[Bug preprocessor/98882] [11 Regression] ICE in in cpp_directive_only_process on empty translation unit

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98882

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:ac16f4327fef5dfc288409371a61649253353ef7

commit r11-7093-gac16f4327fef5dfc288409371a61649253353ef7
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Feb 3 23:18:05 2021 +0100

    libcpp: Fix up -fdirectives-only preprocessing [PR98882]

    GCC 11 ICEs on all -fdirectives-only preprocessing when the files don't end
    with a newline.

    The problem is in the assertion, for empty TUs buffer->cur ==
buffer->rlimit
    and so buffer->rlimit[-1] access triggers UB in the preprocessor, for
    non-empty TUs it refers to the last character in the file, which can be
    anything.
    The preprocessor adds a '\n' character (or '\r', in particular if the
    user file ends with '\r' then it adds another '\r' rather than '\n'), but
    that is added after the limit, i.e. at buffer->rlimit[0].

    Now, if the routine handles occassional bumping of pos to buffer->rlimit +
1,
    I think it is just the assert that needs changing, usually we read from
*pos
    if pos < limit and then e.g. if it is '\r', look at the following character
    (which could be one of those '\n' or '\r' at buffer->rlimit[0]).  There is
    also the case where for '\\' before the limit we read following character
    and if it is '\n', do one thing, if it is '\r' read another character.
    But in that case if '\\' was the last char in the TU, the limit char will
be
    '\n', so we are ok.

    2021-02-03  Jakub Jelinek  <jakub@redhat.com>

            PR preprocessor/98882
            * lex.c (cpp_directive_only_process): Don't assert that rlimit[-1]
            is a newline, instead assert that rlimit[0] is either newline or
            carriage return.  When seeing '\\' followed by '\r', check limit
            before accessing pos[1].

            * gcc.dg/cpp/pr98882.c: New test.