From f7f4628054358a92a55d52645cf107aa26ff6765 Mon Sep 17 00:00:00 2001
From: Patrick Palka <ppalka@redhat.com>
Date: Fri, 7 Oct 2022 12:01:58 -0400
Subject: [PATCH] c++ modules: ICE with bitfield in class template

According to grokbitfield, DECL_BIT_FIELD_REPRESENTATIVE contains the
width of the bitfield until we layout the class type (after which it'll
contain a decl).  Thus for a bitfield in a class template it'll always
be the width, and this patch makes us avoid ICEing from mark_class_def
in this case.

gcc/cp/ChangeLog:

	* module.cc (trees_out::mark_class_def): Guard against
	DECL_BIT_FIELD_REPRESENTATIVE not being a decl.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/bfield-3.H: New test.
---
 gcc/cp/module.cc                        | 6 +++++-
 gcc/testsuite/g++.dg/modules/bfield-3.H | 8 ++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/modules/bfield-3.H

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index cb1929bc5d5..94fbee85225 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -11919,7 +11919,11 @@ trees_out::mark_class_def (tree defn)
 	mark_class_member (member);
 	if (TREE_CODE (member) == FIELD_DECL)
 	  if (tree repr = DECL_BIT_FIELD_REPRESENTATIVE (member))
-	    mark_declaration (repr, false);
+	    /* If we're marking a class template definition, then
+	       this'll contain the width (as set by grokbitfield)
+	       instead of a decl.  */
+	    if (DECL_P (repr))
+	      mark_declaration (repr, false);
       }
 
   /* Mark the binfo hierarchy.  */
diff --git a/gcc/testsuite/g++.dg/modules/bfield-3.H b/gcc/testsuite/g++.dg/modules/bfield-3.H
new file mode 100644
index 00000000000..4fd4db7116a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/bfield-3.H
@@ -0,0 +1,8 @@
+// { dg-additional-options -fmodule-header }
+// { dg-module-cmi {} }
+
+template<int N>
+struct A {
+  int x : 1;
+  int y : N;
+};