c++: abi_tag attribute on templates [PR109715]

We need to look through TEMPLATE_DECL when looking up the abi_tag
attribute (as with other function/variable declaration attributes).

	PR c++/109715

gcc/cp/ChangeLog:

	* mangle.cc (get_abi_tags): Strip TEMPLATE_DECL before looking
	up the abi_tag attribute.

gcc/testsuite/ChangeLog:

	* g++.dg/abi/abi-tag25.C: New test.
	* g++.dg/abi/abi-tag25a.C: New test.

gcc/cp/mangle.cc

@@ -530,6 +530,16 @@ get_abi_tags (tree t)
   if (DECL_P (t) && DECL_DECLARES_TYPE_P (t))
     t = TREE_TYPE (t);
 
+  if (TREE_CODE (t) == TEMPLATE_DECL && DECL_TEMPLATE_RESULT (t))
+    {
+      tree tags = get_abi_tags (DECL_TEMPLATE_RESULT (t));
+      /* We used to overlook abi_tag on function and variable templates.  */
+      if (tags && abi_check (19))
+	return tags;
+      else
+	return NULL_TREE;
+    }
+
   tree attrs;
   if (TYPE_P (t))
     attrs = TYPE_ATTRIBUTES (t);

gcc/testsuite/g++.dg/abi/abi-tag25.C

@@ -0,0 +1,17 @@
+// PR c++/109715
+// { dg-do compile { target c++11 } }
+
+template<class T>
+[[gnu::abi_tag("foo")]] void fun() { }
+
+template void fun<int>();
+
+#if __cpp_variable_templates
+template<class T>
+[[gnu::abi_tag("foo")]] int var = 0;
+
+template int var<int>;
+#endif
+
+// { dg-final { scan-assembler "_Z3funB3fooIiEvv" } }
+// { dg-final { scan-assembler "_Z3varB3fooIiE" { target c++14 } } }

gcc/testsuite/g++.dg/abi/abi-tag25a.C

@@ -0,0 +1,11 @@
+// PR c++/109715
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-fabi-version=18 -fabi-compat-version=18 -Wabi=0" }
+
+#include "abi-tag25.C"
+
+// { dg-warning "mangled name" "" { target *-*-* } 5 }
+// { dg-warning "mangled name" "" { target *-*-* } 11 }
+
+// { dg-final { scan-assembler "_Z3funIiEvv" } }
+// { dg-final { scan-assembler "_Z3varIiE" { target c++14 } } }