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

[Robert Dewar <dewar at adacore dot com>]

Richard Kenner wrote:
> > Not so appalling really, given that relying on wrapping is as has
> > been pointed out in this thread, the most natural and convenient way
> > of testing for overflow. It is really *quite* difficult to test for
> > overflow while avoiding overflow, and this is something that is
> > probably not in the lexicon of many C programmers.
>
> I guess that's true even in GCC.  I looked at the OVERFLOW_SUM_SIGN macro in
> fold-const.c.  But on the positive side, the test is isolated in one place
> and so is easy to fix.

It would make sense as was suggested earlier to define standard library
routines or macros for overflow detection, and indeed this would be a
useful and appropriate addition to the standard

> Moreover, as was said earlier in this thread, although it's hard to formally
> define the subset, it's hard to see how any of the optimizations proposed
> that take advantage of undefined overflow would, in pratice, actually break
> this idiom.