Here, instantiating B<short> requires instantiating A<short>, which
requires instantiating B<short>. Previously, that resulted in
creating two separate TYPE_DECLS for B<short> and trying to combine
them in register_specialization. Better, I think, to check for this
situation sooner.
Tested x86_64-pc-linux-gnu, applying to trunk.
commit f82ab957170984838b0bf4d9f7ef5d254eec28c3
Author: Jason Merrill <ja...@redhat.com>
Date: Mon Jun 18 11:53:39 2018 -0400
PR c++/86171 - ICE with recursive alias instantiation.
* pt.c (tsubst_decl): Handle recursive alias instantiation.
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 4ee84b201e9..6e590d4d342 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -13639,7 +13639,6 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
}
/* Create a new node for the specialization we need. */
- r = copy_decl (t);
if (type == NULL_TREE)
{
if (is_typedef_decl (t))
@@ -13664,7 +13663,16 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
sub_args = strip_innermost_template_args (args, extra);
}
type = tsubst (type, sub_args, complain, in_decl);
+ /* Substituting the type might have recursively instantiated this
+ same alias (c++/86171). */
+ if (gen_tmpl && DECL_ALIAS_TEMPLATE_P (gen_tmpl)
+ && (spec = retrieve_specialization (gen_tmpl, argvec, hash)))
+ {
+ r = spec;
+ break;
+ }
}
+ r = copy_decl (t);
if (VAR_P (r))
{
DECL_INITIALIZED_P (r) = 0;
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-65.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-65.C
new file mode 100644
index 00000000000..e320f3eedd0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-65.C
@@ -0,0 +1,10 @@
+// PR c++/86171
+// { dg-do compile { target c++11 } }
+
+template <class> struct A;
+template <class T> using B = typename A<T>::X;
+template <class T> struct A {
+ typedef int X;
+ typedef B<T> U;
+};
+B<short> b;
