Re: [patch, rfc] Semantics of attribute (aligned), misscompilation of crtstuff

[Mark Mitchell <mark at codesourcery dot com>]

Zdenek Dvorak wrote:

>> I agree that the vectorizer has the right to increase alignment, but why
>> does the vectorizer want to vectorize this loop?
> 
> it does not; the vectorizer (more precisely, the increase_alignment pass
> that is run when vectorizer is enables) just unconditionally increases
> alignment of all arrays.

Oh, I see; it increases alignment in case it might be able to vectorize.

>> That doesn't seem like
>> much of a win, since there are no vectorizable accesses in the loop that
>> I can see.  If there's not a speed improvement, then this is just a
>> speed/space pessimization -- compounded by the code that you're adding
>> to check for NULLs.
> 
> I don't think the speed is important in this case.  Space might be,
> though.

Both matter, but space is a bigger concern; we use GCC on systems with
just a couple of kilobytes, and we need to be reducing overhead for
these sorts of things, not increasing it.

So, I think we should just turn the vectorizer off when compiling this file.

Thanks,

-- 
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713