[gcc r12-7552] PR c++/96440: ICE-on-invalid-code error recovery.

[gcc r12-7552] PR c++/96440: ICE-on-invalid-code error recovery.

[Roger Sayle]

https://gcc.gnu.org/g:e52af9cac7fa7409c78c9f336dc1da57750c9766

commit r12-7552-ge52af9cac7fa7409c78c9f336dc1da57750c9766
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Tue Mar 8 23:33:46 2022 +0000

    PR c++/96440: ICE-on-invalid-code error recovery.
    
    This patch fixes PR c++/96440 which is an ICE-on-invalid-code regression
    affecting mainline.
    
    2022-03-08  Roger Sayle  <roger@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/cpp0x/pr96440.C: New test case.

Diff:
---
 gcc/cp/decl.cc                       | 6 ++++--
 gcc/testsuite/g++.dg/cpp0x/pr96440.C | 4 ++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 7f80f9d4d7a..de41b4de5ed 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/cpp0x/pr96440.C b/gcc/testsuite/g++.dg/cpp0x/pr96440.C
new file mode 100644
index 00000000000..000caf3197d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/pr96440.C
@@ -0,0 +1,4 @@
+/* { dg-do compile } */
+/* { dg-excess-errors "" } */
+
+auto alignas a [[]] [[const]] ();