[Bug lto/65536] LTO line number information garbled

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

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

--- Comment #48 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
I run memory statistics with the cache and my patch. I will run stats with
cache w/o the libcpp patch tomorrow.  I would like to get this problem solved,
but perhaps we want to only track down the reason for wrong line numbers and do
more tuning next stage1 & backport.

I suppose I can implement checking that will lookup location after every insert
to double check lines are not garbled. Dropped columns are I guess acceptable
(it would be nice to drop the wrong carrets then)

So for memory use:
realloc_for_line_map is now at 16810000: 0.9% of GGC memory use pre-IPA. This
is definitly improvement. Gimple streaming however push it up to 75497496:4.2%
I guess this suggest that caching blocks and gimple stmt locators would make a
lot of difference.

ltrans report 4194328: 5.4% post main decl streaming, but before bodies are
read in.