[C++ PATCH] PR c++/96440: ICE-on-invalid-code error recovery.

[Roger Sayle]

This patch fixes PR c++/96440 which is an ICE-on-invalid-code regression
affecting mainline.

This patch has been tested on x86_64-pc-linux-gnu, enabling languages
c and c++, with make bootstrap and make -k check with no new failures.
Ok for mainline?

2022-03-07  Roger Sayle  <ro...@nextmovesoftware.com>

gcc/cp/ChangeLog
        PR c++/96440
        * decl.cc (start_decl): Defend against prefix_attributes being
        error_mark_node.

gcc/testsuite/ChangeLog
        PR c++/96440
        * g++.dg/pr96440.C: New test case.

Roger
--


diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 7f80f9d..de41b4d 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -5483,13 +5483,15 @@ start_decl (const cp_declarator *declarator,
 
   *pushed_scope_p = NULL_TREE;
 
-  attributes = chainon (attributes, prefix_attributes);
+  if (prefix_attributes != error_mark_node)
+    attributes = chainon (attributes, prefix_attributes);
 
   decl = grokdeclarator (declarator, declspecs, NORMAL, initialized,
                         &attributes);
 
   if (decl == NULL_TREE || VOID_TYPE_P (decl)
-      || decl == error_mark_node)
+      || decl == error_mark_node
+      || prefix_attributes == error_mark_node)
     return error_mark_node;
 
   context = CP_DECL_CONTEXT (decl);
diff --git a/gcc/testsuite/g++.dg/pr96440.C b/gcc/testsuite/g++.dg/pr96440.C
new file mode 100644
index 0000000..212271f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr96440.C
@@ -0,0 +1,5 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-excess-errors "" } */
+
+auto alignas a [[]] [[const]] ();