Re: [HACKERS] Windows warnings from VS 2017 - Mailing list pgsql-hackers

From Andrew Dunstan
Subject Re: [HACKERS] Windows warnings from VS 2017
Date
Msg-id acf6b500-0f91-cb38-d76b-17b6de29a606@2ndQuadrant.com
Whole thread Raw
In response to Re: [HACKERS] Windows warnings from VS 2017  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: [HACKERS] Windows warnings from VS 2017
List pgsql-hackers

On 09/20/2017 07:54 PM, Tom Lane wrote:
> Andrew Dunstan <andrew.dunstan@2ndquadrant.com> writes:
>> It's also warning that it will copy 16 bytes to a 13 byte structure at
>> lines 518, 1293 and 1294 of src/backend/commands/dbcommands.c. I haven't
>> seen any ill effects of this so far, but it seems to indicate that
>> something is possibly amiss on this compiler with the MemSet macros.
> That's weird.  Is it too stupid to figure out that the if() inside
> MemSet evaluates to constant false in these calls?  It seems hard to
> see how it would realize that the loop will write 16 bytes if it doesn't
> propagate the constant value forward.
>
> However ... on some other compilers, I've noticed that the compiler seems
> more likely to make "obvious" deductions of that sort if the variables in
> question are marked const.  Does it help if you do
>
> -        void   *_vstart = (void *) (start); \
> -        int        _val = (val); \
> -        Size    _len = (len); \
> +        void   * const _vstart = (void *) (start); \
> +        const int    _val = (val); \
> +        const Size    _len = (len); \
>
>
> I don't think there's any strong reason not to just do s/MemSet/memset/
> in these calls and nearby ones, but it would be good to understand just
> what's wrong here.  And why it's only showing up in that file; seems
> nearly certain that we have similar coding elsewhere.
>
>             


I'll test it.

cheers

andrew

-- 
Andrew Dunstan                https://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services



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