Re: Division by ZERO on GIMPLE?

["Bin.Cheng" <amker.cheng@gmail.com>]

On Mon, Dec 9, 2013 at 3:03 AM, Ian Lance Taylor <iant@google.com> wrote:
> On Sun, Dec 8, 2013 at 4:16 AM, Bin.Cheng <amker.cheng@gmail.com> wrote:
>> On Sun, Dec 8, 2013 at 9:29 AM, Ian Lance Taylor <iant@google.com> wrote:
>>> On Sat, Dec 7, 2013 at 1:48 AM, Bin.Cheng <amker.cheng@gmail.com> 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 compiler doesn't much care if you divide by zero.  Even if the
> programmer doesn't do such a thing, there are many ways that CSE can
> produce an integer division by zero.  Code that divides an integer by
> zero is valid C/C++ as long as it is never executed.  In fact, code
> that divides an integer by zero is valid Go even if it does get
> executed--Go defines what happens when an integer division by zero
> occurs (you get a runtime panic that can be caught).  So while I
> understand that the code looks odd, there is no reason the compiler
> shouldn't be able to handle it.
Hi Ian, thanks for your explanation.

Thanks,
bin

>
> Ian



-- 
Best Regards.