Re: Current int & float overflow checking is slow.

From: ilmari(at)ilmari(dot)org (Dagfinn Ilmari =?utf-8?Q?Manns=C3=A5ker?=)
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Andres Freund <andres(at)anarazel(dot)de>, "pgsql-hackers\(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Greg Stark <stark(at)mit(dot)edu>
Subject: Re: Current int & float overflow checking is slow.
Date: 2017-10-30 18:12:58
Message-ID: d8ja8084i8l.fsf@dalvik.ping.uio.no
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Robert Haas <robertmhaas(at)gmail(dot)com> writes:

>> 0003) Removes -fwrapv. I'm *NOT* suggesting we apply this right now, but
>> it seems like an important test for the new facilities. Without
>> 0002, tests would fail after this, after it all tests run
>> successfully.
>
> I suggest that if we think we don't need -fwrapv any more, we ought to
> remove it. Otherwise, we won't find out if we're wrong.

Without -fwrapv signed overflow is undefined behaviour. We should test
thoroughly with -ftrapv or -fsanitize=signed-integer-overflow to be
confident the code is free of such things. We might even want to enable
-ftrapv by default in cassert-enabled builds.

- ilmari
--
"I use RMS as a guide in the same way that a boat captain would use
a lighthouse. It's good to know where it is, but you generally
don't want to find yourself in the same spot." - Tollef Fog Heen

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