From: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
Subject: Re: Windows warnings from VS 2017
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
References: <f6488a36-4702-6d50-9fb4-fee10bb49497@2ndQuadrant.com>
 <8649.1505951694@sss.pgh.pa.us>
Message-ID: <acf6b500-0f91-cb38-d76b-17b6de29a606@2ndQuadrant.com>
Date: Wed, 20 Sep 2017 20:18:18 -0400
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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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