[Bug lto/104237] [11/12 Regression] Emitted binary code changes when -g is enabled at -O1 -flto and optimize attribute since r11-3126-ga8f9b4c54cc35062

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104237

--- Comment #7 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:430dca620fa3d03e53f6771a2b61d3f0ebb73756

commit r12-6914-g430dca620fa3d03e53f6771a2b61d3f0ebb73756
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Jan 28 11:48:18 2022 +0100

    cfgrtl: Fix up locus comparison in unique_locus_on_edge_between_p
[PR104237]

    The testcase in the PR (not included for the testsuite because we don't
    have an (easy) way to -fcompare-debug LTO, we'd need 2
compilations/linking,
    one with -g and one with -g0 and -fdump-rtl-final= at the end of lto1
    and compare that) has different code generation for -g vs. -g0.

    The difference appears during expansion, where we have a goto_locus
    that is at -O0 compared to the INSN_LOCATION of the previous and next insn
    across an edge.  With -g0 the locations are equal and so no nop is added.
    With -g the locations aren't equal and so a nop is added holding that
    location.

    The reason for the different location is in the way how we stream in
    locations by lto1.
    We have lto_location_cache::apply_location_cache that is called with some
    set of expanded locations, qsorts them, creates location_t's for those
    and remembers the last expanded location.
    lto_location_cache::input_location_and_block when read in expanded_location
    is equal to the last expanded location just reuses the last location_t
    (or adds/changes/removes LOCATION_BLOCK in it), when it is not queues
    it for next apply_location_cache.  Now, when streaming in -g input, we can
    see extra locations that don't appear with -g0, and if we are unlucky
    enough, those can be sorted last during apply_location_cache and affect
    what locations are used from the single entry cache next.
    In particular, second apply_location_cache with non-empty loc_cache in
    the testcase has 14 locations with -g0 and 16 with -g and those 2 extra
    ones sort both last (they are the same).  The last one from -g0 then
    appears to be input_location_and_block sourced again, for -g0 triggers
    the single entry cache, while for -g it doesn't and so apply_location_cache
    will create for it another location_t with the same content.

    The following patch fixes it by comparing everything we care about the
    location instead (well, better in addition) to a simple location_t ==
    location_t check.  I think we don't care about the sysp flag for debug
    info...

    2022-01-28  Jakub Jelinek  <jakub@redhat.com>

            PR lto/104237
            * cfgrtl.cc (loc_equal): New function.
            (unique_locus_on_edge_between_p): Use it.