https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83396
--- Comment #34 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Ok, reduced testcase for the -fcompare-debug (length) issue is just:
void fn1() {}
with -O2 -gdwarf-4 -fcompare-debug
The *.ira dump is still identical, but reload has:
--- pr83396.ii.276r.reload 2017-12-13 16:31:30.077467285 +0100
+++ pr83396.ii.gk.276r.reload 2017-12-13 16:31:30.144466454 +0100
@@ -6,10 +6,10 @@
Spilling non-eliminable hard regs: 1
New elimination table:
-Can eliminate 31 to 1 (offset=0, prev_offset=0)
-Can eliminate 111 to 1 (offset=0, prev_offset=0)
+Can eliminate 31 to 1 (offset=-32, prev_offset=0)
+Can eliminate 111 to 1 (offset=-32, prev_offset=0)
Can eliminate 111 to 31 (offset=0, prev_offset=0)
-Can eliminate 67 to 1 (offset=32, prev_offset=0)
+Can eliminate 67 to 1 (offset=0, prev_offset=0)
Can eliminate 67 to 31 (offset=32, prev_offset=0)
Can eliminate 30 to 30 (offset=0, prev_offset=0)
Spilling non-eliminable hard regs: 1
@@ -36,10 +36,10 @@ EBB 2
Spilling non-eliminable hard regs: 1
Spilling non-eliminable hard regs: 1
New elimination table:
-Can eliminate 31 to 1 (offset=0, prev_offset=0)
-Can eliminate 111 to 1 (offset=0, prev_offset=0)
+Can eliminate 31 to 1 (offset=-32, prev_offset=-32)
+Can eliminate 111 to 1 (offset=-32, prev_offset=-32)
Can eliminate 111 to 31 (offset=0, prev_offset=0)
-Can eliminate 67 to 1 (offset=32, prev_offset=32)
+Can eliminate 67 to 1 (offset=0, prev_offset=0)
Can eliminate 67 to 31 (offset=32, prev_offset=0)
Can eliminate 30 to 30 (offset=0, prev_offset=0)
differences.
The bug is obvious, rs6000_stack_info has:
else if (TARGET_XCOFF && write_symbols != NO_DEBUG)
info->push_p = 1;
so it generates different code based on whether -g is enabled or not.
Clearly that is a preexisting bug. If it is for whatever reason needed, can't
it be done regardless of -g, i.e.
else if (TARGET_XCOFF)
info->push_p = 1;
or, if you are ok with -fcompare-debug being broken for the default stabs or
whatever AIX uses for debugging (which implies different code generation
between -g and -g0), at least do it like:
else if (TARGET_XCOFF && write_symbols != NO_DEBUG && write_symbols !=
DWARF2_DEBUG)
info->push_p = 1;
