[PATCH] c++: Handle erroneous DECL_LOCAL_DECL_ALIAS in duplicate_decls [PR107575]

[Simon Martin]

We currently ICE upon the following because we don't properly handle local
functions with an error_mark_node as DECL_LOCAL_DECL_ALIAS in duplicate_decls.

=== cut here ===
void f (void) {
  virtual int f (void) const;
  virtual int f (void);
}
=== cut here ===

This patch fixes this by checking for error_mark_node.

Successfully tested on x86_64-pc-linux-gnu.

        PR c++/107575

gcc/cp/ChangeLog:

        * decl.cc (duplicate_decls): Check for error_mark_node
        DECL_LOCAL_DECL_ALIAS.

gcc/testsuite/ChangeLog:

        * g++.dg/parse/crash74.C: New test.

---
 gcc/cp/decl.cc                       | 11 +++++++----
 gcc/testsuite/g++.dg/parse/crash74.C | 11 +++++++++++
 2 files changed, 18 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/parse/crash74.C

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index d481e1ec074..2ae46143d70 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -2792,10 +2792,13 @@ duplicate_decls (tree newdecl, tree olddecl, bool 
hiding, bool was_hidden)
          retrofit_lang_decl (newdecl);
          tree alias = DECL_LOCAL_DECL_ALIAS (newdecl)
            = DECL_LOCAL_DECL_ALIAS (olddecl);
-         DECL_ATTRIBUTES (alias)
-           = (*targetm.merge_decl_attributes) (alias, newdecl);
-         if (TREE_CODE (newdecl) == FUNCTION_DECL)
-           merge_attribute_bits (newdecl, alias);
+         if (alias != error_mark_node)
+           {
+             DECL_ATTRIBUTES (alias) =
+               (*targetm.merge_decl_attributes) (alias, newdecl);
+             if (TREE_CODE (newdecl) == FUNCTION_DECL)
+               merge_attribute_bits (newdecl, alias);
+           }
        }
     }
 
diff --git a/gcc/testsuite/g++.dg/parse/crash74.C 
b/gcc/testsuite/g++.dg/parse/crash74.C
new file mode 100644
index 00000000000..a7ba5094be6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/crash74.C
@@ -0,0 +1,11 @@
+// PR c++/107575
+
+void f (void) {
+  virtual int f (void) const; // { dg-line line_4 }
+  virtual int f (void); // { dg-line line_5 }
+}
+
+// { dg-error "outside class declaration" {} { target *-*-* } line_4 }
+// { dg-error "cannot have cv-qualifier" {} { target *-*-* } line_4 }
+// { dg-error "ambiguating new declaration of" {} { target *-*-* } line_4 }
+// { dg-error "outside class declaration" {} { target *-*-* } line_5 }
-- 
2.44.0