Re: Current int & float overflow checking is slow.

On Mon, Oct 30, 2017 at 11:24 PM, Andres Freund <andres@anarazel.de> wrote:
>> >       Perhaps it should rather be pg_add_s32_overflow, or a similar
>> >       naming scheme?
>>
>> Not sure what the s is supposed to be?  Signed?
>
> Yes, signed. So we could add a u32 or something complementing the
> functions already in the patch. Even though overflow checks are a heck
> of a lot easier to write for unsigned ints, the intrinsics are still
> faster.  I don't have any sort of strong feelings on the naming.

Right, I guess including the s is probably a good idea then.

>> 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.
>
> I agree that we should do so at some point not too far away in the
> future. Not the least because we don't specify this kind of C dialect in
> a lot of other compilers. Additionally the flag causes some slowdown
> (because e.g. for loop variables are optimized less). But I'm fairly
> certain it needs a bit more care that I've invested as of now - should
> probably at least compile with -Wstrict-overflow=some-higher-level, and
> with ubsan. I'm fairly certain there's more bogus overflow checks
> around...

Makes sense.

-- 
Robert Haas
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