[gcc r11-6157] c++: Fix template parm ICE [PR 98297]

[gcc r11-6157] c++: Fix template parm ICE [PR 98297]

[Nathan Sidwell]

https://gcc.gnu.org/g:8d8bb85b48693a8a8a26e03ea4469888a1170f01

commit r11-6157-g8d8bb85b48693a8a8a26e03ea4469888a1170f01
Author: Nathan Sidwell <nathan@acm.org>
Date:   Wed Dec 16 11:49:41 2020 -0800

    c++: Fix template parm ICE [PR 98297]
    
    I think this is nonsense code, we seem to be naming an instantiation
    of a template template parm.  But this fixes the ICE.  Perhaps we
    should diagnose the issue earlier?
    
            gcc/cp/
            * parser.c (cp_parser_elaborated_type_specifier): Test
            BOUND_TEMPLATE_TEMPLATE_PARM before checking for instantiation.
            gcc/testsuite/
            * g++.dg/template/pr98297.C: New.

Diff:
---
 gcc/cp/parser.c                         | 4 +++-
 gcc/testsuite/g++.dg/template/pr98297.C | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 7ea8c28830e..3883339aa64 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -19650,7 +19650,9 @@ cp_parser_elaborated_type_specifier (cp_parser* parser,
       if (TREE_CODE (type) == TYPENAME_TYPE)
 	warning (OPT_Wattributes,
 		 "attributes ignored on uninstantiated type");
-      else if (tag_type != enum_type && CLASSTYPE_TEMPLATE_INSTANTIATION (type)
+      else if (tag_type != enum_type
+	       && TREE_CODE (type) != BOUND_TEMPLATE_TEMPLATE_PARM
+	       && CLASSTYPE_TEMPLATE_INSTANTIATION (type)
 	       && ! processing_explicit_instantiation)
 	warning (OPT_Wattributes,
 		 "attributes ignored on template instantiation");
diff --git a/gcc/testsuite/g++.dg/template/pr98297.C b/gcc/testsuite/g++.dg/template/pr98297.C
new file mode 100644
index 00000000000..0dd63a57b5c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/pr98297.C
@@ -0,0 +1,6 @@
+// PR 98297, ICE
+// { dg-do compile { target c++11 } }
+template <template <class> class a>
+struct [[b]]
+a <int>; // { dg-error "does not declare anything" }
+// { dg-warning "ignored" "" { target *-*-* } .-1 }