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

[jakub at gcc dot gnu.org]

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

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dmalcolm at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
*.optimized looks the same, code generation diverges in *.expand.
The difference is that unique_locus_on_edge_between_p returns false vs. true
in between bb 2 and bb 4.
goto_locus is 0x80000002 in both cases, that expand_location to:
"pr104237.c":6:10 in both cases.
But the:
(insn 10005 10004 10007 2 (set (reg:QI 84 [ D.4728 ])
        (subreg:QI (reg:SI 86) 0)) "pr104237.c":6:10 -1
     (nil))
insn at the end of bb 2 has INSN_LOCATION 0x80000002 in the -g0 case and
INSN_LOCATION 0x80000004 in the -g case.
This means
799       if (insn != end && INSN_LOCATION (insn) == goto_locus)
800         return false;
in unique_locus_on_edge_between_p returns false in the -g0 case and true in -g
case and a nop is emitted only in the latter case.
The really strange thing is that (in the -g build):
(gdb) p expand_location (0x80000002)
$24 = {file = 0x3b6ba60 "pr104237.c", line = 6, column = 10, data =
0x7fffea06f180, sysp = false}
(gdb) p expand_location (0x80000004)
$25 = {file = 0x3b6ba60 "pr104237.c", line = 6, column = 10, data =
0x7fffea06f180, sysp = false}
i.e. everything is the same.
Even the adhoc table for 2 and 4:
(gdb) p line_table->location_adhoc_data_map.data[2]
$26 = {locus = 54368, src_range = {m_start = 54368, m_finish = 54368}, data =
0x7fffea06f180}
(gdb) p line_table->location_adhoc_data_map.data[4]
$27 = {locus = 58720, src_range = {m_start = 58720, m_finish = 58720}, data =
0x7fffea06f180}
contains different data, so even comparing LOCATION_LOCUS (INSN_LOCATION
(insn)) == LOCATION_LOCUS (goto_locus) wouldn't work here.

David, any idea on what the difference between 54368 and 58720 above could be
and why
(gdb) p expand_location (54368)
$28 = {file = 0x3b6ba60 "pr104237.c", line = 6, column = 10, data = 0x0, sysp =
false}
(gdb) p expand_location (58720)
$29 = {file = 0x3b6ba60 "pr104237.c", line = 6, column = 10, data = 0x0, sysp =
false}
?

Do we compare locations anywhere else (twice in cfgrtl.cc)?
Is the only reliable comparison expand_location and comparing the members of
that?