cfgrtl: Fix up locus comparison in unique_locus_on_edge_between_p [PR104237]

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.