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

From: Robert Dewar
Subject: Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
Date: Tue, 02 Jan 2007 10:05:05 -0500
User-agent: Thunderbird (Windows/20061207)

Richard Guenther wrote:

We do that with -fstrict-aliasing, which also changes language semantics.
-fstrict-aliasing is disabled for -O0 and -O1 and enabled for -O[23s].

Yes, and as others have said, this is a bad precedent, and should
not be followed further. Inclusion of -fwrapv would be much worse,
since this has clearly and precisely defined semantics. In the
case of -fno-strict-aliasing, it is more like disabling an
optimization, since as far as I know there is no clear semantic
meaning for this flag (i.e. a meaning that could be expressed
formally at the level of the standard easily).

How do these switches implement your proposal?  "All optimiations" sounds
like the -fno-wrapv case we have now.

In a couple of ways:

First it can include semantics other than wrapping
Second, it allows completely unfettered optimization (see
password example), which I think no one would want to do
by default.


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