[Bug middle-end/56231] warning traces have bogus line information when using LTO

["rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56231

--- Comment #6 from rguenther at suse dot de <rguenther at suse dot de> 2013-02-08 09:07:09 UTC ---
On Thu, 7 Feb 2013, manu at gcc dot gnu.org wrote:

> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56231
> 
> Manuel L?pez-Ib??ez <manu at gcc dot gnu.org> changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>                  CC|                            |manu at gcc dot gnu.org
> 
> --- Comment #5 from Manuel L?pez-Ib??ez <manu at gcc dot gnu.org> 2013-02-07 19:10:17 UTC ---
> /* Reason for creating a new line map with linemap_add.  LC_ENTER is
>    when including a new file, e.g. a #include directive in C.
>    LC_LEAVE is when reaching a file's end.  LC_RENAME is when a file
>    name or line number changes for neither of the above reasons
>    (e.g. a #line directive in C); LC_RENAME_VERBATIM is like LC_RENAME
>    but a filename of "" is not specially interpreted as standard
>    input. LC_ENTER_MACRO is when a macro expansion is about to start.  */
> 
> So perhaps the secret is to use just LC_ENTER?

Hmm, I guessed that eventually the "included from" stuff is
built by nesting LC_ENTER w/o LC_LEAVE, so that probably makes it worse.

At least I see we do an initial

  linemap_add (line_table, LC_ENTER, 0, NULL, 0);

which might explain the single "included from" with bogus info.
But ISTR other frontends do sth similar.  Though now I'm curious
what breaks if we remove the above from lto/lto-lang.c