[PATCH] Fix PR c++/71182 - UB in parser.c

[Markus Trippelsdorf]

An -fsanitize=undefined instrumented compiler shows:

 cp/parser.c:768:7: runtime error: member call on null pointer of type 'struct 
vec'
  760 static inline cp_token *
  761 cp_lexer_previous_token (cp_lexer *lexer)
  762 {
  763   cp_token_position tp = cp_lexer_previous_token_position (lexer);
  764
  765   /* Skip past purged tokens.  */
  766   while (tp->purged_p)
  767     {
  768       gcc_assert (tp != lexer->buffer->address ());
  769       tp--;
  770     }
  771
  772   return cp_lexer_token_at (lexer, tp);
  773 }

(gdb) p *lexer
$1 = {
  buffer = 0x0,
  last_token = 0x7ffff7e0c2f8,
  next_token = 0x7ffff7e0c298,
  saved_tokens = {
    m_vec = 0x92c6b20
  },
  next = 0x7ffff5f96480,
  debugging_p = false,
  in_pragma = false
}

Fixed by guarding against the invalid member call on a null pointer.

Tested on ppc64le. Ok for trunk?

Thanks.

        PR c++/71182
        * parser.c (cp_lexer_previous_token): Guard against
        member call on null pointer.

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 08f5f9e52ef2..f430af97fdf1 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -765,7 +765,7 @@ cp_lexer_previous_token (cp_lexer *lexer)
   /* Skip past purged tokens.  */
   while (tp->purged_p)
     {
-      gcc_assert (tp != lexer->buffer->address ());
+      gcc_assert (!lexer->buffer || tp != lexer->buffer->address ());
       tp--;
     }
 
--
Markus