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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Michael Paquier <michael.paquier@gmail.com>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: Vincent Lachenal <vincent.lachenal@gmail.com>
Cc: PostgreSQL mailing lists <pgsql-bugs@postgresql.org>
Subject: Re: [BUGS] BUG #14897: Segfault on statitics SQL request
Date: Tue, 14 Nov 2017 00:31:35 -0500
Message-ID: <23171.1510637495@sss.pgh.pa.us> (raw)
In-Reply-To: <CAB7nPqQ7+rnOsGNDrtVC9uxb6erog2s4faM0FvmY_s-7uUmaNw@mail.gmail.com>
References: <20171110185747.31519.28038@wrigleys.postgresql.org>
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Michael Paquier <michael.paquier@gmail.com> writes:
> On Tue, Nov 14, 2017 at 12:31 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Concretely, the attached patch fixes it for me.  I've verified by
>> examining the assembly code that this stops gcc from using movdqa or
>> movaps in numeric.c, except for one place where it apparently can
>> prove that it's dealing with a sufficiently-aligned local variable.

> I am not seeing any difference in the assembly code generated by gcc
> -S with and without your patch. Perhaps I am missing something? What
> are you actually seeing?

Hm, double-check your procedure.  I get this:

$ diff numeric.s.std numeric.s.patch
2746c2746
<       movaps  %xmm0, (%r14)
---
>       movups  %xmm0, (%r14)
13948,13951c13948,13951
<       movdqa  16(%rbp), %xmm0
<       movaps  %xmm0, 16(%rax)
<       movdqa  32(%rbp), %xmm0
<       movaps  %xmm0, 32(%rax)
---
>       movdqu  16(%rbp), %xmm0
>       movups  %xmm0, 16(%rax)
>       movdqu  32(%rbp), %xmm0
>       movups  %xmm0, 32(%rax)
14434,14435c14434,14435
<       movdqa  16(%rbp), %xmm0
<       movaps  %xmm0, 16(%rax)
---
>       movdqu  16(%rbp), %xmm0
>       movups  %xmm0, 16(%rax)

(If using -g, there are a bunch more diffs in the debug tables.)

			regards, tom lane




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