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Re: [Qemu-trivial] [PATCH v2] libvixl: a64: Skip "-Wunused-variable" for
From: |
Chen Gang |
Subject: |
Re: [Qemu-trivial] [PATCH v2] libvixl: a64: Skip "-Wunused-variable" for gcc 5.0.0 or higher |
Date: |
Wed, 15 Oct 2014 17:55:59 +0800 |
User-agent: |
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:31.0) Gecko/20100101 Thunderbird/31.1.2 |
On 10/15/14 4:47, Chen Gang wrote:
> On 10/15/2014 03:58 AM, Michael Tokarev wrote:
>>
>> That's what I'm after too (after trying to fix it properly).
>> And no, at this time I dont know how gcc5 handles this.
>>
>
> At present, I have sent the related information to gcc upstream mailing
> list for gcc5, we are just discussing about it.
>
> - Some gcc members stick to what gcc5 has done is correct (need still
> report warning).
>
> - But for me, I am just trying to get another gcc members' confirmation.
> I am not quite familiar with C++, for me it is a complex language, so
> I need additional confirmation by another gcc members, at least.
>
After consult the gcc related members, we are sure what gcc has done is
correct, and need process this warning in our qemu or 'libvixl'.
The related mail is below:
-------- Forwarded Message --------
Subject: Re: [Consult] g++: About "-Wunused-variable" for constant variable in
header file
Date: Wed, 15 Oct 2014 10:18:44 +0100
From: Jonathan Wakely <address@hidden>
To: Chen Gang <address@hidden>
CC: gcc-help <address@hidden>, Jeff Law <address@hidden>, Peter Maydell
<address@hidden>
On 14 October 2014 22:57, Chen Gang <address@hidden> wrote:
> Hello All:
>
> At present, I met one warning issue about gcc 5.0.0.
>
> - For "const float a = 3.4 - 2.1 / 3;", if it is unused, gcc5 will not
> report warning.
Because there is no cost to initializing the variable.
> - "const char n() {return 1;}; const a = n();", if 'a' is unused, gcc5
> will report warning.
Because it requires dynamic initialization, running a function at
startup, which has a cost. If you don't use the variable then you
might not want to run the initialization code at startup, so you get a
warning.
> For gcc old version (e.g. gcc4), it will not report warning. Is it the
> new feature for gcc5, or just a gcc5's bug?
I think this behaviour is intended and is not a bug.
--
Chen Gang
Open, share, and attitude like air, water, and life which God blessed