Re: Anyone for adding -fwrapv to our standard CFLAGS?
От | Neil Conway |
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Тема | Re: Anyone for adding -fwrapv to our standard CFLAGS? |
Дата | |
Msg-id | 1134435720.15554.28.camel@localhost.localdomain обсуждение исходный текст |
Ответ на | Anyone for adding -fwrapv to our standard CFLAGS? (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: Anyone for adding -fwrapv to our standard CFLAGS?
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Список | pgsql-hackers |
On Mon, 2005-12-12 at 16:19 -0500, Tom Lane wrote: > It seems that gcc is up to some creative reinterpretation of basic C > semantics again; specifically, you can no longer trust that traditional > C semantics of integer overflow hold: > https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=175462 > > While I don't think we are anywhere using exactly the same trick that > the referenced mysql code is using, it certainly seems likely to me that > a compiler that is willing to replace "x < 0 && -x < 0" with "false" > might be able to break some of the integer overflow checks we do use. IMHO code that makes assumptions about overflow behavior beyond what is defined by the standard is asking for trouble, whether those assumptions are "traditional C semantics" or not. Given that -fwrapv apparently hurts performance *and* you've presented no evidence that we actually need the flag in the first place, I'm not sold on this idea... -Neil
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