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

From: Vincent Lefevre
Subject: Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
Date: Sun, 31 Dec 2006 16:59:17 +0100
User-agent: Mutt/1.5.13-vl-r14963 (2006-12-20)

On 2006-12-31 10:08:32 -0500, Richard Kenner wrote:
> > Well, that's not equivalent. For instance, MPFR has many conditions
> > that evaluate to TRUE or FALSE on some/many implementations (mainly
> > because the type sizes depend on the implementation), even without
> > the assumption that an overflow cannot occur.
> Can you give an example of such a condition and show how an
> optimization that assumed overflows were undefined could break that
> code?

This won't break the code. But I'm saying that if the compiler assumes
wrapping, even in some particular cases (e.g. code that *looks like*
"overflow check"), it could miss some potential optimizations. That
is, it is not possible to avoid breaking overflow checks *and*
optimizing everything else.

Vincent Lefèvre <address@hidden> - Web: <>
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Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)

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