Re: compiler warnings with gcc 4.8 and -Og

Hi,

On 2022-06-02 13:24:28 +0900, Michael Paquier wrote:
> On Wed, Jun 01, 2022 at 09:42:44PM -0500, Justin Pryzby wrote:
> > Today's "warnings" thread suggests to me that these are worth fixing - it seems
> > reasonable to compile postgres 14 on centos7 (as I sometimes have done), and
> > the patch seems even more reasonable when backpatched to older versions.
> > (Also, I wonder if there's any consideration to backpatch cirrus.yaml, which
> > uses -Og)
>
> https://en.wikipedia.org/wiki/CentOS#CentOS_releases tells that centos
> 7 will be supported until the end of 2024, so I would fix that.

To me fixing gcc 4.8 warnings feels like a fools errand, unless they're
verbose enough to make compilation exceedingly verbose (e.g. warnings in a
header).

> > The patch below applies and fixes warnings back to v13.
>
> I don't mind fixing what you have here, as a first step. All those
> cases are telling us that the compiler does not see PG_TRY() as
> something is can rely on to set up each variable. 7292fd8 is
> complaining about the same point, actually, aka setjmp clobberring the
> variable, isn't it? So wouldn't it be better to initialize them, as
> your patch does, but also mark them as volatile? In short, what
> happens with -Wclobber and a non-optimized compilation?

FWIW, I found -Wclobber to be so buggy as to be pointless.

I don't think it needs be volatile because it'll not be accessed if we error
out? At least in the first instances in Justin's patch.

Greetings,

Andres Freund