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Re: [RFC] overflow checks optimized away

From: Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>
To: Greg Stark <stark(at)mit(dot)edu>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Bruce Momjian <bruce(at)momjian(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Xi Wang <xi(dot)wang(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [RFC] overflow checks optimized away
Date: 2013-11-29 20:36:00
Message-ID: 5298FAB0.5010203@vmware.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 11/29/2013 10:06 PM, Greg Stark wrote:
> On Fri, Nov 29, 2013 at 7:39 PM, Greg Stark <stark(at)mit(dot)edu> wrote:
>>
>> Just as an update I did get gcc to do the wrong thing on purpose. The
>> only overflow check that the regression tests find missing is the one
>> for int8abs() ie:
>
>
> Also, one of the places GCC warns about optimizing away an overflow
> check (with -fno-wrapv) is inside the localtime.c file from the tz
> library. I fixed it in my patch but in fact I checked and it's already
> fixed upstream so I'm wondering whether you expect to merge in an
> updated tz library? Is there anything surprising about the process or
> do you just copy in the files? Would you be happy for someone else to
> do it?

IIRC some files can be copied directly, but not all. Might be easiest to 
generate a diff between the last version in PostgreSQL and the latest 
upstream version, and apply that.

- Heikki


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