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Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."

From: Richard Kenner
Subject: Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
Date: Tue, 02 Jan 2007 08:36:53 EST

> | >|>   for (i = 1; i < m; ++i)
> | >|>     {
> | >|>       if (i > 0)
> | >|>         bar ();
> | >|>     }
> I suspect part of Richard K.'s questions has been to determine, based
> on data, what improvements we actually gain from doing that kind of
> elimination predicated on undefined-ness of signed integer
> arithmetic overflow.  It would be also useful to see how that affects
> inlining (for inlining, we may be able to adequately annotate the trees).
> I fear I haven't seen any.

Or even NOT based on data: even a list of those optimizations that VRP does
when it can assume no overflow that it couldn't do otherwise.  It would of
course be nicer to get real data, but even the list would be useful.

However, I have changed my mind on the particular case above, mostly due to
the argument about macros and that, in this case, the loop processing will
already assume that "i" doesn't overflow. Since it will make that assumption,
there's no reason for VRP not to as well.

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