From b1e701dc4adb11a5ed5f45c2fb31ba4689b718d0 Mon Sep 17 00:00:00 2001
From: Nathan Sidwell <nathan@acm.org>
Date: Tue, 4 Jan 2022 13:36:44 -0800
Subject: [PATCH] [c++] Adjust mark used member in instantiated class scope

The fix for PR97966 caused a regression with (non-template) member
functions of template classes.  We need to mark them used in the
instantiated class's scope, rather than the scope we were in before
instantiating, as the latter may itself be in template and change the
behaviour of marking a function as used.

	gcc/cp/
	* pt.c (instantiate_class_template_1): Process attribute((used)) set
	in class's context.
	gcc/testsuite/
	* g++.dg/template/attr-used.C: New.
---
 gcc/cp/pt.c                               | 13 ++++++++-----
 gcc/testsuite/g++.dg/template/attr-used.C | 16 ++++++++++++++++
 2 files changed, 24 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/template/attr-used.C

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index c587966..0fa4a16 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -12277,6 +12277,14 @@ instantiate_class_template_1 (tree type)
 
   perform_instantiation_time_access_checks (pattern, args);
   perform_deferred_access_checks (tf_warning_or_error);
+
+  /* Now that we've gone through all the members, instantiate those
+     marked with attribute used.  We must do this in the context of
+     the class -- not the context we pushed from, as that might be
+     inside a template and change the behaviour of mark_used.  */
+  for (tree x : used)
+    mark_used (x);
+
   pop_nested_class ();
   maximum_field_alignment = saved_maximum_field_alignment;
   if (!fn_context)
@@ -12290,11 +12298,6 @@ instantiate_class_template_1 (tree type)
   if (TYPE_CONTAINS_VPTR_P (type) && CLASSTYPE_KEY_METHOD (type))
     vec_safe_push (keyed_classes, type);
 
-  /* Now that we've gone through all the members, instantiate those
-     marked with attribute used.  */
-  for (tree x : used)
-    mark_used (x);
-
   return type;
 }
 
diff --git a/gcc/testsuite/g++.dg/template/attr-used.C b/gcc/testsuite/g++.dg/template/attr-used.C
new file mode 100644
index 0000000..e12bf4c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/attr-used.C
@@ -0,0 +1,16 @@
+// { dg-do compile }
+
+template<typename T> struct X {
+  void g () {}
+  void f () __attribute__((__used__)) {}
+};
+
+extern X<int> x; // X<int> incomplete here
+
+template <typename T>
+void Frob (T t) {
+  x.g(); // X<int> completed here, X<int>::f's body marked for instantiation
+}
+
+// Make sure X<int>::f is emitted
+// { dg-final { scan-assembler "_ZN1XIiE1fEv:" } }
-- 
2.7.4