On Sun, Dec 8, 2013 at 8:16 PM, Bin.Cheng <amker.cheng@xxxxxxxxx> wrote:
> On Sun, Dec 8, 2013 at 9:29 AM, Ian Lance Taylor <iant@xxxxxxxxxx> wrote:
>> On Sat, Dec 7, 2013 at 1:48 AM, Bin.Cheng <amker.cheng@xxxxxxxxx> wrote:
>>>
>>> I just found some GIMPLE like below is generated during boostrap gcc
>>> for x86, tree-vect-loop.c
>>>
>>>
>>> <bb 637>:
>>> # group_size_1432 = PHI <1(497), group_size_1017(660)>
>>> # scalar_dest_1287 = PHI <scalar_dest_1228(497), scalar_dest_1012(660)>
>>> ratio_1497 = group_size_1432 / 0;
>>> goto <bb 501>;
>>>
>>> The compilation ends fine, but what is the division by 0?
>>
>> Pretty hard to say without more information. I just tried, and I
>> don't see it myself. I would guess that some optimization split out
>> the ratio == 0 case for some reason.
>
> It disappeared with Richard's checkin r205730. Also I am not sure is
> why the rest of compiler can live with that code.
>
> The configuration option for me is :
> --disable-nls --disable-libmudflap --disable-libada --disable-libssp
> --disable-libquadmath --disable-libgomp --disable-libffi
> --disable-libstdcxx-pch --disable-tls --with-gnu-as --with-gnu-ld ...
> --enable-languages=c,c++
>
And the assembly finally generated is like:
.L4387:
movl 40(%esp), %eax # 6902 *movsi_internal/1 [length = 4]
xorl %ecx, %ecx # 7442 *movsi_xor [length = 2]
<----------------------
xorl %edx, %edx # 7443 *movsi_xor [length = 2]
divl %ecx # 7177 *udivmodsi4_noext [length = 2]
<----------------------
movl %eax, 68(%esp) # 6903 *movsi_internal/2 [length = 4]
jmp .L4474 # 8252 jump [length = 5]
Thanks,
bin
--
Best Regards.
