[Bug lto/65536] LTO line number information garbled

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65536

--- Comment #23 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #15)
> (In reply to Jakub Jelinek from comment #14)
> > By streaming the line_table directly you'd stream lots of location_t that
> > are not actually used for anything that is streamed into the LTO.
> > I don't understand why the tables would be huge, the string would of course
> > use normal LTO section string sharing, and if we stream right now every
> > location_t as the triplet, it would mean in case a single location_t is
> > never used by more than one tree we'd stream an integer extra to what we
> > stream now (just the triplets would be streamed in a different place), but
> > in the more common case where one location_t is used by many trees, we'd
> > stream less than what we stream now, due to the additional indirection.
> 
[...]
> Of course, if you are really unlucky, each location_t used by LTO may belong
> to a different map, thus you cannot remove anything and then it would have
> been more efficient to use a file:line:column table. In this worst case, the
> overhead would be approximately sizeof(struct line_map) * number of rows in
> the file:line:column table.

In fact, looking at 

struct GTY(()) line_map_ordinary {
  const char *to_file;
  linenum_type to_line;

  /* An index into the set that gives the line mapping at whose end
     the current one was included.  File(s) at the bottom of the
     include stack have this set to -1.  */
  int included_from;

  /* SYSP is one for a system header, two for a C system header file
     that therefore needs to be extern "C" protected in C++, and zero
     otherwise.  This field isn't really needed now that it's in
     cpp_buffer.  */
  unsigned char sysp;

  /* Number of the low-order source_location bits used for a column number.  */
  unsigned int column_bits : 8;
};

If we do not care about sysp and included_from, then even in the worst case, it
will be more efficient to stream out the line_table than the file:line:column
table.

And it has the benefit that it is already sorted and the location_t values
within trees/gimple can be streamed out directly without calling linemap_lookup
to get the file:line:column for each of them. And since a location_t takes 1/3
of space that file:line:column, that would reduce the streamed out data even
further.
>From gcc-bugs-return-481507-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Tue Mar 24 19:58:26 2015
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From: "paolo.carlini at oracle dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/61358] Bogus "duplicate label" error after label used within C++11 lambda
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ida358

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-03-24
                 CC|                            |paolo.carlini at oracle dot com
             Blocks|                            |54367
     Ever confirmed|0                           |1