On Mon, Oct 15, 2012 at 3:26 PM, Steven Bosscher wrote:
> On Mon, Oct 15, 2012 at 3:21 PM, Paolo Bonzini wrote:
>> Il 15/10/2012 14:53, Steven Bosscher ha scritto:
>>> I think I've shown above that we're all looking at the wrong pass...
>>
>> I think you have... so we want a patch like this?
>
> I don't think so. df_kill_notes is already supposed to take care of this.
But it doesn't because if the SET_DEST of an insn is the same as the
register dieing in the insn's REG_EQUAL note, the reg is live at the
end of the insn and so the note stays:
Breakpoint 2, df_kill_notes (insn=0x7ffff5e3e7e0, live=0x7fffffffda90)
at ../../trunk/gcc/df-problems.c:2833
2833 rtx *pprev = ®_NOTES (insn);
1: debug_rtx(insn) = (insn 79 50 52 8 (set (reg:DI 72 [ ivtmp.17D.1758 ])
(reg:DI 103 [ ivtmp.17D.1758 ])) -1
(expr_list:REG_DEAD (reg:DI 103 [ ivtmp.17D.1758 ])
(expr_list:REG_EQUAL (plus:DI (reg:DI 72 [ ivtmp.17D.1758 ])
(const_int 24 [0x18]))
(nil))))
void
(gdb) undisp 1
(gdb) p debug_bitmap(live)
first = 0x1627200 current = 0x1627200 indx = 0
0x1627200 next = (nil) prev = (nil) indx = 0
bits = { 6 7 16 20 72 82 85 87 }
$2 = void
(gdb)
So GCC should be looking at whether the reg in the REG_EQUAL note is
dead *before* the insn.
Bottom line: This is a bug in df_kill_notes.
Ciao!
Steven
