c: Fix sizeof error recovery [PR117745]

Compilation of the following testcase hangs forever after emitting first
error.  The problem is that in one place we just return error_mark_node
directly rather than going through c_expr_sizeof_expr or c_expr_sizeof_type.
The parsing of the expression could have called record_maybe_used_decl
though, but nothing calls pop_maybe_used which needs to be called after
parsing of every sizeof/typeof, successful or not.
At the end of the toplevel declaration we free the parser_obstack and in
another function record_maybe_used_decl is called again and due to the
missing pop_maybe_unused we end up with a cycle in the chain.

The following patch fixes it by just setting error and goto to the
    sizeof_expr:
      c_inhibit_evaluation_warnings--;
      in_sizeof--;
      mark_exp_read (expr.value);
      if (TREE_CODE (expr.value) == COMPONENT_REF
          && DECL_C_BIT_FIELD (TREE_OPERAND (expr.value, 1)))
        error_at (expr_loc, "%<sizeof%> applied to a bit-field");
      result = c_expr_sizeof_expr (expr_loc, expr);
where c_expr_sizeof_expr will do:
  struct c_expr ret;
  if (expr.value == error_mark_node)
    {
      ret.value = error_mark_node;
      ret.original_code = ERROR_MARK;
      ret.original_type = NULL;
      ret.m_decimal = 0;
      pop_maybe_used (false);
    }
...
  return ret;
which is exactly what the old code did manually except for the missing
pop_maybe_used call.  mark_exp_read does nothing on error_mark_node and
error_mark_node doesn't have COMPONENT_REF tree_code.

2024-11-27  Jakub Jelinek  <jakub@redhat.com>

	PR c/117745
	* c-parser.cc (c_parser_sizeof_expression): If type_name is NULL,
	just expr.set_error () and goto sizeof_expr instead of doing error
	recovery manually.

	* gcc.dg/pr117745.c: New test.

1 files changed, 5 insertions, 7 deletions

diff --git a/gcc/c/c-parser.cc b/gcc/c/c-parser.cc
index 730f70b..0e6f87e 100644
--- a/gcc/c/c-parser.cc
+++ b/gcc/c/c-parser.cc
@@ -10416,13 +10416,11 @@ c_parser_sizeof_expression (c_parser *parser)
       finish = parser->tokens_buf[0].location;
       if (type_name == NULL)
 	{
-	  struct c_expr ret;
-	  c_inhibit_evaluation_warnings--;
-	  in_sizeof--;
-	  ret.set_error ();
-	  ret.original_code = ERROR_MARK;
-	  ret.original_type = NULL;
-	  return ret;
+	  /* Let c_expr_sizeof_expr call pop_maybe_used and fill in c_expr
+	     for parsing error; the parsing of the expression could have
+	     called record_maybe_used_decl.  */
+	  expr.set_error ();
+	  goto sizeof_expr;
 	}
       if (c_parser_next_token_is (parser, CPP_OPEN_BRACE))
 	{