From e53ec543e66382d2552e89077e05fe70e2a75c78 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Wed, 3 Apr 2019 17:51:36 -0400
Subject: [PATCH] PR c++/81866 - ICE with member template and default targ.

This testcase manages to find a way to look up the partial instantiation of
B for the default argument of C before we've created the partial
instantiation of B as part of the normal instantiation of the members of A.
Which we can deal with, but we were getting confused because the partial
instantiation was stored with a RECORD_TYPE specialization rather than
TEMPLATE_DECL.

	* pt.c (tsubst_template_decl): Handle getting a type from
	retrieve_specialization.

From-SVN: r270138
---
 gcc/cp/ChangeLog                         |  4 ++++
 gcc/cp/pt.c                              |  8 +++++++-
 gcc/testsuite/g++.dg/template/memtmpl6.C | 13 +++++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/template/memtmpl6.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 91d14311f18..888b431e099 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,9 @@
 2019-04-03  Jason Merrill  <jason@redhat.com>
 
+	PR c++/81866 - ICE with member template and default targ.
+	* pt.c (tsubst_template_decl): Handle getting a type from
+	retrieve_specialization.
+
 	PR c++/86586 - -fcompare-debug=-Wsign-compare.
 	* typeck.c (cp_build_binary_op): Don't fold for -Wsign-compare.
 
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 2b92b608f5d..9cb29d22ca3 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -13266,7 +13266,13 @@ tsubst_template_decl (tree t, tree args, tsubst_flags_t complain,
       hash = hash_tmpl_and_args (t, full_args);
       spec = retrieve_specialization (t, full_args, hash);
       if (spec != NULL_TREE)
-	return spec;
+	{
+	  if (TYPE_P (spec))
+	    /* Type partial instantiations are stored as the type by
+	       lookup_template_class_1, not here as the template.  */
+	    spec = CLASSTYPE_TI_TEMPLATE (spec);
+	  return spec;
+	}
     }
 
   /* Make a new template decl.  It will be similar to the
diff --git a/gcc/testsuite/g++.dg/template/memtmpl6.C b/gcc/testsuite/g++.dg/template/memtmpl6.C
new file mode 100644
index 00000000000..9ce35abfc4e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/memtmpl6.C
@@ -0,0 +1,13 @@
+// PR c++/81866
+
+template<class>
+struct A {
+  template<class> struct C;
+  template<class> struct B;
+  template<class T = B<int> > struct C {};
+};
+
+int main() {
+  A<int>::C<> ac;
+  return 0;
+}
-- 
2.30.2