI_ARGS (t), args,
+					      complain, in_decl);
+	  if (argvec == error_mark_node)
+	    return error_mark_node;
+
+	  tree r = lookup_template_class (t, argvec, in_decl, NULL_TREE,
+					  complain);
+	  return cp_build_qualified_type (r, cp_type_quals (t), complain);
+	}
+      else
+	/* This is not a template type, so there's nothing to do.  */
+	return t;
 
     case ERROR_MARK:
     case IDENTIFIER_NODE:
@@ -16492,7 +16446,6 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 		r = lookup_template_class (arg,
 					   argvec, in_decl,
 					   DECL_CONTEXT (arg),
-					    /*entering_scope=*/0,
 					   complain);
 		return cp_build_qualified_type
 		  (r, cp_type_quals (t) | cp_type_quals (r), complain);
@@ -16584,7 +16537,7 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	      if (argvec == error_mark_node)
 		return error_mark_node;
 	      r = lookup_template_class (tmpl, argvec, in_decl, NULL_TREE,
-					 /*entering_scope=*/false, complain);
+					 complain);
 	      r = cp_build_qualified_type (r, cp_type_quals (t), complain);
 	      break;
 	    }
@@ -16839,9 +16792,9 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	    ctx = TREE_VEC_ELT (ctx, 0);
 	  }
 	else
-	  ctx = tsubst_aggr_type (ctx, args,
-				  complain | tf_qualifying_scope,
-				  in_decl, /*entering_scope=*/1);
+	  ctx = tsubst_entering_scope (ctx, args,
+				       complain | tf_qualifying_scope,
+				       in_decl);
 	if (ctx == error_mark_node)
 	  return error_mark_node;
 
@@ -16914,8 +16867,10 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 
     case UNBOUND_CLASS_TEMPLATE:
       {
-	tree ctx = tsubst_aggr_type (TYPE_CONTEXT (t), args, complain,
-				     in_decl, /*entering_scope=*/1);
+	++processing_template_decl;
+	tree ctx = tsubst_entering_scope (TYPE_CONTEXT (t), args,
+					  complain, in_decl);
+	--processing_template_decl;
 	tree name = TYPE_IDENTIFIER (t);
 	tree parm_list = DECL_TEMPLATE_PARMS (TYPE_NAME (t));
 
@@ -21564,9 +21519,7 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 
 	   When we instantiate f<7>::S::g(), say, lookup_name is not
 	   clever enough to find f<7>::a.  */
-	enum_type
-	  = tsubst_aggr_type (DECL_CONTEXT (t), args, complain, in_decl,
-			      /*entering_scope=*/0);
+	enum_type = tsubst (DECL_CONTEXT (t), args, complain, in_decl);
 
 	for (v = TYPE_VALUES (enum_type);
 	     v != NULL_TREE;
@@ -21586,8 +21539,8 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	{
 	  tree ctx;
 
-	  ctx = tsubst_aggr_type (DECL_CONTEXT (t), args, complain, in_decl,
-				  /*entering_scope=*/1);
+	  ctx = tsubst_entering_scope (DECL_CONTEXT (t), args,
+				       complain, in_decl);
 	  if (ctx != DECL_CONTEXT (t))
 	    {
 	      tree r = lookup_field (ctx, DECL_NAME (t), 0, false);
@@ -21630,8 +21583,8 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	     TEMPLATE_DECL with `D<T>' as its DECL_CONTEXT.  Now we
 	     have to substitute this with one having context `D<int>'.  */
 
-	  tree context = tsubst_aggr_type (DECL_CONTEXT (t), args, complain,
-					   in_decl, /*entering_scope=*/true);
+	  tree context = tsubst_entering_scope (DECL_CONTEXT (t), args,
+						complain, in_decl);
 	  RETURN (lookup_field (context, DECL_NAME(t), 0, false));
 	}
       else
@@ -22161,8 +22114,8 @@ instantiate_template (tree tmpl, tree orig_args, tsubst_flags_t complain)
 	   already non-dependent, then we might as well use it.  */
 	ctx = DECL_CONTEXT (tmpl);
       else
-	ctx = tsubst_aggr_type (DECL_CONTEXT (gen_tmpl), targ_ptr,
-				complain, gen_tmpl, true);
+	ctx = tsubst_entering_scope (DECL_CONTEXT (gen_tmpl), targ_ptr,
+				     complain, gen_tmpl);
       push_nested_class (ctx);
     }
 
@@ -29324,8 +29277,8 @@ resolve_typename_type (tree type, bool only_current_p)
       tree args = TREE_OPERAND (fullname, 1);
       /* Instantiate the template.  */
       result = lookup_template_class (tmpl, args, NULL_TREE, NULL_TREE,
-				      /*entering_scope=*/true,
 				      tf_error | tf_user);
+      result = adjust_type_for_entering_scope (result);
       if (result == error_mark_node)
 	result = NULL_TREE;
     }
@@ -29564,7 +29517,7 @@ listify (tree arg)
   TREE_VEC_ELT (argvec, 0) = arg;
 
   return lookup_template_class (std_init_list, argvec, NULL_TREE,
-				NULL_TREE, 0, tf_warning_or_error);
+				NULL_TREE, tf_warning_or_error);
 }
 
 /* Replace auto in TYPE with std::initializer_list<auto>.  */
@@ -30510,7 +30463,7 @@ alias_ctad_tweaks (tree tmpl, tree uguides)
 	    fprime = copy_decl (fprime);
 	  tree fntype = TREE_TYPE (fprime);
 	  ret = lookup_template_class (TPARMS_PRIMARY_TEMPLATE (atparms), targs,
-				       in_decl, NULL_TREE, false, complain);
+				       in_decl, NULL_TREE, complain);
 	  fntype = build_function_type (ret, TYPE_ARG_TYPES (fntype));
 	  TREE_TYPE (fprime) = fntype;
 	  if (TREE_CODE (fprime) == TEMPLATE_DECL)
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 2dde65a970b..d0fa324fe5c 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -4011,8 +4011,10 @@ finish_template_type (tree name, tree args, int entering_scope)
   tree type;
 
   type = lookup_template_class (name, args,
-				NULL_TREE, NULL_TREE, entering_scope,
+				NULL_TREE, NULL_TREE,
 				tf_warning_or_error | tf_user);
+  if (entering_scope)
+    type = adjust_type_for_entering_scope (type);
 
   /* If we might be entering the scope of a partial specialization,
      find the one with the right constraints.  */