From: | Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Windows warnings from VS 2017 |
Date: | 2017-09-21 02:26:42 |
Message-ID: | c8fc2cd2-584f-1bf7-8d4a-ae05db709ad2@2ndQuadrant.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On 09/20/2017 08:18 PM, Andrew Dunstan wrote:
>
> On 09/20/2017 07:54 PM, Tom Lane wrote:
>> Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)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.
>
Doesn't make a difference. I agree it would be good to understand what's
going on.
cheers
andrew
--
Andrew Dunstan https://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
From | Date | Subject | |
---|---|---|---|
Next Message | Andres Freund | 2017-09-21 02:32:36 | Re: POC: Cache data in GetSnapshotData() |
Previous Message | Robert Haas | 2017-09-21 02:22:00 | Re: POC: Cache data in GetSnapshotData() |