[C++ PATCH] Avoid UB in cp_lexer_previous_token (PR c++/71182)

[Jakub Jelinek]

Hi!

cp_lexer_new_from_tokens creates lexer that has NULL lexer->buffer,
calling lexer->buffer->address () therefore is UB (diagnosed by
--with-boot-config=bootstrap-ubsan).

The following patch fixes this, or Markus offered
      gcc_assert (!lexer->buffer || tp != lexer->buffer->address ());
instead.  Bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk (or do you prefer Markus' version)?

2017-01-03  Jakub Jelinek  <ja...@redhat.com>

        PR c++/71182
        * parser.c (cp_lexer_previous_token): Use vec_safe_address in the
        assertion, as lexer->buffer may be NULL.

        * g++.dg/cpp0x/pr71182.C: New test.

--- gcc/cp/parser.c.jj  2017-01-03 09:58:13.000000000 +0100
+++ gcc/cp/parser.c     2017-01-03 11:39:56.940595981 +0100
@@ -766,7 +766,7 @@ cp_lexer_previous_token (cp_lexer *lexer
   /* Skip past purged tokens.  */
   while (tp->purged_p)
     {
-      gcc_assert (tp != lexer->buffer->address ());
+      gcc_assert (tp != vec_safe_address (lexer->buffer));
       tp--;
     }
 
--- gcc/testsuite/g++.dg/cpp0x/pr71182.C.jj     2017-01-03 11:44:19.400246340 
+0100
+++ gcc/testsuite/g++.dg/cpp0x/pr71182.C        2017-01-03 11:44:04.795432815 
+0100
@@ -0,0 +1,12 @@
+// PR c++/71182
+// { dg-do compile { target c++11 } }
+
+class A {
+  template <typename> void As();
+};
+template <typename T> class B : A {
+  void f() {
+    A *g ;
+    g ? g->As<T>() : nullptr;
+  }
+};

        Jakub