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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: Sat, 30 Dec 2006 19:22:40 -0500
User-agent: Thunderbird (Windows/20061207)

Richard Kenner wrote:
Note the interesting places in VRP where it assumes undefined signed
overflow is in compare_values -- we use the undefinedness to fold

Unfortunately, comparisons are the trickiest case because you have to
be careful to avoid deleting a comparison that exists to see if overflow
occured: this is perhaps the most common place where wrapping is assumed.

Note incidentally regarding Fortran that testing for overflow is
at least as difficult in Fortran as in C (unless new stuff has been
added to Fortran since my Fortran days, which is certainly possible).

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