This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Weird warning when building gcc


On Sat, Sep 23, 2017 at 12:34 PM, nick <xerofoify@gmail.com> wrote:
>
>
> On 2017-09-23 12:05 PM, Jeff Law wrote:
>> On 09/22/2017 08:25 PM, nick wrote:
>>> Greetings All,
>>>
>>> I am wondering if this is a warning worth looking into or is it just another false postive:
>>>
>>> /home/nick/gcc/gcc/combine.c:1316:8: warning: ‘prev’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>>>          if ((next = try_combine (insn, prev, NULL, NULL,
>>>
>>> Maybe it's just me being new to the project but is the code for that literally or also identical between this and the
>>> one where CC0 register is directly used.
>> Looks like a false positive to me.   Without more details (host, target,
>> flags, cpp output) I can't be 100% sure why it triggers though.
>>
>> Flow sensitive warnings such as this are very sensitive to a variety of
>> low level target and IL details.
>>
>>
>>
>> Jeff
>>
>
> Jeff,
>
> Thanks specifically what low level details do you need. It's currently on a x86-64 bit ubuntu host.
> Was build with the stock gcc from the ubuntu 17.04 repos with W=2 for extra warnings. What do these
> lines do, anything outside of the normal setting marcos as they seem to me:
>
>                 && GET_CODE (PATTERN (insn)) == SET
>                 && reg_mentioned_p (cc0_rtx, SET_SRC (PATTERN (insn)))
>
> I am wondering what GET_CODE,SET_SRC, PATTERN marcos do plus the function called, reg_mentioned_P?
> If your able to just tell me where the functions are located or how do you enable ctags for all of
> gcc? That would just save me asking stupid questions. Is there a global setting like make ctags for
> doing this or you I have to do it manually.
>
> Thanks for the quick response,
>
> Nick

I think I remember running into this warning before; it's because
stage 1 of bootstrap is built without optimization so the warnings
don't have as good information.

Right, here's the link to the end of the thread about it:
https://gcc.gnu.org/ml/gcc-patches/2016-09/msg00143.html


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]